JPH10339891A - Wavelength converting device and ultraviolet laser device using same - Google Patents

Abstract

(57) Abstract: A wavelength conversion device having a high wavelength conversion efficiency and a compact configuration without requiring high peak output laser light as a fundamental wave. A second nonlinear optical crystal (21) of the frequency omega ₁ of the laser beam at the beam center position and frequency 2 [omega ₂
Beam center position adjusting means (24, 25) for making the beam center position of the (4ω ₁ ) laser beam substantially coincide with the common optical element, and a second nonlinear optical crystal (21)
Beam shape and frequency 2 at frequency ω ₁
Beam shape matching means (2) for matching the beam shape of the laser light of ω ₂ (4ω ₁ ) with a common optical element.
6).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength conversion device and an ultraviolet laser device using the wavelength conversion device, and more particularly to a near-infrared light, a visible light and an ultraviolet light using a nonlinear optical crystal having birefringence. The present invention relates to an apparatus for converting a wavelength into ultraviolet light having a short wavelength.

[0002]

2. Description of the Related Art In the field of micromachining such as an exposure machine used in a semiconductor manufacturing process, for example,
d: YAG (Yttrium Aluminum Garne doped with Nd
t) as a laser medium (hereinafter simply referred to as “N
d: YAG laser ”) (1064n).
Attention has been paid to the application of an ultraviolet light source using the fifth harmonic (213 nm) obtained by wavelength conversion of m). In general, Nd:
In a conventional wavelength converter that converts the wavelength of a fundamental wave of a YAG laser into a fifth harmonic, a nonlinear optical crystal LBO (LiB ₃ O ₅ ) or the like is used as a second harmonic generation element in a second harmonic generation unit. , A second harmonic is generated from the fundamental wave. Then 4
Using a nonlinear optical crystal BBO (β-BaB ₂ O ₄ ) as a second harmonic generation element in the harmonic generation section,
Generates harmonics. Finally, the fifth harmonic is generated from the fundamental wave and the fourth harmonic by using the nonlinear optical crystal BBO as the sum frequency generating element in the fifth harmonic generation unit.

FIG. 9 is a diagram showing a state of generation of a fourth harmonic in a nonlinear optical crystal BBO constituting a fourth harmonic generation unit of a conventional wavelength converter. FIG.
(B) shows the beam position and beam shape of each laser beam at the emission end of the BBO crystal. The fourth harmonic generation portion of the wavelength conversion device shown in FIG. 9, Nd: fundamental wave of YAG laser and (i.e. laser beam of a frequency omega ₁₎ and second harmonic (i.e. laser beam of frequency 2 [omega ₁₎ is along the same optical path (Coaxially) and enters the BBO crystal 90 having strong birefringence. And the BBO crystal 90
In a extraordinary light from the second harmonic of the incident quadruple wave (i.e. laser beam of frequency 4ω ₁₎ is generated as ordinary light.

[0004] That is, as shown in FIG. 9A, the fourth harmonic, which is extraordinary light, has a predetermined walk-off angle (Walk) in a predetermined direction from each generation point on the beam center axis of the second harmonic, which is ordinary light. The light propagates through the BBO crystal 90 with an off angle. A phenomenon in which extraordinary light propagates through the nonlinear optical crystal at a predetermined angle in a predetermined direction from each generation point on the beam central axis of the ordinary light is called “walk off”.
As a result, as shown in FIG. 9B, at the exit end of the BBO crystal 90, the beam shape of the fourth harmonic becomes an elongated beam extending in the walk-off direction, and the beam center of the fourth harmonic and the second harmonic. Does not coincide with the beam center. The fundamental wave incident as extraordinary light is also affected by birefringence in the BBO crystal 90, and its beam center axis is shifted from the beam center axis of the second harmonic in the direction of the birefringence angle, but its beam shape is unchanged. .

[0005]

In the conventional wavelength converter configured as described above, B which constitutes the fourth harmonic generator is used.
Due to the effect of the walk-off in the BO crystal, not only does the beam overlap of the second harmonic and the fourth harmonic decrease, so that the efficiency of generating the fourth harmonic decreases, but also the BBO crystal constituting the subsequent fifth harmonic generating section. In this case, the beam overlap between the fundamental wave and the fourth harmonic is reduced, and the efficiency of fifth harmonic generation is reduced. That is,
The wavelength conversion efficiency of the wavelength conversion device is reduced due to the walk-off of the fourth harmonic in the fourth harmonic generation unit.

In order to improve the wavelength conversion efficiency by compensating the influence of the walk-off of the fourth harmonic in the above-mentioned fourth harmonic generation part, a pair of BBO crystals whose crystal axes are inverted are moved along the traveling direction of light. A method of arranging them in series to constitute a fourth harmonic wave generating unit is conceivable. FIG. 10 shows a conventional wavelength conversion device in which a pair of BBO crystals whose crystal axes are inverted are arranged in series.
It is a figure which shows the mode that the harmonic generation part was comprised, (a) shows a mode that each laser beam propagates through a pair of BBO crystal,
(B) shows the beam position and beam shape of each laser beam at the exit end of the BBO crystal in the latter stage, respectively.

