JP7523786B2 - Optical thin film filters and beam shapers - Google Patents

Description

The present invention relates to an optical thin film filter and a beam shaper that can change the cross-sectional intensity distribution of a light beam.

A filter described in Patent Document 1 (JP-B-7-102470) is known as a beam shaper capable of changing the cross-sectional intensity distribution of a beam emitted from a laser.
As shown in FIG. 2, this filter changes the cross-sectional intensity distribution of the beam from a Gaussian distribution A (Gaussian type) to a flat intensity distribution C (flat-top type).
In laser processing, when the cross-sectional intensity distribution of the beam is changed from a Gaussian type, which is a general form immediately after oscillation, to a flat-top type, the cutting of the thick plate is performed more smoothly. That is, with the Gaussian type, the cross section (penetration shape) of the processed part of the thick plate during cutting becomes a mortar shape, making it difficult to ensure a predetermined depth or more of the processed part, and the cutting of the thick plate does not proceed halfway. In contrast, with the flat-top type, the penetration shape becomes a columnar shape, ensuring the depth of the processed part during cutting, and completing the cutting of the thick plate.
As described in [0023], this filter is constructed by imparting a film thickness gradient to a light-transmitting plate, by making a light-transmitting plate containing a transparent material with a density gradient that has an absorption spectrum in the same wavelength range, or by forming a thin metal film such as aluminum on the surface of a transparent plate by vacuum deposition or the like so that the film thickness varies (apodizing filter).

As a similar filter, a phase plate is known, as described in Patent Document 2 (JP-A-2002-98930).
As shown in [0022], FIG. 2 and FIG. 3, this phase plate has two concentric band-shaped regions with low film thickness, and changes a Gaussian beam into a flat-top beam.

Special Publication No. 7-102470 JP 2002-98930 A

In the various apodizing filters described above, a distribution of thickness or density is imparted, and therefore, during the manufacturing process, a mask adjusted in accordance with the distribution is required, making the manufacturing process complicated.
Furthermore, among the various apodizing filters mentioned above, those that adjust the cross-sectional intensity distribution by partially absorbing the beam using a thin metal film such as aluminum accumulate the energy of the beam through absorption, resulting in a relatively short lifespan and a low resistance to high-power lasers, making them susceptible to damage.

SUMMARY OF THE PRESENT EMBODIMENTS It is therefore a primary object of the present invention to provide an optical thin film filter and beam shaper which are easy to manufacture.
Another main object of the present invention is to provide an optical thin film filter or beam shaper which has a long life and is capable of converting the cross-sectional intensity distribution of a high-power laser beam in a highly durable state.

In order to achieve the above object, the present invention provides an optical thin film filter comprising a substrate and an optical multilayer film formed on a surface of the substrate, the optical multilayer film having an incident angle-dependent transmittance which is a transmittance according to the incident angle of a light beam at a wavelength of the light beam incident on the optical multilayer film due to interference, and converting a cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance ,
The optical multilayer film is characterized in that the ellipticity change, which is the amount of change between the ellipticity of the electric field of the light ray before it is incident on the optical multilayer film and the ellipticity of the electric field of the light ray whose cross-sectional intensity distribution has been converted by the optical multilayer film, is 0.5 or less .
The invention described in claim 2 comprises a substrate and an optical multilayer film formed on a surface of the substrate, the optical multilayer film having an incident angle-dependent transmittance, which is a transmittance according to the incident angle of a light beam at the wavelength of the light beam incident on the optical multilayer film due to interference, and converting a cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance, characterized in that the cross-sectional intensity distribution of the light beam before it is incident on the optical multilayer film is a Gaussian type, and the cross-sectional intensity distribution of the light beam converted by the optical multilayer film is a flat-top type.
The invention described in claim 3 comprises a substrate and an optical multilayer film formed on the surface of the substrate, the optical multilayer film having an incident angle-dependent transmittance, which is a transmittance according to the incident angle of a light beam at the wavelength of the light beam incident on the optical multilayer film due to interference, and converting the cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance, characterized in that the cross-sectional intensity distribution of the light beam before it is incident on the optical multilayer film is a flat-top type, and the cross-sectional intensity distribution of the light beam converted by the optical multilayer film is a donut type.

In order to achieve the above object, the invention described in claim 4 is a beam shaper comprising the above optical thin film filter and one or more lenses, wherein at least one of the lenses refracts the light beam and makes it incident on the optical thin film filter.
The invention described in claim 5 is characterized in that in the above invention, at least one of the optical thin film filter and the one or more lenses is housed in a case.
The invention described in claim 6 is characterized in that, in the above invention, a pinhole plate having a pinhole is provided upstream of the light beam from the optical thin film filter, and at least one of the lenses focuses the light beam at the pinhole.
The invention described in claim 7 is characterized in that, in the above invention, some or all of the multiple lenses are arranged upstream of the light beam from the optical thin film filter, thereby expanding the diameter of the light beam.
The invention described in claim 8 is characterized in that, in the above invention, instead of the optical thin film filter and one of the lenses, a single lens on which the optical multilayer film is formed is arranged.

Therefore, a major advantage of the present invention is that it provides an optical thin film filter and beam shaper that is easy to manufacture.
Another main effect of the present invention is to provide an optical thin film filter and beam shaper which has a long life and can perform cross-sectional intensity distribution conversion of a high-power laser beam in a highly durable state.

1A is a schematic diagram of a beam shaper according to a first embodiment of the present invention, FIG. 1B is a schematic diagram of a modified example of the beam shaper, FIG. 1C is a schematic graph and a formula of a Gaussian cross-sectional intensity distribution of a beam (the horizontal axis is the distance d from the optical axis, and the vertical axis is the relative intensity), and FIG. 1D is a schematic graph and a formula of a flat-top cross-sectional intensity distribution of a beam. 1A is a schematic diagram of a beam shaper according to a second embodiment of the present invention, and FIG. 1B is a schematic diagram of a modified example of a part of the beam shaper. 13A is a schematic diagram of a beam shaper according to a third embodiment of the present invention, and FIG. 13B is a schematic diagram of a modified example of a part of the beam shaper. FIG. 13A is a schematic diagram of a beam shaper according to a fourth embodiment of the present invention, and FIG. 13B is a schematic diagram of a modified example of a part of the beam shaper. 3 is a graph showing the physical film thickness of each layer of the optical multilayer film according to Example 1 of the present invention. 4 is a graph showing the physical film thickness of each layer of the antireflection film according to Example 1 of the present invention. FIG. 2 is a schematic diagram of a lens and an optical thin film filter according to the first embodiment of the present invention, viewed from above the lens, in the case where the beam is linearly polarized. FIG. 2 is a schematic diagram of a lens and an optical thin film filter according to the first embodiment of the present invention, viewed from above the lens, in the case where the beam is circularly polarized. FIG. 1 is a schematic diagram relating to ellipticity. 1 is a graph showing the spectral transmittance distribution of the optical multilayer film of Example 1 when a beam is incident at an angle θ=0° at each wavelength in a wavelength range including 1064 nm. 1 is a graph showing the target transmittance value T(θ), the transmittance T _p for p-polarized light, the transmittance T _s for s-polarized light, and the phase difference Δ (vertical axis) when a beam with a wavelength of 1064 nm is incident on the optical multilayer film of Example 1 at an angle θ (horizontal axis). 1 is a graph showing the relationship between spatial coordinates (horizontal axis) and the target transmittance value T(θ), the transmittance _Tp for p-polarized light, the transmittance _Ts for s-polarized light, and the angle of incidence θ (vertical axis) for a beam with a wavelength of 1064 nm for the optical multilayer coating 8 of Example 1. Graphs (A) to (C) show cross-sectional intensity distributions and ellipticity distributions of a linearly polarized beam in a plane with azimuth angles φ of 0°, 45°, and 90°, respectively, versus spatial coordinates, before and after conversion in Example 1, and for a target value. This is a schematic diagram in which a cross section of a beam viewed in the direction in which the beam travels is superimposed with a specific axis and point in polar coordinates (d, φ). 15A is a graph showing the trajectory of the electric field vector of a linearly polarized beam at point (0,0) shown in FIG. 14 before and after transformation in Example 1, and FIGS. 15B to 15F are graphs showing the trajectories of the electric field vector of a linearly polarized beam at points (2,0), (2,22.5), (2,45), (2,67.5), and (2,90), respectively, before and after transformation in Example 1. Graphs (A) to (E) show the trajectories of the electric field vector of a linearly polarized beam at points (4,0), (4,22.5), (4,45), (4,67.5), and (4,90), respectively, before and after transformation in Example 1. Graphs (A) to (E) show the trajectories of the electric field vectors of a linearly polarized beam at points (10,0), (10,22.5), (10,45), (10,67.5), and (10,90), respectively, before and after conversion by the optical multilayer film 8 of Example 1. 13A-13C are graphs similar to those of FIGS. 13A-13C for the conversion according to Example 1 for a circularly polarized beam. 16 is a graph similar to FIG. 15 for the conversion according to Example 1 for a circularly polarized beam; 17 is a graph similar to FIG. 16 for the conversion according to Example 1 for a circularly polarized beam. 18 is a graph similar to FIG. 17 for the conversion according to Example 1 for a circularly polarized beam; FIG. 6 is a view similar to FIG. 5 according to a second embodiment of the present invention. FIG. 10 is a view similar to FIG. 10 according to a second embodiment of the present invention. FIG. 11 is a view similar to FIG. 11 according to a second embodiment of the present invention. FIG. 13 is a view similar to FIG. 12 according to a second embodiment of the present invention. FIG. 13 is a view similar to FIG. 13 but relating to Example 2 (linearly polarized light) of the present invention. FIG. 15 is a view similar to FIG. 15 but relating to Example 2 (linearly polarized light) of the present invention. FIG. 16 is a view similar to FIG. 16 but relating to Example 2 (linearly polarized light) of the present invention. FIG. 17 is a view similar to FIG. 17 but relating to Example 2 (linearly polarized light) of the present invention. FIG. 18 is a view similar to FIG. 18 but relating to Example 2 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 19 relating to Example 2 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 20 but relating to Example 2 (circularly polarized light) of the present invention. FIG. 21 is a view similar to FIG. 21 relating to Example 2 (circularly polarized light) of the present invention. FIG. 7 is a view similar to FIG. 5 according to a third embodiment of the present invention. FIG. 10 is a view similar to FIG. 10 but relating to a third embodiment of the present invention. FIG. 11 is a view similar to FIG. 11 according to a third embodiment of the present invention. FIG. 12 is a view similar to that of FIG. 12 according to a third embodiment of the present invention. FIG. 13 is a view similar to FIG. 13 but relating to Example 3 (linearly polarized light) of the present invention. FIG. 15 is a view similar to FIG. 15 but relating to Example 3 (linearly polarized light) of the present invention. FIG. 16 is a view similar to FIG. 16 but relating to Example 3 (linearly polarized light) of the present invention. FIG. 17 is a view similar to FIG. 17 but relating to Example 3 (linearly polarized light) of the present invention. FIG. 18 is a view similar to FIG. 18 but relating to Example 3 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 19 relating to Example 3 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 20 but relating to Example 3 (circularly polarized light) of the present invention. FIG. 21 is a view similar to FIG. 21 but relating to Example 3 (circularly polarized light) of the present invention. FIG. 10 is a view similar to FIG. 5 according to a fourth embodiment of the present invention. FIG. 7 is a view similar to FIG. 6 according to a fourth embodiment of the present invention. FIG. 10 is a view similar to FIG. 10 but relating to a fourth embodiment of the present invention. FIG. 11 is a view similar to FIG. 11 according to a fourth embodiment of the present invention. FIG. 12 is a view similar to that of FIG. 12 according to a fourth embodiment of the present invention. FIG. 13 is a view similar to FIG. 13 but relating to Example 4 (linearly polarized light) of the present invention. FIG. 15 is a view similar to FIG. 15 but relating to Example 4 (linearly polarized light) of the present invention. FIG. 16 is a view similar to FIG. 16 but relating to Example 4 (linearly polarized light) of the present invention. FIG. 17 is a view similar to FIG. 17 but relating to Example 4 (linearly polarized light) of the present invention. FIG. 18 is a view similar to FIG. 18 but relating to Example 4 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 19 relating to Example 4 (circularly polarized light) of the present invention. FIG. 20 is a view similar to FIG. 20 but relating to Example 4 (circularly polarized light) of the present invention. FIG. 21 is a view similar to FIG. 21 but relating to Example 4 (circularly polarized light) of the present invention. FIG. 7 is a view similar to FIG. 5 according to a fifth embodiment of the present invention. FIG. 10 is a view similar to that of FIG. 10 according to a fifth embodiment of the present invention. FIG. 11 is a view similar to that of FIG. 11 according to a fifth embodiment of the present invention. FIG. 12 is a view similar to that of FIG. 12 according to a fifth embodiment of the present invention. FIG. 13 is a view similar to FIG. 13 but relating to Example 5 (linearly polarized light) of the present invention. FIG. 52 is a view similar to FIG. 52 relating to Example 5 of the present invention (linearly polarized light). FIG. 53 is a view similar to FIG. 53 relating to Example 5 of the present invention (linearly polarized light). FIG. 18 is a view similar to FIG. 18 relating to Example 5 (circularly polarized light) of the present invention. FIG. 57 is a view similar to FIG. 56 relating to Example 5 of the present invention (circularly polarized light). FIG. 57 is a view similar to FIG. 57 relating to Example 5 of the present invention (circularly polarized light).