[0007] As shown in FIG.
In the crystal 91, similarly to the BBO crystal 90 in FIG.
The fourth harmonic (frequency 4ω ₁ ) propagates from each generation point on the beam center axis of the second harmonic (frequency 2ω ₁ ) downward at a predetermined walk-off angle in the drawing. On the other hand, in the BBO crystal 92 at the subsequent stage, the fourth harmonic propagates from each generation point on the beam center axis of the second harmonic upward at a predetermined walk-off angle in the drawing. As a result, the beam overlap between the second harmonic and the fourth harmonic in the fourth harmonic generator is improved, and the efficiency of fourth harmonic generation is improved. However, as shown in FIG. 10B, at the exit end of the BBO crystal 92 at the subsequent stage, the beam shape of the fourth harmonic becomes an elongated beam extending in a predetermined direction, and the beam center of the fourth harmonic and the beam center of the second harmonic. It does not coincide with the beam center. As a result, the beam overlap between the fundamental wave (frequency ω ₁ ) and the fourth harmonic wave in the BBO crystal 93 constituting the fifth harmonic wave generation unit does not improve, and the efficiency of the fifth harmonic wave generation does not improve.

The following two methods can be considered to improve the efficiency of generating the fifth harmonic by improving the beam overlap between the fundamental wave and the fourth harmonic in the fifth harmonic generator. In the first method, a large beam shape is used so that the spread of the beam shape of the fourth harmonic due to the influence of the walk-off does not matter. That is, the beam shapes of the fundamental wave and the second harmonic wave coaxially incident on the fourth harmonic wave generation unit, that is, the beam shapes of the fundamental wave incident on the second harmonic wave generation unit (not shown) are set large. In the second method, the optical path of the fundamental wave and the optical path of the fourth harmonic wave incident on the fifth harmonic wave generation unit are spatially separated, and the fifth harmonic wave generation unit is separated via the optical systems respectively arranged in each optical path. The beam overlap between the fundamental wave and the fourth harmonic in the nonlinear optical crystal to be constituted is improved.

However, according to the first method, the beam diameter of the fundamental wave incident on the fifth harmonic wave generator cannot be set small. For this reason, the fundamental wave cannot secure a high power density necessary for obtaining good conversion efficiency in the nonlinear optical crystal of the fifth harmonic generation part. In other words, in order to obtain good conversion efficiency in the fifth harmonic generation unit,
A very high peak power laser is required. On the other hand, according to the second method, it is not only complicated to adjust the overlap of the beam of the fundamental wave and the beam of the fourth harmonic through two independent optical systems, but also the second harmonic generator and the fourth harmonic. Generator and 5
This makes it impossible to adopt a compact configuration in which the harmonic generation unit is arranged in series along a straight line.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides a wavelength conversion device having a high wavelength conversion efficiency and a compact configuration without requiring high peak output laser light as a fundamental wave. The purpose is to provide. It is another object of the present invention to provide an ultraviolet laser device having sufficient output and low coherence as a light source of a semiconductor exposure apparatus, using the wavelength conversion device of the present invention.

[0011]

According to the present invention, there is provided a first nonlinear optical crystal having birefringence, and a frequency ω ₁ incident on the first nonlinear optical crystal. And the laser beam is transmitted without changing its frequency and emitted, and the frequency 2ω ₂ whose beam shape extends in a predetermined direction based on the laser beam of frequency ω ₂ incident as ordinary light on the first nonlinear optical crystal. A second harmonic generating means for generating and emitting the extraordinary light, and a second nonlinear optical crystal having birefringence, wherein the second nonlinear optical crystal is connected to the second nonlinear optical crystal via the first nonlinear optical crystal. The incident laser light of frequency ω ₁ and the frequency 2 incident on the second nonlinear optical crystal via the first nonlinear optical crystal
frequency (ω ₁ + 2ω ₂ ) based on the laser light of ω ₂
Of the sum frequency generation means to generate a laser beam emitted by the second laser beam of the frequency omega ₁ in the nonlinear optical crystal beam center position and the laser beam of frequency 2 [omega ₂ beam center position and the common a beam center position adjusting means for substantially coincident with the optical element, the second the frequency omega ₁ of the laser light beam shaped in a nonlinear optical crystal and said frequency 2 [omega ₂ of the laser light beam shape and a common And a beam shape matching means for performing matching using an optical element.

According to a preferred aspect of the present invention, the beam center position adjusting means is provided in the optical path on the incident side of the second harmonic generating means or between the second harmonic generating means and the sum frequency generating means. Has a plane-parallel plate or a pair of prisms arranged in the optical path. Further, it is preferable that the beam shape matching means has a lens arranged in an optical path between the second harmonic generation means and the sum frequency generation means. In this case, it is more preferable that the lenses have different refractive powers in a plane orthogonal to the optical axis.

According to another aspect of the present invention, a laser unit having a wavelength converter of the present invention and a laser device for supplying a laser beam having a predetermined frequency to the wavelength converter is provided in parallel. Each laser unit is provided with a plurality of laser units, and each laser unit converts the wavelength of the laser light from the laser device into ultraviolet laser light in the wavelength conversion device and emits the laser light. In this case, the laser device is a semiconductor laser-excited solid-state laser device that performs laser oscillation by optically exciting a solid-state laser medium doped with Nd with a semiconductor laser, and the wavelength converter is a semiconductor laser-excited solid-state laser device. It is preferable to convert the wavelength of the near-infrared laser light into an ultraviolet laser light having a fifth harmonic thereof.