Below, examples of embodiments of the present invention will be described with reference to the drawings as appropriate. Note that the present invention is not limited to these examples.

[First form]
FIG. 1A is a schematic diagram of a beam shaper 1 according to a first embodiment of the present invention.
The beam shaper 1 includes a lens 2 and an optical thin film filter 4 .
The beam shaper 1 converts the cross-sectional intensity distribution of the beam B. The cross-sectional intensity distribution of the beam B is an energy distribution in a cross section perpendicular to the traveling direction of the beam B. Note that the target of the cross-sectional intensity distribution conversion may be a light beam other than the beam B from a laser oscillator.
The beam shaper 1 is disposed adjacent to a table on which a workpiece WO is placed in the laser processing apparatus.
The beam B is emitted from a laser oscillator provided in the laser processing apparatus in a lateral direction, and is redirected by a mirror toward the lens 2 (vertical direction) to enter the lens 2 from above.
The beam shaper 1 may be disposed away from the workpiece WO (table). At least one of various directions of the beam B, such as the direction of emission from the laser oscillator and the direction after reflection by a mirror, may be different from the directions described above or shown in the figure. The beam shaper 1 may be provided in a device other than the laser processing device.

The lens 2 is a convex lens, and in this embodiment is a plano-convex lens having a convex surface and a flat surface. A plano-convex lens is preferable because it is easy to arrange the plate-shaped optical thin film filter 4 on the flat surface side.
The lens 2 is translucent and refracts a beam B having a wavelength λ and a beam diameter 2D (diameter) that is incident on the lens 2, causing the beam to converge at a focal point F, which is a point on the optical axis L separated by a focal length f.
The central axis of the beam B and the optical axis L of the lens 2 coincide with each other.
The material of the lens 2 is not particularly limited, and may be, for example, glass, crystal, or resin.

Beam B is incident on the convex surface of lens 2, and is bent at an angle θ due to the shape of the convex surface that is the interface, such that it converges at focal point F. Angle θ is the angle of the bent portion of beam B with respect to optical axis L. Angle θ changes with distance d from optical axis L, and θ=0 when d=0, and θ increases as d increases, reaching a maximum value _θmax when d=D (radius of beam B). In other words, angle θ is a function θ(d) of distance d. Concentric circular portions (portions where distance d is constant) in the cross section of beam B are bent at the same angle θ.
From the viewpoint of ensuring the maximum value θ _max of the angle θ as large as possible and allowing some margin in the design of the optical multilayer film 8, it is preferable that the lens 2 has a relatively short focal length f, for example, a focal length f shorter than the diameter of the lens 2.
Furthermore, from a geometrical relationship, θ(d) and θ _max are expressed by the following expressions (1) and (2), respectively: where tan ⁻¹ is the inverse function of tan.

The optical thin film filter 4 includes a substrate 6 , an optical multilayer film 8 , and an anti-reflection film 10 .
The substrate 6 is in the form of a plate, and has a first surface R1 on which an optical multilayer film 8 is formed, and a second surface R2 on which an anti-reflection film 10 is formed.
The base material 6 is light-transmitting.
The material of the base material 6 is not particularly limited, and may be, for example, glass such as quartz glass, crystal, or resin.
The shape of the substrate 6 is not particularly limited, and may be, for example, a parallel plate or a wedge.
The thickness of the base material 6 is not particularly limited, but is preferably thin from the viewpoint of suppressing aberration. However, it is preferable that the strength of the base material 6 is at least a minimum level.
1B, the optical thin film filter 4 may be made of only an optical multilayer film 8 and attached to the surface R' (the flat surface of a plano-convex lens) of the lens 2. In this case, the lens 2 is dedicated to the attached optical thin film filter 4, while aberration caused by the optical thin film filter 4 is suppressed to a minimum.

The optical multilayer film 8 is an inorganic multilayer film using a dielectric material or a semiconductor material, and is a dielectric multilayer film or a semiconductor multilayer film.
The optical multilayer film 8 is formed on a part or the whole of the first surface R1 of the substrate 6. The optical multilayer film 8 may be formed on both the first surface R1 and the second surface R2.
The optical multilayer film 8 includes a low refractive index layer and a high refractive index layer, and may further include a medium refractive index layer.
The design of the optical multilayer film 8 can be changed by changing design factors such as the number and materials of the high and low refractive index layers (as well as the medium refractive index layers), and increasing or decreasing the thickness of each layer (the physical film thickness or optical film thickness of the layer).
For example, a part or all of the structure in the optical multilayer film 8 may be replaced with another optically equivalent structure, such as replacing a medium refractive index layer with a combination of a high refractive index layer and a low refractive index layer that are optically equivalent thereto.

The high refractive index layer is _formed from a high refractive index material such as zirconium oxide ( _ZrO2 ), titanium oxide ( _TiO2 ), tantalum oxide ( _Ta2O5 ), niobium oxide ( _Nb2O5 ), hafnium oxide ( _HfO2 ), _lanthanum oxide ( _La2O3 ), silicon ( _Si ), or _praseodymium oxide ( _Pr2O3 ), or a mixture of two or more of these.
The low refractive index layer is formed from a low refractive index material such as silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), calcium fluoride (CaF ₂ ), magnesium fluoride (MgF ₂ ), a combination of aluminum oxide and praseodymium oxide (Al ₂ O ₃ -Pr ₂ O ₃ ), a combination of aluminum oxide and lanthanum oxide (Al ₂ O ₃ -La ₂ O ₃ ), or a combination of aluminum oxide and tantalum oxide (Al ₂ O ₃ -Ta ₂ O ₅ ), or a mixture of two or more of these.
The medium refractive index layer is made of a medium refractive index material such as Al ₂ O ₃ , Pr ₂ O ₃ , La ₂ O ₃ , Al ₂ O ₃ --Pr ₂ O ₃ , or Al ₂ O ₃ --La ₂ O ₃ .
For example, two materials may be selected from the above-mentioned high refractive index materials to form the optical multilayer film 8. In addition, a film having another function, such as an antifouling film, may be combined with the outside of the optical multilayer film 8.