[0014]

1A and 1B are diagrams for explaining the operation of a wavelength conversion device according to the present invention, wherein FIG. 1A shows how each laser beam propagates through the device, and FIG. (C) shows the overlap between the fundamental wave and the fourth harmonic in the BBO crystal of the fifth harmonic generation part at the exit end of the wave generation part.

In a specific configuration example of the wavelength converter according to the present invention, a second harmonic generation unit (not shown) can be provided in a stage preceding the second harmonic generation means. The second harmonic generation unit uses a nonlinear optical crystal LBO to generate a second harmonic (frequency 2) from the fundamental wave (frequency ω ₁ ) of the Nd: YAG laser.
ω ₁ ). The second harmonic generation means is a fourth harmonic generation unit, for example, using a pair of nonlinear optical crystals BBO whose crystal axes are inverted, from the second harmonic to the fourth harmonic (frequency 4ω).
₁ ) Generate. In the subsequent stage of the second harmonic generation means, 5
A sum frequency generation unit as a harmonic generation unit is provided.
The fifth harmonic generation unit generates a fifth harmonic (frequency 5ω) from the fundamental wave and the fourth harmonic using, for example, a nonlinear optical crystal BBO.

According to the present invention, in the specific configuration shown in FIG. 1, for example, a beam center position adjusting section comprising a parallel plane plate or a pair of prisms is provided with an optical path between a second harmonic generating section and a fourth harmonic generating section. It is arranged in the optical path between the middle or fourth harmonic generator and the fifth harmonic generator. Then, the beam center position of the fundamental wave and the beam center position of the fourth harmonic in the nonlinear optical crystal BBO of the fifth harmonic generation unit are made substantially coincident by the operation of the beam center position adjustment unit. In addition, a beam shape matching unit composed of, for example, a lens is disposed in the optical path between the fourth harmonic generation unit and the fifth harmonic generation unit. Then, the beam shape of the fundamental wave and the beam shape of the fourth harmonic in the nonlinear optical crystal BBO of the fifth harmonic generation unit are matched by the function of the beam shape matching unit.

Therefore, as shown in FIG. 1C, even if the beam diameter of the fundamental wave is set small, the B
The effect of the walk-off in the BO crystal can be compensated, and a good beam overlap between the fundamental wave and the fourth harmonic can be ensured in the BBO crystal of the fifth harmonic generation part. As described above, the beam center position adjustment unit and the beam shape matching unit use a common optical element for the fundamental wave and the fourth harmonic without using separate optical systems. Therefore,
The beam center position adjustment unit and the beam shape matching unit can be compactly arranged in a straight line together with the second harmonic generation unit, the fourth harmonic generation unit, and the fifth harmonic generation unit. Thus, according to the present invention, it is possible to realize a wavelength converter having a high wavelength conversion efficiency and a compact configuration without requiring a laser beam having a high peak output as a fundamental wave.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 2 is a diagram schematically showing a configuration of the wavelength conversion device according to the first embodiment of the present invention. In FIG. 2, the z-axis is set parallel to the beam center axis of the fundamental wave and the second harmonic wave coaxially incident on the wavelength converter, and the x-axis and the y-axis are set in directions orthogonal to a plane perpendicular to the z-axis. ing. Therefore, (a) shows the configuration of the device along the xz plane, (b) shows the configuration of the device along the yz plane,
(C) shows the beam overlap of the fundamental wave and the fourth harmonic at the entrance end, the center, and the exit end of the BBO crystal of the fifth harmonic generation part, respectively.

The apparatus of the first embodiment has a fourth harmonic wave generator 20.
And a fifth harmonic wave generating section 21 and a second harmonic wave generating section (not shown) arranged before the fourth harmonic wave generating section 20. The second harmonic generation section uses an LBO crystal as a second harmonic generation element to convert a fundamental wave (wavelength 1064 nm: frequency ω ₁ ) supplied from, for example, an Nd: YAG laser to a second harmonic (wavelength 532 nm: frequency 2ω). The second harmonic generation means for generating ₁ ) is constituted. The fourth harmonic generation unit 20 includes a pair of BBO crystals 22 and 23 as a second harmonic generation element.
Is used to constitute second harmonic generation means for generating a second harmonic to a fourth harmonic (wavelength 266 nm: frequency 4ω ₁ ). The pair of BBO crystals 22 and 23 are arranged in series along the central axis of the incident beam (along the z-axis) such that the crystal axes are inverted. The fifth harmonic generation unit 21 constitutes a sum frequency generation unit that generates a fifth harmonic (wavelength 213 nm: frequency 5ω ₁ ) from a fundamental wave and a fourth harmonic using the BBO crystal 21 as a sum frequency generation element. ing. As shown in FIG. 2A, the thickness of each BBO crystal (the length along the central axis of the incident beam) is 10 mm.
It is.

The apparatus of the first embodiment has an optical path on the incident side of the fourth harmonic generator 20 (the second harmonic generator and the fourth harmonic generator 2).
0) and a spherical lens 26 disposed in the optical path between the fourth harmonic generator 20 and the fifth harmonic generator 21. I have. The pair of prisms 24 and 25 are the fourth harmonic wave generator 2
In order to emit the fundamental wave and the fourth harmonic coaxially from 0, 2
This has the function of translating the fundamental wave and the second harmonic wave coaxially incident from the harmonic wave generating unit by different distances in the x direction, and constitutes a beam center position adjusting means as described later. The spherical lens 26 has a function of condensing the fundamental wave and the fourth harmonic coaxially emitted from the fourth harmonic generation unit 20, and constitutes a beam shape matching unit as described later. As shown in FIG. 2A, both the fundamental wave and the second harmonic supplied coaxially from the second harmonic generation unit have a diameter of 2.
It has a circular beam shape of 00 μm.

FIG. 3 is a diagram for explaining the effect of the walk-off in the fourth harmonic wave generator 20 of the first embodiment.
Referring to FIG. 3A, a pair of BBO crystals 22 and 2 whose crystal axes are inverted without the fundamental wave and the second harmonic wave from the second harmonic wave generating unit passing through a pair of prisms 24 and 25 are shown.
3 is coaxially incident on the fourth harmonic wave generating unit 20, and the fundamental wave and the second harmonic wave from the fourth harmonic wave generating unit 20 are converted into a spherical lens 26.
3 shows a state in which the light is incident on the fifth harmonic generation unit 21 without passing through. In this case, as already described with reference to FIG. 10, the fourth harmonic as the extraordinary light is paired with a walk-off angle of 4.9 ° from each generation point on the beam center axis of the second harmonic as the ordinary light. In the BBO crystal. The fundamental wave, which is extraordinary light, propagates through the BBO crystals 22 and 23 at an angle of 3.9 ° due to birefringence, but the directions thereof are opposite to each other between the BBO crystals 22 and 23. The beam center position is the same as the incident beam on the BBO crystal 22, and its beam shape is unchanged.

Therefore, as shown in FIG.
At the exit end of the harmonic generation unit 20 and the entrance end of the fifth harmonic generation unit 21, the beam shape of the fourth harmonic is 900 μm in the x direction affected by the walk-off and 200 μm in the y direction not affected by the walk-off. It has an elongated shape. on the other hand,
The beam shape of the fundamental wave remains in a circular shape of 200 μm without being affected by the walk-off, and the effect of birefringence on the propagation direction of the fundamental wave, that is, the beam center axis direction is canceled by the pair of BBO crystals 22 and 23. . As described above, when the beam center position adjusting means and the beam shape matching means are not interposed in the first embodiment, 4
Due to the effect of the walk-off in the harmonic generation unit 20, 4
At the exit end of the harmonic generation unit 20 and the entrance end of the fifth harmonic generation unit 21, the beam center of the fundamental wave and the beam center of the fourth harmonic are separated by 350 μm in the x direction.

FIG. 4 is a diagram for explaining the operation of the pair of prisms 24 and 25 constituting the beam center position adjusting means in the first embodiment. As shown in FIG. 4, a pair of prisms 24 and 25 are used to output the fundamental wave and the fourth harmonic wave coaxially from the second harmonic wave generation unit 20 so that the fundamental wave and the fourth harmonic wave are coaxially incident from the second harmonic wave generation unit. The second harmonic is translated in the x direction by different distances from each other. That is,
The beam center axis of the fundamental wave and the beam center axis of the second harmonic incident on the fourth harmonic generator 20 are set to 350 μm along the x direction.
By causing the fundamental wave and the fourth harmonic to be emitted coaxially from the fourth harmonic generation unit 20, and thus by 5
This allows the fundamental wave and the fourth harmonic wave to be coaxially incident on the harmonic wave generation unit 21. Thus, a pair of prisms 2
4 and 25 constitute beam center position adjusting means for making the beam center position of the fundamental wave and the beam center position of the fourth harmonic in the BBO crystal of the fifth harmonic generation unit 21 substantially coincide with each other.

Hereinafter, a specific configuration of the pair of prisms 24 and 25 when the optical material SF57 having a relatively large dispersion (chromatic aberration) is used will be described. Note that the optical material SF57 has n with respect to the fundamental wave (wavelength 1064 nm).
It has a refractive index of (ω ₁ ) = 1.81104 and n (2ω ₁ ) = 1.85850 for the second harmonic (wavelength 532 nm).
Having a refractive index of In the pair of prisms 24 and 25, due to the difference in refractive index due to the wavelength, that is, the dispersion of the optical material, the angle between the incident angle and the exit angle to each prism, that is, the deflection angle of the prism is the wavelength of the beam (that is, the frequency ω). Depends on). Due to this difference in declination, the relative positions of the two incident beams can be shifted by a desired amount. In FIG. 4, a pair of prisms 24 and 25 have opposing surfaces 24a and 25a substantially parallel to each other.
It is separated by a distance L along the direction. In this case, assuming that the apex angle of each prism is A, the angle between the incident angle and the exit angle to the prism, that is, the declination angle of the prism is D, and the refractive index of the optical material of the prism is n, the following equation (1) The relationship shown in parentheses is established. Equation (1) is an equation that is approximately established when the apex angle A of the prism is a small angle of 30 ° as described later, and the incidence on the prism is close to normal incidence. D = A (n-1) (1)

Therefore, the beam center position displacement X at a distance L is expressed by the following equation (2). X = D · L = L · A (n−1) (2) That is, the dispersion (dn (ω) / dω) of the optical material SF57 forming the pair of prisms 24 and 25 depends on the wavelength of the incident beam. Beam center displacement X
(Ω) is obtained. Accordingly, the relative position displacement (X (2ω ₁ ) −X (ω) between the fundamental wave (ω ₁ ) and the second harmonic (2ω ₁ )
₁ )) to a required value of 350 μm, the apex angle A
It is only necessary to dispose a pair of prisms having a distance of 30 ° at a distance L of 15 mm. Note that the apex angle A = 3
If an optical material having a larger dispersion than the optical material SF57 is used without changing 0 °, the distance L can be further reduced, and a more compact configuration can be realized.