The low and high refractive index layers (as well as the medium refractive index layer) of the optical multilayer film 8 are formed by vacuum deposition, ion-assisted deposition, ion plating, sputtering or the like.
The optical multilayer film 8 may be formed on a plurality of surfaces of the substrate 6. For example, the optical multilayer film 8 may be formed on both the front and back surfaces of the substrate 6 that is a parallel plate or a wedge, or has a concave or convex surface.

The antireflection coating 10 is a film mainly including low refractive index layers and high refractive index layers alternately stacked together, similar to the optical multilayer coating 8. The antireflection coating 10 is designed to suppress reflection of the beam B at the second surface R2.
The anti-reflection film 10 is formed on a part or the entirety of the second surface R2 of the substrate 6.
The anti-reflection film 10 may be formed on the first surface R1 and the second surface R2. The anti-reflection film 10 may be omitted.

The optical thin film filter 4 is disposed on the exit side of the lens 2 from which the beam B emerges, i.e., on the flat surface side of the lens 2. The optical thin film filter 4 is disposed so that the optical multilayer film 8 is closer to the lens 2 in order to allow the beam B to be directly incident on the optical multilayer film 8 without passing through the substrate 6. The optical thin film filter 4 may also be disposed so that the substrate 6 is closer to the lens 2.
The beam B having an angle θ(d) is incident on the optical multilayer film 8 by the lens 2. Therefore, the angle θ corresponds to the angle of incidence.

The cross-sectional intensity distribution of beam B from the laser oscillator to just before it is incident on the optical multilayer film 8 is a Gaussian type as shown in Figure 1 (C), in which the intensity of beam B is strongest at the center of the circular cross section of beam B, the intensity weakens concentrically from the center, and the intensity is sufficiently small at the outer edge of beam B.
This Gaussian cross-sectional intensity distribution f _G (d) is generally expressed by the following equation (3), where the strongest intensity is 1: where σ is the standard deviation, and the full width at half maximum FWHM of f _G (d) is 2√(2ln2)σ, where ln is the natural logarithm.

The optical multilayer film 8 is designed so that the transmittance changes in a predetermined manner according to the angle θ at which the beam B is incident.
In general, the optical multilayer film 8 that filters light has a characteristic that the spectral transmittance distribution shifts to the short wavelength side as the angle of incidence θ of light increases. That is, in the optical multilayer film 8, the interference state in the multilayer differs depending on the angle of incidence θ, and the interference depends on the angle of incidence θ, so that the transmittance depends on the angle of incidence θ (incident angle-dependent transmittance).
For example, in a short wave pass filter having a transmittance close to 100% on the shorter wavelength side and a transmittance close to 0% on the longer wavelength side at θ=0 (normal incidence), with the wavelength of 700 nm as the boundary, as θ increases, the spectral transmittance distribution shifts to the shorter wavelength side, so that the wavelength shorter than 700 nm is the boundary, and the transmittance is close to 100% on the shorter wavelength side and the transmittance is close to 0% on the longer wavelength side.
Conventionally, such characteristics have been focused on in the wavelength axis (horizontal axis) direction, whereas the present invention focuses on the change in the transmittance axis (vertical axis) direction and controls the change to configure an optical multilayer film 8 having a desired transmittance that depends on the angle of incidence θ.
When the transmittance of the optical multilayer film 8 is less than 100%, the transmittance is reduced mainly by reflection of a portion of the beam B. In the optical multilayer film 8, absorption of the beam B hardly occurs and does not contribute to a decrease in the transmittance.

The optical multilayer coating 8 is designed to have a transmittance with angle θ such that the cross-sectional intensity distribution of the beam B is converted from a Gaussian cross-sectional intensity distribution _fG (d) to a flat-top cross-sectional intensity distribution _fF (d) (flat-top with tail: Examples 1, 2, and 4 described below, flat-top cut-tail: Example 3 described below). Note that the optical multilayer coating 8 may convert the cross-sectional intensity distribution from a Gaussian type to a type other than the flat-top type, or from a type other than the Gaussian type to a flat-top type or other type (conversion from a flat-top cut-tail type to a doughnut type: Example 5 described below).
More specifically, the flat-top cross-sectional intensity distribution f _F (d) is a distribution in which the portion exceeding half-value (the portion above the full width at half maximum FWHM line) in the Gaussian cross-sectional intensity distribution f _G (d) is cut, and is expressed by the following formula (4). This cut forms a circular flat portion (when the cross-sectional intensity distribution is three-dimensional) with the full width at half maximum FWHM as a diameter, and this flat portion becomes an effective cross-sectional area that effectively acts on the workpiece WO etc. in terms of the intensity of the beam B. The flat-top cross-sectional intensity distribution f _F (d) may be modified in various ways, for example, to a distribution in which the portion exceeding 2/3 is cut.

The target value T(θ) of the transmittance for each angle θ of the optical multilayer film 8 is calculated by the following formula (5) based on the cross-sectional intensity distributions f _G (d) and f _F (d) of each type.
The optical multilayer film 8 is designed to match a target transmittance value T(θ), and ideally, the transmittance T _r (θ) according to the angle θ is exactly the same as the target value T(θ) (T _r (θ)=T(θ)). In reality, the optical multilayer film 8 is designed so that the transmittance T _r (θ) approaches the target value T(θ) as close as possible.

As beam B passes through optical multilayer film 8 having transmittance T _r (θ), the cross-sectional intensity distribution of beam B is converted from a Gaussian type to a flat-top type, and beam B reaches workpiece WO while its cross-sectional intensity distribution shrinks similarly due to the converging action of lens 2.
Strictly speaking, in the first embodiment in which the optical thin film filter 4 is disposed, the beam B is refracted by the optical thin film filter 4 (mainly the substrate 6), and therefore the outer edge of the beam B is shifted, compared to the outer edge of the beam B (the dotted line of the beam B below the optical thin film filter 4 in FIG. 1) when the optical thin film filter 4 is not disposed and only the lens 2 is used. Note that in FIG. 1, the shift in the outer edge of the beam B is exaggerated for clarity.
In reality, the deviation of the outer edge of the beam B is proportional to the thickness of the optical thin film filter 4, and if the optical thin film filter 4 (substrate 6) is a thin plate, the deviation is sufficiently small, so the workpiece WO may be placed at a position away from the lens 2 by the focal length f, as in the case where the optical thin film filter 4 is not placed. Also, when precision is important, or when the optical thin film filter 4 is relatively thick to ensure strength, etc., the deviation of the outer edge of the beam B may be calculated, and the position of the workpiece WO may be shifted by the amount of the deviation. The calculation of the deviation is similar when the substrate 6 is placed on the lens 2 side. In the case of the modified example shown in FIG. 1(B), the lens 2 with the optical multilayer film 8 suppresses the occurrence of various aberrations, and can be handled in the same manner as the lens 2 without the optical multilayer film 8 in terms of placement, etc.
A workpiece WO is processed by a beam B which is focused and whose cross-sectional intensity distribution is converted into a flat-top type.

The optical thin film filter 4 of the first form comprises a substrate 6 and an optical multilayer film 8 formed on the surface R of the substrate 6. The optical multilayer film 8 has an incident angle-dependent transmittance T _r (θ) (design target value T(θ)) at the wavelength of the beam B incident on the optical multilayer film 8 due to interference, which is a transmittance according to the angle of incidence θ of the beam B. The optical multilayer film 8 converts the cross-sectional intensity distribution of the beam B refracted and incident on the optical multilayer film 8 by using this incident angle-dependent transmittance.
Therefore, the optical thin film filter 4 can be manufactured simply by forming the optical multilayer film 8 on the substrate 6, and an optical thin film filter 4 that is easy to manufacture is provided.
In addition, the optical multilayer film 8 reduces the transmittance by reflection, so the energy of the beam B is not accumulated in the optical multilayer film 8 itself. Therefore, the optical thin film filter 4 has a long life, is highly resistant to high-power lasers, and is prevented from being damaged.

Furthermore, in the first form of optical thin film filter 4, the ellipticity change amount, which is the amount of change between the ellipticity k of the electric field of beam B before it is incident on the optical multilayer film 8 and the ellipticity k of the electric field of beam B whose cross-sectional intensity distribution has been converted by the optical multilayer film 8, is 0.5 or less. Therefore, the polarization state is preserved before and after the conversion, and an optical thin film filter 4 is provided which converts the cross-sectional intensity distribution of circularly polarized beam B, which is particularly suitable for processing, into a state that remains circularly polarized or is close to circularly polarized.
Furthermore, the cross-sectional intensity distribution of the beam B before it is incident on the optical multilayer film 8 is a Gaussian type, and the cross-sectional intensity distribution of the beam B converted by the optical multilayer film 8 is a flat-top type. Therefore, an optical thin-film filter 4 is provided which converts a typical Gaussian type cross-sectional intensity distribution immediately after oscillation into a flat-top type suitable for thick plate processing, is easy to manufacture, has a long life, and is capable of handling high power.
In addition, the beam shaper 1 of the first embodiment includes an optical thin-film filter 4 and one lens 2, and the lens 2 refracts the beam B and makes it incident on the optical thin-film filter 4. Thus, there is provided an easily manufactured and highly durable beam shaper 1 including the lens 2 that makes the beam B incident on the optical thin-film filter 4 at various angles of incidence θ.

[Second embodiment]
FIG. 2A is a schematic diagram of a beam shaper 101 according to a second embodiment of the present invention.
The beam shaper 101 includes a lens 2 and an optical thin film filter 4 similar to those in the first embodiment.
The convex surface of the lens 2 is disposed on the workpiece WO side. The substrate 6 of the optical thin film filter 4 is disposed opposite the flat surface of the lens 2.
As shown in Fig. 2(B), the lens 2 and the optical thin film filter 4 can be replaced with the lens 2 and an optical multilayer film 8 formed on the plane of the lens 2. In this case, the same effects as those of the first embodiment shown in Fig. 1(B) are achieved. The second embodiment also has the same modified examples as the first embodiment, as appropriate.

The beam shaper 101 also includes a lens 102 .
The lens 102 is configured similarly to the lens 2. The focal length f of the lens 102 is the same as that of the lens 2.
The lens 102 is disposed at a position twice the focal length f away from the lens 2 with its flat surface facing the flat surface of the lens 2. The lens 102 is disposed on the opposite side of the workpiece WO from the lens 2. The lens 102 is disposed upstream of the lens 2 and the optical thin film filter 4 in the optical path of the beam B.

Furthermore, the beam shaper 101 includes a lens 112 .
The lens 112 is a convex lens, here a plano-convex lens.
The focal length f′ of the lens 112 is sufficiently larger than the focal length f of the lenses 2 and 102 (for example, at least twice as large).
The convex surface of lens 112 faces the convex surface of lens 2 and is adjacent to the convex surface of lens 2 .
The optical axes L of the lenses 2, 102, and 112 are aligned and coincide with the central axis of the beam B.

The lenses 2, 102, 112 and the optical thin film filter 4 are disposed in a case 120. The case 120 has an upper hole 121 for admitting the beam B on the lens 102 side, and a lower hole 122 for issuing the beam B on the lens 112 side. A light-transmitting window plate may be provided in the lower hole 122 to prevent debris from the workpiece WO from entering the case 120.
A pinhole plate 124 is disposed within the case 120. The pinhole plate 124 is disposed so as to be perpendicular to the optical axis L. The pinhole plate 124 has a pinhole PH. The pinhole plate 124 is disposed midway between the lenses 2 and 102. The distances of the pinhole plate 124 to the lenses 2 and 102 are equal to each other. The pinhole PH is disposed on the optical axis L.

The Gaussian beam B entering through the upper hole 121 is converged by the lens 102, forms a focal point F' at the pinhole PH, diverges downward, and enters the optical multilayer film 8 with an incident angle θ corresponding to the distance d from the optical axis L.
The beam B is converted into a flat-top beam by the optical multilayer film 8 , exits the optical multilayer film 8 and the substrate 6 , and reaches the lens 2 .
The diverging beam B is returned to a parallel state by lens 2 and reaches lens 112 .
The beam B is converged by the lens 112 while maintaining a flat-top cross-sectional intensity distribution, exits the pilot hole 122, and is directed to a workpiece WO that is a focal length f' away.
A workpiece WO is processed by a beam B which is focused and whose cross-sectional intensity distribution is converted into a flat-top type.

The beam shaper 101 of the second embodiment includes an optical thin-film filter 4 and three lenses 2, 102, and 112, and the lens 102 refracts the beam B and makes it incident on the optical thin-film filter 4. Thus, there is provided an easily manufactured and highly durable beam shaper 101 including the lens 102 that makes the beam B incident on the optical thin-film filter 4 at various angles of incidence θ.
In the second form of beam shaper 101, the optical thin film filter 4 and the three lenses 2, 102, and 112 are housed in a case 120. This prevents the scattered light of the beam B, including the reflected light from the optical multilayer film 8, from being emitted outside the case 120, and suppresses the influence of the scattered light on the laser oscillator and the like (external devices and the like).
Furthermore, in the second form of beam shaper 101, a pinhole plate 124 having a pinhole PH is provided upstream of the optical thin film filter 4 in the beam B, and the lens 102 focuses the beam B at the pinhole PH (focal point F'). Thus, the pinhole plate 124 prevents the scattered light from returning to the upstream side of the beam B, suppressing the occurrence of effects of the scattered light on the laser oscillator, etc. Also, the lens 112 for converging the beam B on the workpiece WO can be a lens with a medium focal length or longer that is less expensive than the lens 2 with a short focal length.

[Third Form]
FIG. 3A is a schematic diagram of a beam shaper 201 according to a third embodiment of the present invention.
The beam shaper 201 includes a lens 202 and an optical thin film filter 4 similar to that of the first embodiment.
The lens 202 is a convex lens, and is a plano-convex lens. The flat surface of the lens 202 is disposed on the workpiece WO side. The optical multilayer film 8 of the optical thin film filter 4 is disposed opposite the flat surface of the lens 202.
The focal length _f3 of lens 202 is longer than the focal length f of lens 2 of the first embodiment.
As shown in Fig. 3B, the lens 202 and the optical thin film filter 4 can be replaced with a lens 202 and an optical multilayer film 8 formed on the plane of the lens 202. In this case, the same effects as those of the first embodiment shown in Fig. 1B can be achieved. The third embodiment also has the same modifications as the first and second embodiments, as appropriate.

The beam shaper 201 also includes a lens 212 .
The lens 212 is a concave lens, and in this embodiment is a plano-concave lens having a concave surface and a flat surface. The focal length _f1 of the lens 212 is a negative value. The oscillated beam B is incident on the concave surface of the lens 212 and diverges from the flat surface of the lens 212. The lens 212 expands the diameter of the beam B. The lens 212 may be a biconcave lens or the like.
The lens 212 is disposed upstream of the lens 202. The flat surface of the lens 212 is disposed on the lens 202 side.

Furthermore, the beam shaper 201 includes a lens 222 .
The lens 222 is a convex lens, here a plano-convex lens.
The focal length _f2 of the lens 222 is greater than the absolute value of the focal length _f1 of the lens 212.
The lens 222 is disposed between the lenses 212 and 202 and on the side closer to the lens 202. The lens 222 is adjacent to the lens 202. The convex surface of the lens 222 faces the convex surface of the lens 202.
The divergent light from the lens 212 that is incident on the flat surface of the lens 222 becomes parallel light on the convex surface.
The optical axes L of the lenses 202, 212, and 222 are aligned and coincide with the central axis of the beam B.
The combination of lenses 212 and 222 is of the Galilean type.

The lenses 202, 212, 222 and the optical thin film filter 4 are arranged in a case 230. The case 220 has an upper hole 231 for admitting the beam B on the lens 212 side, and a lower hole 232 for issuing the beam B on the lens 112 side. A light-transmitting window plate may be installed in the lower hole 232 to prevent debris from the workpiece WO from entering the case 220.

The Gaussian beam B entering from the upper hole 231 diverges by the lens 212, becomes a parallel beam with a larger diameter by the lens 222, converges by the lens 202, and enters the optical multilayer film 8 with an incident angle θ corresponding to the distance d from the optical axis L.
The beam B is converted to a flat-top beam by the optical multilayer film 8, exits the optical multilayer film 8 and the substrate 6, exits the pilot hole 232, and is directed to the workpiece WO that is a focal length _f3 away from the lens 202.
A workpiece WO is processed by a beam B which is focused and whose cross-sectional intensity distribution is converted into a flat-top type.

The beam shaper 201 of the third embodiment includes an optical thin-film filter 4 and three lenses 202, 212, and 222, and the lens 202 refracts the beam B and makes it incident on the optical thin-film filter 4. Thus, there is provided an easily manufactured and highly durable beam shaper 201 including the lens 202 that makes the beam B incident on the optical thin-film filter 4 at various angles of incidence θ.
In the third embodiment of the beam shaper 201, the optical thin film filter 4 and the three lenses 202, 212, and 222 are housed in a case 230. This prevents the scattered light of the beam B, including the reflected light from the optical multilayer film 8, from being emitted outside the case 230, and suppresses the effect of the scattered light on the laser oscillator, etc.
Furthermore, in the beam shaper 201 of the third embodiment, the multiple lenses 212, 222 are disposed upstream of the beam B from the optical thin film filter 4, and expand the diameter of the beam B. Therefore, the expanded beam B is incident on the lens 202 for making the beam B incident on the optical multilayer film 8 at an angle θ, and even if a lens 202 with a medium focal length or longer that is less expensive than the lens 2 with a short focal length is used, the beam B is incident with the width of the angle θ being sufficiently secured (the maximum value θ _max of the angle θ is sufficiently large), so that even if a lens 202 with a medium focal length or longer is used, the optical multilayer film 8 can be designed with some leeway.

[Fourth Form]
FIG. 4A is a schematic diagram of a beam shaper 301 according to a fourth embodiment of the present invention.
The beam shaper 301 is similar to the third embodiment except that the Galilean lenses 212, 222 in the third embodiment are replaced by Keplerian lenses 312, 222 and a pinhole plate 334 is further added.
That is, the beam shaper 301 has a lens 312 having a convex surface on the upstream side on the upper hole 231 side, instead of the lens 212 having a concave surface on the upstream side of the third embodiment.
The lens 312 is a convex lens, which is a plano-convex lens, and has a focal length f ₁ ' which differs from the focal length f ₁ of the lens 212 only in positive and negative sign. The lens 312 may be a biconvex lens or the like.