FIG. 5 is a view for explaining a modification of the first embodiment in which a parallel plane plate is used as the beam center position adjusting means. In FIG. 5, when the refractive index of the parallel flat plate 51 with respect to the beam having the frequency ω is n (ω), the thickness of the parallel flat plate 51 is t, and the incident angle of the beam on the parallel flat plate 51 is I, The displacement X (ω) of the incident beam is represented by the following equation (3).

(Equation 1)

As described above, the displacement X (ω) depending on the wavelength of the incident beam can be obtained by the dispersion (dn (ω) / dω) of the optical material forming the parallel plane plate 51. When forming the parallel plane plate 51 with the above-described optical material SF57,
The relative position displacement (X (2ω ₁ ) −X (ω ₁ )) between the fundamental wave (ω ₁ ) and the second harmonic (2ω ₁ ) is a required value of 350.
In order to make μm, a parallel flat plate having a thickness of t = 36 mm may be arranged so that the incident angle becomes I = 53 °. If an optical material having a larger dispersion than the optical material SF57 is used without changing the incident angle I = 53 °, the thickness t can be further reduced, and a more compact configuration can be realized.

Here, when comparing the case where the parallel plane plate 51 is used as the beam center position adjusting means with the case where the pair of prisms 24 and 25 are used, refraction on four surfaces can be used with the pair of prisms. Whereas
In a plane-parallel plate, only two surfaces can utilize refraction. Therefore, when the same length and the same optical material are used, the amount of beam displacement can be increased by using a pair of prisms as compared with a plane-parallel plate. In other words, when a pair of prisms is used as the beam center position adjusting means rather than a parallel flat plate, the required beam displacement can be obtained with a shorter length, and a more compact configuration can be realized. .

Returning to FIG. 2, the operation of the spherical lens 26 constituting the beam shape matching means in the first embodiment will be described. As shown in FIG. 2, in the first embodiment, the spherical lens 26 is disposed immediately after the fourth harmonic wave generator 20 and at a distance of 42 mm from the incident end face of the BBO crystal of the fifth harmonic wave generator 21. doing. The spherical lens 26 has a focal length of f (ω ₁ ) = 40 mm with respect to a fundamental wave (wavelength 1064 nm), and has a focal length f with respect to a fourth harmonic (wavelength 266 nm).
It has a focal length of (4ω ₁ ) = 36 mm. In the spherical lens 26, the focal position and the divergence angle of each beam are adjusted by utilizing the dispersion of the optical material forming the lens and the difference in the spread angles of the two incident beams (the fundamental wave and the fourth harmonic). The beam shape of the fundamental wave and the beam shape of the fourth harmonic can be matched at the center of the BBO crystal of the fifth harmonic generation unit 21.

In the first embodiment, the case where there is a beam waist of the fundamental wave and the fourth harmonic at the exit end of the fourth harmonic wave generating section 20, therefore, the curvature of the wavefront at the exit end of the fourth harmonic wave generating section 20 is set to 0. By calculating the Gaussian beam propagation using the ABCD matrix,
The beam diameter of each beam is determined. FIG. 2 (a) to (c)
As shown in the figure, the fundamental wave having a diameter of 200 μm at the exit end of the fourth harmonic wave generation unit 20 is approximately 47 m behind the spherical lens 26.
The beam is shaped into a beam shape having a diameter of 300 μm at the position of m, that is, at the center position of the BBO crystal in the fifth harmonic generation unit 21. On the other hand, the fourth harmonic having a beam shape of 900 μm in the x direction and 200 μm in the y direction at the exit end of the fourth harmonic generator 20 is 300 μm in the x direction at the center position of the BBO crystal of the fifth harmonic generator 21 and y It is shaped into an elliptical beam shape of 100 μm in the direction. Thus, the fifth harmonic generation unit 21
Over the entire BBO crystal from the entrance end to the exit end,
Good beam overlap between the fundamental wave and the fourth harmonic can be realized.

As described above, in the first embodiment, the operation of the beam center position adjusting means disposed in the optical path between the second harmonic wave generating section and the fourth harmonic wave generating section 20 causes the fourth harmonic wave generating section to operate. 20
Of the beam center position of the fundamental wave and the beam center position of the fourth harmonic at the exit end of
The center position of the beam of the fundamental wave and the center position of the beam of the fourth harmonic wave in the crystal are substantially matched. Also, by the action of the beam shape matching means disposed in the optical path between the fourth harmonic generation unit 20 and the fifth harmonic generation unit 21, the B of the fifth harmonic generation unit 21
The beam shape of the fundamental wave and the beam shape of the fourth harmonic in the BO crystal are matched. As a result, by the cooperative action of the beam center position adjusting means and the beam shape matching means, the fundamental wave and the fourth harmonic wave of the fifth harmonic wave generating section 21 from the incident end to the exit end of the BBO crystal are entirely formed. Good beam overlap can be realized in between.