The optical axes L of the lenses 202, 222, and 312 are aligned and coincide with the central axis of the beam B.
Beam B incident on the convex surface of lens 312 exits the plane as converging light, forms a focal point F'', and then diverges to reach lens 222. Lens 312 expands the diameter of beam B at a distance farther than focal length f ₁ '.
A pinhole plate 334 is disposed within the case 230. The pinhole plate 334 is disposed so as to be perpendicular to the optical axis L. The pinhole plate 334 has a pinhole PH. The pinhole plate 334 is disposed midway between the lenses 222 and 312. The pinhole PH is disposed so as to include a focal point F″ on the optical axis L.
As shown in Fig. 4(B), the lens 202 and the optical thin film filter 4 can be replaced with a lens 202 and an optical multilayer film 8 formed on the plane of the lens 202. In this case, the same effects as those of the first embodiment shown in Fig. 1(B) are achieved. The fourth embodiment also has the same modifications as the first to third embodiments as appropriate.

The Gaussian beam B entering from the upper hole 231 is converged and then diverged by the lens 312, expanded in diameter by the lens 222 to become parallel light, converged by the lens 202, and incident on the optical multilayer film 8 with an incident angle θ corresponding to the distance d from the optical axis L.
The beam B is converted to a flat-top beam by the optical multilayer film 8, exits the optical multilayer film 8 and the substrate 6, exits the pilot hole 232, and is directed to the workpiece WO that is a focal length _f3 away from the lens 202.
A workpiece WO is processed by a beam B which is focused and whose cross-sectional intensity distribution is converted into a flat-top type.

The beam shaper 301 of the fourth embodiment includes an optical thin-film filter 4 and three lenses 202, 222, and 312, and the lens 202 refracts the beam B and makes it incident on the optical thin-film filter 4. Thus, there is provided an easily manufactured and highly durable beam shaper 301 including the lens 202 that makes the beam B incident on the optical thin-film filter 4 at various angles of incidence θ.
In the fourth embodiment of the beam shaper 301, the optical thin film filter 4 and the three lenses 202, 222, and 312 are housed in the case 230. This prevents the scattered light of the beam B, including the reflected light from the optical multilayer film 8, from being emitted outside the case 230, and suppresses the effect of the scattered light on the laser oscillator, etc.
Furthermore, in the fourth form of beam shaper 301, a pinhole plate 334 having a pinhole PH is provided upstream of the optical thin film filter 4 in the direction of beam B, and the lens 312 focuses the beam B at the pinhole PH (focal point F"). Thus, the pinhole plate 334 prevents the scattered light from returning to the upstream side of the beam B, suppressing the occurrence of effects of the scattered light on the laser oscillator, etc. Also, the lens 202 for converging the beam B on the workpiece WO can be one with a medium focal length or longer that is less expensive than the lens 2 with a short focal length.
Furthermore, in the beam shaper 301 of the fourth embodiment, the multiple lenses 222, 312 are disposed upstream of the optical thin film filter 4 with respect to the beam B, and expand the diameter of the beam B. Therefore, the expanded beam B is incident on the lens 202 for making the beam B incident on the optical multilayer film 8 at an angle θ, and even if a lens 202 with a medium focal length or longer that is less expensive than the lens 2 with a short focal length is used, the beam B is incident with the width of the angle θ being sufficiently secured, so that even if the lens 202 with a medium focal length or longer is used, the optical multilayer film 8 can be designed with some leeway.

In the modified examples present in all of the first to fourth forms described above (Figures 1(B), 2(B), 3(B), and 4(B)), instead of the optical thin-film filter 4 and one lens (first and second forms: lens 2, third and fourth forms: lens 202), a single lens having an optical multilayer film 8 formed on its surface R' (first and second forms: lens 2, third and fourth forms: lens 202) is arranged.
In this case, the aberration caused by the optical thin film filter 4 capable of changing the cross-sectional intensity distribution of the beam B is suppressed to a minimum.

Next, examples according to the above-described embodiment of the present invention will be described.
However, the examples do not limit the scope of the present invention. In particular, while the wavelengths of beam B in the examples are 1064 nm and 355 nm, the wavelength of beam B in the present invention is not limited to these.
Furthermore, depending on how the present invention is interpreted, an Example may be essentially a Comparative Example outside the scope of the present invention, or a Comparative Example may be essentially an Example within the scope of the present invention.

[Example 1: Flat top with hem 1]
<Composition, etc.>
As a first embodiment of the present invention, a beam shaper 1 including an optical multilayer film 8 as a conversion filter from a Gaussian type to a flat-top type (flat-top with a skirt) in the first embodiment was formed.
The various values are as shown in Table 1 below. The physical film thickness of each layer ( _{odd layers: Ta2O5 ,} even layers: _SiO2 ) of the optical multilayer film 8 is as shown in Fig. 5. The physical film thickness of each layer (odd layers: _SiO2 , even _layers : _Ta2O5 ) of the anti-reflection film 10 is as shown in Fig. 6.

<Linear polarization and incident position, etc.>
7 is a schematic diagram of the lens 2 and the optical thin film filter 4 viewed from above the lens 2, in which the beam B is linearly polarized. In FIG. 7, the x-axis is perpendicular to the optical axis L of the lens 2 and corresponds to the direction of linear polarization. The y-axis is perpendicular to the optical axis L of the lens 2 and the x-axis.
7. With the central axis of beam B coinciding with the optical axis L (z-axis), beam B travels from the front of the paper to the back (z-axis + direction) of the paper in Fig. 7. Beam B is refracted by lens 2 toward focal point F and enters optical thin-film filter 4 (optical multilayer film 8) at an angle θ.
The beam B incident on the optical multilayer film 8 in the xz plane P1 is p-polarized light. More specifically, the ratio of the p-polarized light intensity to the total intensity of the beam B is 1, and the ratio of the s-polarized light intensity to the total intensity of the beam B is 0.
On the other hand, the beam B incident on the optical multilayer film 8 in the yz plane P2 becomes s-polarized light. More specifically, the p-polarized light intensity ratio is 0, and the s-polarized light intensity ratio is 1.
On the other hand, the beam B incident on the plane P3, which is obtained by rotating the xz plane by the azimuth angle φ around the z axis (counterclockwise in FIG. 7), has both p-polarized and s-polarized light. More specifically, the radial component of the beam B (proportional to cosφ) is p-polarized light, and the azimuth component (proportional to sinφ) is s-polarized light, with the p-polarized light intensity ratio being (cosφ) ² and the s-polarized light intensity ratio being (sinφ) ² .
From the viewpoint of making the beam B symmetric in intensity around the optical axis L after passing through the optical multilayer film 8, it is preferable that the transmittance characteristics of the optical multilayer film 8 are the same for p-polarized light and s-polarized light. Also, from the viewpoint of maintaining the polarization state before passing through the optical multilayer film 8, it is preferable that the transmittance characteristics of the optical multilayer film 8 are such that the phase difference between p-polarized light and s-polarized light before and after passing through is zero.
When the characteristics of the optical multilayer 8 are caused to differ from the desired state due to its design and/or manufacture, the linearly polarized beam B becomes elliptically polarized upon passing through the optical multilayer 8 .

<Circular polarization and incident position, etc.>
FIG. 8 is a view similar to FIG. 7, but for the case where beam B is circularly polarized.
For circularly polarized light, the ratio of p-polarized to s-polarized components is always 1:1.
Therefore, circularly polarized light is preserved if the optical properties of the optical multilayer film 8 are equivalent for p-polarized light and for s-polarized light, and if the phase difference between p-polarized light and s-polarized light after passing through the optical multilayer film 8 is zero.
When the characteristics of the optical multilayer 8 are caused to deviate from the desired state due to its design and/or manufacture, the circularly polarized beam B becomes elliptically polarized upon passing through the optical multilayer 8 .
It is known that in laser processing, when cutting is performed with a linearly polarized or elliptically polarized beam B, the absorption of light differs depending on the polarization direction of the beam B incident on the workpiece WO, resulting in differences in processing quality such as the processing width and surface roughness depending on the processing direction, and that in order to avoid this, processing can be performed with a non-anisotropic circularly polarized beam B. From this perspective, it is preferable for the optical multilayer film 8 to pass the circularly polarized beam B as it is, and the optical multilayer film 8 of Example 1 is designed in consideration of this perspective.

Here, the ellipticity is shown as an index relating to the extent to which the circularly polarized state of the beam B is maintained while passing through the optical multilayer film 8 .
Fig. 9 is a schematic diagram of ellipticity, and is a graph showing an example of the trajectory of the electric field vector of the beam B (elliptically polarized) after passing through the optical multilayer film 8. In Fig. 9, E _p is the electric field of p-polarized light, and E _s is the electric field of s-polarized light. The center of the ellipse relating to the trajectory of the electric field vector passes through the intersection (origin) of E _p and E _s .
Assume that beam B, which has an electric field of the following formula (6) before passing through the optical multilayer coating 8, has an electric field of the following formula (7) after passing through the optical multilayer coating 8, as shown in Fig. 9. Here, a _p is the amplitude of E _p before passing through the optical multilayer coating 8, a _s is the amplitude of E _s before passing through the optical multilayer coating 8, ω is the frequency, Δ ₀ is a parameter representing the polarization state (linearly polarized light at 0°, and circularly polarized light that is clockwise when viewed from the light receiving side at +90°), T _p is the transmittance of the optical multilayer coating 8 for s-polarized light, T _s is the transmittance of the optical multilayer coating 8 for s-polarized light, and Δ is the transmission phase difference, i.e., the phase difference δ _p - _{δ s} between p-polarized light and s-polarized light.

In other words, the trajectory of the electric field vector of beam B after passing through optical multilayer film 8 oscillates with an amplitude a _{p '} = a _p √T _p in the direction of E _ξ rotated counterclockwise in Figure 9 by the polarization azimuth angle ψ relative to E p, and oscillates with an amplitude a _s ' = a _s √T _s in the direction of E _η rotated counterclockwise in Figure 9 by the polarization azimuth angle ψ relative to E _s .
The ellipticity k is expressed by equations (8) and ( _{9) using (a p ', a s ') or the ellipticity angle χ, which is the angle between the E ξ axis and the line} segment from the origin to (a _p ', a _s ') on the E ξ E η plane.