As described above, in the first embodiment, even if the beam diameter of the fundamental wave is set to be as small as 200 μm, the influence of the walk-off in the BBO crystal of the fourth harmonic wave generator 20 is compensated for, and the fifth harmonic wave generator Fundamental wave and 4 in 21 BBO crystals
Good beam overlap with the harmonics can be ensured. Further, a pair of prisms 24 and 25 (or a parallel plane plate 51) constituting the beam center position adjusting means and a spherical lens 26 constituting the beam shape matching means are replaced by 2
Harmonic generator, fourth harmonic generator 20, and fifth harmonic generator 21
And can be arranged compactly in a straight line. Thus, according to the first embodiment, it is possible to realize a wavelength converter having a high wavelength conversion efficiency and a compact configuration without requiring a laser beam having a high peak output as a fundamental wave.

FIG. 6 is a diagram schematically showing the configuration of a wavelength converter according to a second embodiment of the present invention. The second embodiment has a configuration similar to that of the first embodiment. However,
In the first embodiment, a spherical lens is used as the beam shape matching means, whereas in the second embodiment, a cylindrical 61 having a positive refractive power in the x direction and a non-refractive power in the y direction and a non-refractive power in the x direction are used. The only difference is that a cylindrical member 62 having a positive refractive power is used in the y direction. Therefore, in FIG. 6, elements having the same functions as those of the first embodiment in FIG. 2 are denoted by the same reference numerals as in FIG.
Hereinafter, the second embodiment will be described by focusing on the differences from the first embodiment.

As shown in FIG. 6, in the second embodiment, the BBO of the fifth harmonic generation unit 21 immediately after the fourth harmonic generation unit 20 is used.
A pair of cylindrical lenses 61 and 62 are arranged at a distance of 42 mm from the incident end face of the crystal. The cylindrical lens 61 has a focal length of fx (ω ₁ ) = 40 mm with respect to the fundamental wave (wavelength 1064 nm) in the x direction, and has fx with respect to the fourth harmonic (wavelength 266 nm).
It has a focal length of (4ω ₁ ) = 36 mm. On the other hand, the cylindrical lens 62 has a focal length of fy (ω ₁ ) = 20 mm with respect to the fundamental wave (wavelength 1064 nm) in the y direction and has fy (ω ₁ ) with respect to the fourth harmonic (wavelength 266 nm).
It has a focal length of (4ω ₁ ) = 18 mm. In the pair of cylindrical lenses 61 and 62, the focal position and the divergence angle of each beam are separately adjusted in the x direction and the y direction, so that the beam shape of the fundamental wave at the center of the BBO crystal of the fifth harmonic generation unit 21 is adjusted. The beam shape of the fourth harmonic can be better matched with the spherical lens.

As shown in FIGS. 6A to 6C, the fundamental wave having a diameter of 200 μm at the exit end of the fourth harmonic wave generating section 20 is located about 47 mm behind the cylindrical lens 62, that is, the fifth harmonic wave generating section 21. The beam is shaped into a beam having a diameter of about 300 μm at the central position of the BBO crystal. On the other hand, at the emission end of the fourth harmonic wave
The fourth harmonic having a beam shape of 200 μm in the y direction at μm is also shaped into a beam shape having a diameter of about 300 μm at the central position of the BBO crystal of the fifth harmonic generation unit 21. Thus, in the second embodiment, the first embodiment is arranged between the fundamental wave and the fourth harmonic in the x direction and the y direction over the entire area from the incident end to the exit end of the BBO crystal of the fifth harmonic generation unit 21. Better beam overlap can be achieved. In the second embodiment, a plane-parallel plate can be used as the beam center position adjusting means as in the modification of the first embodiment.

FIG. 7 is a diagram schematically showing a configuration of a wavelength converter according to a third embodiment of the present invention. The third embodiment has a similar configuration to the first and second embodiments. However, in the first embodiment, a pair of prisms are used as beam center position adjusting means and a spherical lens is used as beam shape matching means, whereas in the third embodiment, beam center position adjusting means and beam shape matching means are used. Only in that a pair of diffraction lenses 71 and 72 are used. Therefore, in FIG. 7, the elements having the same functions as those of the first embodiment of FIG.
The same reference numerals as in FIG. 2 are assigned. Hereinafter, the third embodiment will be described by focusing on the differences from the first embodiment.

As shown in FIG. 7, in the third embodiment, the first
From the exit end of the fourth harmonic wave generating section 20
mm, and the second diffraction lens 72 is
At a distance of 120 mm from the first diffraction lens 71 and
At a distance of 53 mm from the incident end of the fifth harmonic wave generator 21
Are located. Note that a pair of diffraction lenses 71 and 7
The center of 2 is aligned with the beam center axis of the fourth harmonic
Positioned. Then, the first diffraction lens 71
Is f (ω) with respect to the fundamental wave (wavelength 1064 nm).₁) =
40 mm focal length, 4th harmonic (wavelength 266 nm)
F (4ω ₁) = Has a focal length of 160 mm
You. On the other hand, the second diffraction lens 72 has a fundamental wave (wavelength
64 nm) and f (ω₁) = 40mm focal length
F (4ω) for the fourth harmonic (wavelength 266 nm)₁)
= Has a focal length of 160 mm.

As described above, the diffractive lens (zone plate) is a diffractive optical element whose focal length is proportional to the reciprocal of the wavelength of the incident beam, that is, proportional to the frequency of the incident beam. Therefore, the fundamental wave (wavelength 1064)
focal length f for nm) (omega ₁₎ and fourth harmonic (wavelength 26
6 nm) and the focal length f (4ω ₁ )
The relationship of f (ω ₁ ) = f (4ω ₁ ) holds. Note that the numerical aperture NA is obtained by using the aperture diameter D ₀ and NA = D ₀ / (2
f). Therefore, between the numerical aperture NA (ω ₁ ) for the fundamental wave (wavelength 1064 nm) of the same diameter and the numerical aperture NA (4ω ₁ ) for the fourth harmonic (wavelength 266 nm), NA (ω ₁ ) = 4NA (4ω). ₁ ) is established. On the other hand, the spot size d at the focal point is d = λ / NA∝1 / (ω · NA), where λ is the wavelength of light. Accordingly, the spot size d (ω ₁ ) of the fundamental wave (wavelength 1064 nm) of the same aperture is equal to the spot size d (4ω ₁ ) of the fourth harmonic (wavelength 266 nm), and d
It is characterized in that the relationship of (ω ₁ ) = d (4ω ₁ ) holds.

Further, by adjusting the distance between the two diffractive lenses 71 and 72, the rear focal position of the pair of diffractive lenses is adjusted, and the rear focal position with respect to the fundamental wave is generated by the fifth harmonic. It is possible to match the center position of the BBO crystal of the part 21 and set the rear focal position for the fourth harmonic to the fourth harmonic generation part side by a predetermined distance from the central position of the BBO crystal of the fifth harmonic generation part 21. it can. As a result, the pair of diffraction lenses 71 and 72 match the beam shape of the fundamental wave and the beam shape of the fourth harmonic near the focal point of the fundamental wave. The beam vertically incident on the diffraction lens 71 is collected at the focal point on the optical axis (the center position of the BBO crystal of the fifth harmonic generation unit 21) without depending on the incident position on the diffraction lens 71. For this reason, the beam center position of the fundamental wave that is shifted from the center of the diffraction lens 71 substantially coincides with the beam center position of the fourth harmonic on the optical axis at the center position of the BBO crystal of the fifth harmonic generation unit 21. As described above, the pair of diffractive lenses 71 and 72 can simultaneously perform the function of the beam center position adjusting unit and the function of the beam shape matching unit in the BBO crystal of the fifth harmonic generation unit 21.

Therefore, as shown in FIGS. 7A to 7C, the diameter of 200 μm eccentric from the center axis of the beam of the fourth harmonic by 350 μm at the exit end of the fourth harmonic generator 20.
Is shaped into a beam shape having a diameter of about 180 μm about a beam center axis of the fourth harmonic at a position about 58 mm behind the second diffraction lens 72, that is, at the center position of the BBO crystal of the fifth harmonic generation unit 21. Is done. On the other hand, the fourth harmonic having a beam shape of 900 μm in the x direction and 200 μm in the y direction at the exit end of the fourth harmonic generator 20 also has the beam center of the fourth harmonic at the center position of the BBO crystal of the fifth harmonic generator 21. The beam is shaped into a beam having a diameter of about 180 μm about the axis. Thus, in the third embodiment, it is possible to realize good beam overlap between the fundamental wave and the fourth harmonic over the entire area from the incident end to the exit end of the BBO crystal of the fifth harmonic generation unit 21. it can.

In the above-described first and second embodiments, a pair of prisms or parallel flat plates as beam center position adjusting means is provided in the optical path between the second harmonic wave generating section and the fourth harmonic wave generating section 20. A face plate is arranged, but the fourth harmonic wave generating units 20 and 5
A beam center position adjusting means may be arranged in the optical path between the harmonic wave generating unit 21 and the harmonic wave generating unit 21. However, in this case, a beam having a short wavelength (for example, an ultraviolet beam) generated by the fourth harmonic generation unit 20 is transmitted through the beam center position adjusting means, so that an optical material which does not cause a problem of light absorption. You have to choose. In other words, arranging the beam center position adjusting means in the optical path between the second harmonic wave generating section and the fourth harmonic wave generating section 20 has an advantage that the range of selection of an optical material to be used is increased.

In the second embodiment, a pair of cylindrical lenses are used as beam shape matching means.
An aspheric lens having different refractive powers in the x direction and the y direction can also be used. Further, in each of the above-described embodiments, a pair of BBOs whose crystal axes are inverted in the fourth harmonic wave generation unit 20 are used.
Although a crystal is used, it is clear that the present invention can be realized even if the fourth harmonic wave generating section 20 is formed by one BBO crystal. Further, in each of the above-described embodiments, the present invention has been described by taking the wavelength converter for generating the fifth harmonic as an example. However, the present invention is not limited to the wavelength converter for generating the fifth harmonic, The present invention can be generally applied to a wavelength converter that generates a laser beam having a frequency (ω ₁ + 2ω ₂ ) based on a laser beam having a frequency ω _{1 and} a laser beam having a frequency ω ₂ .