The ellipticity k is such that 1 indicates right-handed circular polarization, 0 indicates linear polarization, and -1 indicates left-handed circular polarization.
The polarization azimuth angle ψ is expressed by the following equation (10), the E _ξ axis is expressed by the following equation (11), and the E _η axis is expressed by the following equation (12).

The ellipticity k can also be used as an index relating to the degree to which linearly polarized light is passed through the optical multilayer film 8 while maintaining its linearly polarized state.
In other words, while linearly polarized light has an ellipticity k = 0, if the linear polarization is perfectly maintained even after conversion, the ellipticity k will remain 0, and if the light becomes elliptically polarized after conversion, the greater the ellipticity k, the farther it will deviate from linearly polarized light.

<<Transformation of linearly polarized light, etc.>>
FIG. 10 is a graph showing the spectral transmittance distribution of the optical multilayer film 8 of Example 1 when the beam B is incident at an angle θ=0° at each wavelength in a wavelength range including 1064 nm.
The optical multilayer film 8 of the first embodiment is designed for a beam B having a wavelength of 1064 nm (basic wavelength of Nd:YAG (Neodymium:Yttrium Aluminum Garnet) laser). In FIG. 10, the transmittance at a wavelength of 1064 nm is 50%, and at a wavelength of 1064±10 nm, the transmittance increases monotonically from 5% to about 95%, and at a wavelength of 1064+10 nm or more, the transmittance is close to 100% (95% or more) and continues up to a wavelength of about 1100 nm. The transmittance characteristic shifts to the short wavelength side with an increase in the incident angle θ. Then, the transmittance at a wavelength of 1064 nm when shifted to the short wavelength side increases with an increase in the shift amount (angle θ), and is close to 100% at a predetermined angle θ or more.

FIG. 11 is a graph showing the target transmittance value T(θ), the transmittance T _p for p-polarized light, the transmittance T _s for s-polarized light, and the phase difference Δ (vertical axis) when a beam B having a wavelength of 1064 nm is incident on the optical multilayer film 8 of Example 1 at an angle θ (horizontal axis).
In designing the optical multilayer film 8, a target value T(θ) of the transmittance which changes with the angle θ is set so that the transmittance is 50% at an incident angle θ=0°, and the transmittance increases monotonically so as to cancel out the top curve of the Gaussian-type cross-sectional intensity distribution up to an angle θ of just over 9°, and beyond that angle the transmittance is maintained at 100%.
The actual transmittance T _r (θ) of the optical multilayer film 8 is sufficiently close to the target value T(θ) for both the transmittance _Tp for p-polarized light and the transmittance _Ts for s-polarized light.
Strictly speaking, when the angle of incidence θ is about 3° or more, a deviation occurs between the transmittances T _p and T _s and the phase difference Δ also moves away from 0°, so that the transmittance becomes dependent on the polarization.

Fig. 12 is a graph showing the relationship between spatial coordinates (horizontal axis) and the target transmittance value T(θ), transmittance _Tp for p-polarized light, transmittance _Ts for s-polarized light, and incidence angle θ (vertical axis) for beam B with a wavelength of 1064 nm for the optical multilayer coating 8 of Example 1. Fig. 12 shows beam B immediately after passing through the optical multilayer coating 8. The spatial distribution of beam B is similarly reduced around the optical axis L due to convergence until it reaches the workpiece WO. Such matters immediately after passing and matters of reduction apply similarly hereinafter as appropriate.
The spatial coordinates are expressed as a set of a point at a distance d in a certain radial direction perpendicular to the optical axis L and a point at a distance d in the opposite direction, which is a negative value. For example, on a line perpendicular to the optical axis L in a plane of an azimuth angle φ, a point at a distance d from one optical axis L is represented as a spatial coordinate +d, and a point at a distance d from the other optical axis L is represented as a spatial coordinate -d.
The target value T(θ) of the transmittance of the optical multilayer film 8 increases monotonically with respect to the absolute value of the distance d in a region where the spatial coordinates are within about ±5 mm, that is, in a circular region of about 5 mm radius centered on the optical axis L, in a state symmetrical with the Gaussian type about the horizontal axis. In contrast, the transmittance T _p for p-polarized light and the transmittance T _s for s-polarized light are sufficiently close to each other.

13A, 13B, and 13C are graphs showing the cross-sectional intensity distributions (distributions of relative intensity, with the maximum intensity before conversion being set to 1) and the ellipticity distribution before and after conversion and for the target value, respectively, of linearly polarized beam B in a plane whose azimuth angles φ are 0°, 45°, and 90°, respectively, versus spatial coordinates.
The target value of the cross-sectional intensity distribution is the cross-sectional intensity distribution of the beam B that has passed through the optical multilayer film 8 when the transmittance is the target value T(θ).
The cross-sectional intensity distribution of the optical multilayer film 8 can generally match or closely follow the target value of the cross-sectional intensity distribution at any azimuth angle φ.
Strictly speaking, in the optical multilayer film 8, the transmittance characteristics for s-polarized light and p-polarized light differ depending on the azimuth angle φ, so the cross-sectional intensity distribution of the beam B differs depending on the azimuth angle φ.
The ellipticity k after passing through the optical multilayer film 8 is always 0 when the azimuth angle φ is 0° or 90°, regardless of the spatial coordinates. However, when the azimuth angle φ is any other value, the ellipticity k increases with increasing distance from the optical axis L.

FIG. 14 is a schematic diagram in which a predetermined axis and point in polar coordinates (d, φ) are superimposed on a cross-sectional view of the beam B as seen in the direction in which the beam B travels.
FIG. 15(A) is a graph showing the trajectory of the electric field vector of linearly polarized beam B at point (0,0) shown in FIG. 14 before and after conversion by the optical multilayer film 8 of Example 1, and FIGS. 15(B) to (F) are graphs showing the trajectory of the electric field vector of linearly polarized beam B at points (2,0), (2,22.5), (2,45), (2,67.5), and (2,90), respectively, before and after conversion by the optical multilayer film 8 of Example 1.
16A to 16E are graphs showing the trajectories of the electric field vector of linearly polarized beam B at points (4,0), (4,22.5), (4,45), (4,67.5), and (4,90), respectively, before and after conversion by the optical multilayer film 8 of Example 1.
17A to 17E are graphs showing the trajectories of the electric field vector of linearly polarized beam B at points (10,0), (10,22.5), (10,45), (10,67.5), and (10,90), respectively, before and after conversion by the optical multilayer film 8 of Example 1.

15A, the portion of the linearly polarized beam B passing through (0,0), i.e., the center of the lens 2, is perpendicularly incident on the optical multilayer film 8. Therefore, the polarization of that portion is irrelevant, and the ellipticity k of that portion is 0 before and after the transformation.
15 to 17, for any distance d, the ellipticity k after conversion is maximum at an azimuth angle φ of 45°. Also, for any azimuth angle φ except for 0° and 90°, the ellipticity k becomes large at a distance d of 4 relative to a distance d of 2 (2.0 mm from the optical axis L).
The ellipticity k after passing through the optical multilayer film 8 is also 0.074 at the point (4, 45) where it is maximum in the central portion (effective cross-sectional area) excluding the skirt portion (d = 10 mm) of the cross-sectional intensity distribution of beam B in Figures 15 to 17. In other words, the change in the maximum ellipticity k after conversion (k = 0.074) from before conversion (k = 0) is 0.074, and the polarization state of the linearly polarized beam B is sufficiently maintained before and after conversion, particularly in the central portion.

<Conversion of circularly polarized light, etc.>
18A-18C are graphs similar to FIGS. 13A-13C, showing the conversion of circularly polarized beam B according to Example 1. FIG.
The cross-sectional intensity distribution of the optical multilayer film 8 can generally match or closely follow the target value of the cross-sectional intensity distribution for circularly polarized light at any azimuth angle φ.
Strictly speaking, in the optical multilayer film 8, for circularly polarized light, neither the cross-sectional intensity nor the ellipticity has directional dependence in the direction of the azimuth angle φ. On the other hand, in the direction of the distance d, there is a difference for s-polarized light and a difference for p-polarized light, and both the cross-sectional intensity and the ellipticity have directional dependence.
The ellipticity k after passing through the optical multilayer film 8 is always 1 (circularly polarized) at spatial coordinate=0 (on the optical axis L) regardless of the azimuth angle φ, but decreases as the distance from the optical axis L increases.

19 to 21 are graphs similar to those of FIGS. 15 to 17 for the conversion of circularly polarized beam B according to Example 1. In FIG.
19 to 21, if the distance d is constant, the ellipticity k after passing through the optical multilayer coating 8 is constant at any azimuth angle φ. Moreover, the ellipticity k is 1 on the optical axis L, and decreases as the distance d increases.
The ellipticity k is 0.852 at d = 4.0 mm, which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 19 to 21, and the maximum change in ellipticity k after conversion (k = 0.852) from before conversion (k = 1) is 1 - 0.852 = 0.148, and the polarization state of the circularly polarized beam B is sufficiently maintained before and after conversion, especially in the central portion.
Furthermore, various simulations have shown that it is preferable for the change in ellipticity k (change in ellipticity) to be 0.5 or less, regardless of the polarization state, such as linear polarization or circular polarization, since this makes it difficult for the change in the cross-sectional intensity distribution of the beam B to have an adverse effect on the workpiece WO, etc.

[Example 2: Flat top with hem 2]
<Composition, etc.>
As a second embodiment of the present invention, a beam shaper 1 including an optical multilayer film 8 as a conversion filter from a Gaussian type to a flat-top type in the first embodiment was formed.
The various values are as shown in Table 2 below.
The physical thickness of each layer ( _{odd layers: Ta2O5 ,} even layers: _SiO2 ) of the optical multilayer film 8 is as shown in Fig. 22. The number of layers of the optical multilayer film 8 is the same in Examples 1 and 2, but the physical thickness of each layer in Example 2 is generally greater than that in Example 1.
The anti-reflection film 10 is the same as that in the first embodiment.

<<Transformation of linearly polarized light, etc.>>
Fig. 23 is a view similar to Fig. 10 according to the second embodiment. Fig. 24 is a view similar to Fig. 11 according to the second embodiment. Fig. 25 is a view similar to Fig. 12 according to the second embodiment.
The optical multilayer film 8 of the second embodiment is designed for a beam B having a wavelength of 1064 nm (fundamental wavelength of the Nd:YAG laser).
The transmittance characteristics of the optical multilayer film 8 of Example 2 are generally similar to those of Example 1, and furthermore, the difference between the transmittance _Tp for p-polarized light and the transmittance _Ts for s-polarized light is smaller across various angles θ and spatial coordinates than in Example 1. In particular, in a region of incidence angles θ≦10° corresponding to the central portion (flat portion) of the flat-top cross-sectional intensity distribution, the phase difference Δ is almost 0, and transmittance characteristics that preserve the polarization state before and after conversion are ensured.
Moreover, in the wavelength region from about 1064+10 nm to about 1100 nm, the transmittance is closer to 100% than in the first embodiment.

FIG. 26 is a view similar to FIG. 13 relating to Example 2 of the present invention (linearly polarized light).
27 to 29 are similar to FIGS. 15 to 17 and relate to Example 2 (linearly polarized light) of the present invention.
Since the difference in transmittance characteristics between s-polarized light and p-polarized light in the optical multilayer coating 8 of Example 2 is smaller than the difference in the optical multilayer coating 8 of Example 1, the cross-sectional intensity of beam B passing through the optical multilayer coating 8 of Example 2 becomes even more isotropic than the cross-sectional intensity of Example 1.
In addition, since the phase difference Δ in the second embodiment is smaller than the phase difference Δ in the first embodiment, the change in the ellipticity k in the second embodiment is smaller than the change in the first embodiment.
In other words, the ellipticity k is a maximum of 0.005 at d = 4.0 mm, which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 27 to 29, and the maximum change in ellipticity k after conversion from before conversion is 0.005, and the polarization state of the linearly polarized beam B, particularly in the central portion, is maintained with extremely high precision before and after conversion.

<Conversion of circularly polarized light, etc.>
30 to 33 are similar to FIGS. 18 to 21 and relate to Example 2 (circularly polarized light).
Even in the case of circularly polarized light, the phase difference Δ in the second embodiment is smaller than the phase difference Δ in the first embodiment, so that the change in ellipticity k in the second embodiment is smaller than that in the first embodiment.
That is, the ellipticity k is 0.989 at d = 4.0 mm, which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 31 to 33, and the maximum change in ellipticity k after conversion from before conversion is 0.011, and the polarization state of the circularly polarized beam B, especially in the central portion, is maintained with extremely high precision before and after conversion.

[Example 3: Flat top hem cut type]
<Composition, etc.>
As a third embodiment of the present invention, a beam shaper similar to the beam shaper 1 including an optical multilayer film 8 as a conversion filter from a Gaussian type to a flat-top type in the first embodiment is formed. Here, in the third embodiment, a Gaussian type is converted to a flat-top truncated type. The flat-top truncated type is a type in which the cross-sectional intensity distribution of the central part in the flat-top type is left and the cross-sectional intensity distribution of the skirt part is set to zero (including a type approaching zero), in which the intensity is constant within the full width 2√(2ln2)σ around the optical axis L (central part), and the intensity is zero outside the full width 2√(2ln2)σ (skirt part). The flat-top truncated type is a type of flat-top type. That is, the flat-top type includes a flat-top with skirt type and a flat-top with skirt type.
The various values are as shown in Table 3 below.
The physical thickness of each layer (odd-numbered layers: Ta ₂ O ₅ , even-numbered layers: SiO ₂ ) of the optical multilayer film 8 is as shown in Fig. 34. The number of layers of the optical multilayer film 8 is greater than those of the first and second embodiments.
The anti-reflection film 10 is the same as that in the first embodiment.

<<Transformation of linearly polarized light, etc.>>
Fig. 35 is a view similar to Fig. 10 according to the third embodiment. Fig. 36 is a view similar to Fig. 11 according to the third embodiment. Fig. 37 is a view similar to Fig. 12 according to the third embodiment.
The optical multilayer film 8 of the third embodiment is designed for a beam B having a wavelength of 1064 nm (fundamental wavelength of the Nd:YAG laser).
The transmittance characteristics of the optical multilayer film 8 of Example 3 are similar to those of Example 2 up to a wavelength of approximately 1070 nm, at which point the transmittance drops sharply from near 100% to 0%, and further on the longer wavelength side, the transmittance is maintained at 0%.

FIG. 38 is a view similar to FIG. 13 relating to Example 3 of the present invention (linearly polarized light).
The optical multilayer coating 8 of Example 3 sufficiently follows the target value of the cross-sectional intensity distribution of beam B at any azimuth angle φ. Strictly speaking, it is generally difficult to configure a filter in which the transmittance drops sharply from nearly 100% to 0% within an extremely narrow wavelength range, and the cross-sectional intensity distribution of beam B after conversion has some distortion with respect to the portion of the transmittance distribution close to the vertical at the target value of the cross-sectional intensity distribution.
39 to 41 are similar to FIGS. 15 to 17 and relate to Example 3 (linearly polarized light) of the present invention.
Since the difference in transmittance characteristics between s-polarized light and p-polarized light in the optical multilayer film 8 of Example 3 is sufficiently small, the cross-sectional intensity distribution of the beam B that has passed through the optical multilayer film 8 of Example 3 is sufficiently isotropic.
Moreover, since the phase difference Δ in Example 3 is sufficiently small, the change in ellipticity k in Example 3 is sufficiently small. That is, the ellipticity k is a maximum of 0.008 at d=2.0 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 39 to 41, the maximum change in ellipticity k after conversion from before conversion is 0.008, and the polarization state of linearly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.

<Conversion of circularly polarized light, etc.>
42 to 45 are similar to FIGS. 18 to 21 and relate to Example 3 (circularly polarized light).
Even in the case of circularly polarized light, the phase difference Δ in Example 3 is sufficiently small, and therefore the change in ellipticity k in Example 3 is sufficiently small. That is, the ellipticity k is 0.985 at d=2.0 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 43 to 45, and the maximum change in ellipticity k after conversion from before conversion is 0.015, and the polarization state of circularly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.
Moreover, the electric field vector trajectory of the beam B after conversion at a distance d=10 mm (FIG. 45) is almost zero, and the effect of the truncation in the flat top truncated type appears.

[Example 4: Flat top with hem 3]
<Composition, etc.>
As a fourth embodiment of the present invention, a beam shaper 1 including an optical multilayer film 8 as a conversion filter from a Gaussian type to a flat-top type in the first embodiment was formed.
The various values are as shown in Table 4 below.
The physical film thickness of each layer (odd-numbered layers: HfO ₂ , even-numbered layers: SiO ₂ ) of the optical multilayer film 8 is as shown in FIG.
The physical film thickness of each layer of the anti-reflection coating 10 (odd-numbered layers: SiO ₂ , even-numbered layers: HfO ₂ ) is as shown in FIG.
The optical multilayer film 8 of Example 4 is designed for a beam B (third harmonic of Nd:YAG laser) having a wavelength of 355 nm. The FWHM is narrower than those of Examples 1 to 3, the outer diameter and focal length f of the lens 2 are smaller than those of Examples 1 to 3, and θ _max is larger than those of Examples 1 to 3.

<<Transformation of linearly polarized light, etc.>>
48 to 50 are similar to FIGS. 10 to 12 according to the fourth embodiment.
In Fig. 48, the transmittance of the optical multilayer film 8 of Example 4 at a wavelength of 355 nm is 50%, and at a wavelength of 355 ± 5 nm, the transmittance increases monotonically from 10% to about 98%, and at a wavelength of 355 + 5 nm or more, the transmittance is close to 100% (96% or more) and continues up to a wavelength of about 373 nm. The transmittance characteristic shifts to the short wavelength side as the incident angle θ increases. When shifted to the short wavelength side, the transmittance at a wavelength of 355 nm increases with an increase in the shift amount (angle θ) and approaches 100% at a predetermined angle θ or more.

FIG. 51 is a view similar to FIG. 13 relating to Example 4 of the present invention (linearly polarized light).
The optical multilayer film 8 of Example 4 sufficiently follows the target value of the cross-sectional intensity distribution of the beam B (up to about θmax=31.1°) at any azimuth angle φ.
52 to 54 are similar to Figs. 15 to 17 for Example 4 (linearly polarized light) of the present invention. However, instead of the points (2,0), (2,22.5), (2,45), (2,67.5), and (2,90) corresponding to d=2, the points (0.5,0), (0.5,22.5), (0.5,45), (0.5,67.5), and (0.5,90) corresponding to d=0.5 are shown, and similarly, instead of the points corresponding to d=4, the points corresponding to d=1.0 are shown, and instead of the points corresponding to d=10, the points corresponding to d=2.5 are shown. This is also true for the circularly polarized light of Example 4 described later.
Since the difference in transmittance characteristics between s-polarized light and p-polarized light in the optical multilayer film 8 of Example 4 is sufficiently small, the cross-sectional intensity distribution of the beam B that has passed through the optical multilayer film 8 of Example 4 is sufficiently isotropic.
Furthermore, since the phase difference Δ in Example 4 is sufficiently small, the change in ellipticity k in Example 4 is sufficiently small. That is, the ellipticity k is a maximum of 0.011 at d=1.0 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 52 to 54, the maximum change in ellipticity k after conversion from before conversion is 0.011, and the polarization state of linearly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.

<Conversion of circularly polarized light, etc.>
55 to 58 are similar to FIGS. 18 to 21 and relate to Example 4 (circular polarization).
Even in the case of circularly polarized light, the phase difference Δ in Example 4 is sufficiently small, and therefore the change in ellipticity k in Example 4 is sufficiently small. That is, the ellipticity k is 0.978 at d=1.0 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 56 to 58, and the maximum change in ellipticity k after conversion from before conversion is 0.022, and the polarization state of circularly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.

[Example 5: Donut type]
<Composition, etc.>
As a fifth embodiment of the present invention, a beam shaper similar to the beam shaper 1 in the first embodiment is formed. The optical multilayer film 8 of the fifth embodiment converts a flat-top cut-bottom type into a doughnut type. The doughnut type has a central intensity reduction portion where the intensity drops within a portion where the intensity is flat other than 0 in the flat-top cut-bottom type. Here, the intensity is 0 in a cylindrical portion within a total width of about 2 mm (about ±1 mm from the optical axis L) centered on the optical axis L (hole portion), and outside of that, the intensity is constant within the total width of the outer diameter 2√(2ln2)σ centered on the optical axis L (central portion), and the intensity is 0 outside the total width 2√(2ln2)σ. In the doughnut type, the central portion excluding the hole portion is the effective cross-sectional area. The beam B having a doughnut-shaped cross-sectional intensity distribution is used, for example, when processing a fine protrusion having a shape corresponding to the hole portion. The optical multilayer film 8 may be one that converts a flat-top with a bottom type into a doughnut type, etc.
Various values in Example 5 are as shown in Table 5 below.
Moreover, the physical film thickness of each layer (odd-numbered layers: HfO ₂ , even-numbered layers: SiO ₂ ) of the optical multilayer film 8 is as shown in Fig. 59. The number of layers of the optical multilayer film 8 is greater than that of the fourth embodiment.
The optical multilayer film 8 of the fourth embodiment is designed for a beam B (third harmonic of Nd:YAG laser) having a wavelength of 355 nm, the cross-sectional intensity distribution of which is adjusted to a flat-top truncated type.
The anti-reflection film 10 is the same as that in the fourth embodiment.

<<Transformation of linearly polarized light, etc.>>
60 to 62 are similar to FIGS. 10 to 12 according to the fifth embodiment.
The transmittance characteristics of the optical multilayer film 8 of Example 5 are such that the transmittance is 0% or close to 0% in the short wavelength region up to a wavelength of about 355 nm, the transmittance rapidly increases to nearly 100% (about 95%) in the narrow wavelength region from about 355 nm to +2 nm, and the transmittance is maintained close to 100% on the longer wavelength side of a wavelength of about 355 + 2 nm.

FIG. 63 is a view similar to FIG. 13 relating to Example 5 of the present invention (linearly polarized light).
The optical multilayer coating 8 of Example 5 sufficiently follows the target value of the cross-sectional intensity distribution of beam B at any azimuth angle φ. Strictly speaking, it is generally difficult to configure a filter that rapidly increases the transmittance from near 0% to 100% within an extremely narrow wavelength range, and the cross-sectional intensity distribution of beam B after conversion has some distortion with respect to the portion of the transmittance distribution that is close to vertical at the target value of the cross-sectional intensity distribution.
Figures 64 and 65 are similar to Figures 52 and 53 for Example 5 (linearly polarized light) of the present invention. In Example 5, when the distance d = 3.0, there was no electric field before and after conversion at any azimuth angle φ, so the diagram for d = 3.0 (corresponding to Figure 54) is omitted in Example 5. This is also true for the case of circularly polarized light in Example 5.
In the optical multilayer coating 8 of Example 5, at each point at a distance d=0.5 close to the optical axis L (FIG. 64), the trajectory of the electric field vector before the conversion is reduced after the conversion. Such reduction is a manifestation of the formation of a doughnut-shaped hole portion. On the other hand, in the optical multilayer coating 8 of Example 5, at each point at a distance d=1.5 slightly away from the optical axis L (FIG. 65), the trajectory of the electric field vector before the conversion is relatively maintained even after the conversion. Such maintenance is a manifestation of the formation of a doughnut-shaped effective cross-sectional area portion.
The difference in transmittance characteristics between s-polarized light and p-polarized light in the optical multilayer coating 8 of Example 5 is sufficiently small, particularly in the region where the spatial coordinates are within ±3 mm, so that the doughnut-shaped cross-sectional intensity distribution of beam B that has passed through the optical multilayer coating 8 of Example 5 is sufficiently isotropic.
Furthermore, since the phase difference Δ in Example 5 is sufficiently small, the change in ellipticity k in Example 5 is sufficiently small. That is, the ellipticity k is a maximum of 0.021 at d=1.5 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 64 and 65, and the maximum change in ellipticity k after conversion from before conversion is 0.021, and the polarization state of linearly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.

<Conversion of circularly polarized light, etc.>
FIG. 66 is a view similar to FIG. 18 relating to Example 5 (circularly polarized light).
67-68 are similar to FIGS. 56-57 and relate to Example 5 (circularly polarized light).
In the optical multilayer film 8 of Example 5, even in the case of circularly polarized light, at each point at a distance d = 0.5 close to the optical axis L (Figure 67), the trajectory of the electric field vector before conversion is contracted after conversion, and at each point at a distance d = 1.5 slightly away from the optical axis L (Figure 68), the trajectory of the electric field vector before conversion is maintained even after conversion.
Furthermore, even in the case of circularly polarized light, the phase difference Δ in Example 5 is sufficiently small, and therefore the change in ellipticity k in Example 5 is sufficiently small. That is, the ellipticity k is 0.958 at d=1.5 mm which belongs to the central portion (effective cross-sectional area) of the cross-sectional intensity distribution of beam B in Figures 67 to 68, and the maximum change in ellipticity k after conversion from before conversion is 0.042, and the polarization state of circularly polarized beam B is maintained with extremely high precision before and after conversion, particularly in the central portion.

In the fifth embodiment, the cross-sectional intensity distribution of the beam B before it is incident on the optical multilayer film 8 is a flat-top type, and the cross-sectional intensity distribution of the beam B converted by the optical multilayer film 8 is a doughnut type.
Therefore, a doughnut-shaped beam B capable of processing a minute protrusion can be realized by the optical thin film filter 4 which is easy to manufacture and has a long life.

1, 101, 201, 301...beam shaper, 2, 102, 112, 202, 212, 222, 312...lens, 4...optical thin film filter, 6...substrate, 8...optical multilayer film, 120, 230...case, 124, 334...pinhole plate, B...beam (light ray), PH...pinhole, R...surface (of substrate 6), R'...surface (of lens 2), WO...workpiece, θ...angle (incident angle), θ _max ...maximum value (of angle θ).

Claims (8)

A substrate;
an optical multilayer film formed on a surface of the substrate;
Equipped with
the optical multilayer film has an incident angle-dependent transmittance, which is a transmittance according to an incident angle of a light beam at a wavelength of the light beam incident thereon, due to interference, and converts a cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance ;
An ellipticity change amount, which is an amount of change between the ellipticity of the electric field of the light beam before it is incident on the optical multilayer film and the ellipticity of the electric field of the light beam whose cross-sectional intensity distribution has been converted by the optical multilayer film, is 0.5 or less.
1. An optical thin film filter comprising: A substrate;
an optical multilayer film formed on a surface of the substrate;
Equipped with
the optical multilayer film has an incident angle-dependent transmittance, which is a transmittance according to an incident angle of a light beam at a wavelength of the light beam incident thereon, due to interference, and converts a cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance;
a cross-sectional intensity distribution of the light beam before it is incident on the optical multilayer film is Gaussian type;
An optical thin film filter, wherein the cross-sectional intensity distribution of the light beam converted by the optical multilayer film is a flat-top type. A substrate;
an optical multilayer film formed on a surface of the substrate;
Equipped with
the optical multilayer film has an incident angle-dependent transmittance, which is a transmittance according to an incident angle of a light beam at a wavelength of the light beam incident thereon, due to interference, and converts a cross-sectional intensity distribution of the light beam refracted and incident on the optical multilayer film by the incident angle-dependent transmittance;
a cross-sectional intensity distribution of the light beam before it is incident on the optical multilayer film is a flat-top type;
An optical thin film filter , characterized in that the cross-sectional intensity distribution of the light beam converted by the optical multilayer film is doughnut-shaped. An optical thin film filter according to any one of claims 1 to 3 ;
One or more lenses;
Equipped with
A beam shaper, characterized in that at least one of the lenses refracts the light beam and makes it incident on the optical thin film filter. 5. The beam shaper of claim 4 , wherein at least one of the optical thin film filter and the one or more lenses is housed in a case. a pinhole plate having a pinhole is provided upstream of the optical thin film filter,
6. A beam shaper according to claim 4 or claim 5 , wherein at least one of the lenses focuses the light beam at the pinhole. 7. The beam shaper according to claim 4 , wherein some or all of the plurality of lenses are arranged upstream of the light beam from the optical thin film filter and expand the diameter of the light beam. 8. The beam shaper according to claim 4 , wherein a single lens on which the optical multilayer film is formed is disposed in place of the optical thin film filter and one of the lenses.

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