FIG. 8 is a perspective view schematically showing the structure of one embodiment of an ultraviolet laser device using the wavelength converter of the present invention. This embodiment is an example in which the device of the present invention is applied to the wavelength conversion device disclosed in Japanese Patent Application Laid-Open No. 8-334803 filed by the present applicant. As shown in FIG.
The ultraviolet laser device 80 of the present embodiment includes 100 laser units 83 arranged vertically and horizontally in parallel. Each laser unit 83 has a semiconductor laser-excited solid-state laser device 81 and a wavelength converter 82 for converting the wavelength of the oscillation laser light from the laser device 81 into ultraviolet laser light. As the wavelength conversion device 82, for example, the wavelength conversion devices according to the above-described first to third embodiments can be used.

In this embodiment, the solid-state laser medium of the semiconductor laser-excited solid-state laser device 81 is, for example, Nd: YA.
G can be used. In this case, about 808 depending on the absorption spectrum of the laser medium (ie, Nd: YAG).
A laser diode having a wavelength of 1064 nm can be oscillated from the semiconductor laser-excited solid-state laser device 81 using a laser diode that supplies excitation light of 10 nm. 106 oscillated from the semiconductor laser pumped solid-state laser device 81
The near-infrared laser light of 4 nm is wavelength-converted through, for example, a wavelength converter 82 having a fifth harmonic generation action, and
An ultraviolet laser beam having a wavelength of nm is output from each laser unit 83. The ultraviolet laser light output from each laser unit 83 is coupled (coaxially) along the same optical path by optical coupling means not shown.

In the ultraviolet laser device 80 of the present embodiment, even if the output of the ultraviolet laser light from each laser unit 83 is small, the required number of parallelly arranged (in this embodiment, 100
), The ultraviolet laser light output from the laser units 83 is optically coupled, so that the output of the finally obtained ultraviolet laser light can be increased. Further, in the ultraviolet laser device 80 of the present embodiment, since the ultraviolet laser lights output from the plurality of laser units 83 arranged in parallel are optically coupled, the coherence of the finally obtained ultraviolet laser light is reduced. can do. As a result, in the present embodiment, for example, an ultraviolet laser device having a sufficient output and low coherence as a light source of a semiconductor exposure apparatus can be realized.

[0046]

As described above, according to the wavelength converter of the present invention, even if the beam diameter of the fundamental wave is set small,
By the operation of the beam center position adjusting means and the beam shape matching means, the influence of the walk-off in the BBO crystal of the fourth harmonic generation part is compensated, and the fundamental wave and the fourth harmonic are eliminated in the BBO crystal of the fifth harmonic generation part. Good beam overlap can be ensured. Further, the beam center position adjusting means and the beam shape matching means can be compactly arranged in a straight line together with the second harmonic wave generating unit, the fourth harmonic wave generating unit and the fifth harmonic wave generating unit. Therefore, according to the present invention, it is possible to realize a wavelength converter having a high wavelength conversion efficiency and a compact configuration without requiring a laser beam having a high peak output as a fundamental wave.

For example, an ultraviolet laser device can be constructed by arranging a plurality of laser units having a semiconductor laser pumped solid-state laser device and the wavelength converter of the present invention in parallel. In this case, when the ultraviolet laser light output from each laser unit is optically coupled, the output of the finally obtained ultraviolet laser light can be increased and the coherence can be reduced. As a result, the ultraviolet laser device of the present invention can supply an ultraviolet laser beam having sufficient output and low coherence as a light source of a semiconductor exposure apparatus, for example.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams for explaining the operation of a wavelength conversion device according to the present invention, in which FIG. 1A shows a state in which each laser beam propagates through the device, and FIG. Fundamental wave and 4
(C) shows the overlap between the fundamental wave and the fourth harmonic in the BBO crystal of the fifth harmonic generation part.

FIG. 2 is a diagram schematically illustrating a configuration of a wavelength conversion device according to a first embodiment of the present invention.

FIG. 3 is a diagram for explaining an influence of a walk-off in a fourth harmonic generation unit 20 according to the first embodiment.

FIG. 4 is a diagram for explaining the operation of a pair of prisms 24 and 25 constituting a beam center position adjusting means in the first embodiment.

FIG. 5 is a view for explaining a modification in which a parallel plane plate is used as a beam center position adjusting means in the first embodiment.

FIG. 6 is a diagram schematically showing a configuration of a wavelength converter according to a second embodiment of the present invention.

FIG. 7 is a diagram schematically showing a configuration of a wavelength converter according to a third embodiment of the present invention.

FIG. 8 is a perspective view schematically showing a configuration of an example of an ultraviolet laser device using the wavelength conversion device of the present invention.

FIG. 9 is a diagram showing a state of generation of a fourth harmonic in a nonlinear optical crystal BBO constituting a fourth harmonic generation part of a conventional wavelength conversion device, where (a) shows a state in which each laser beam propagates through the BBO crystal. (B) shows the beam position and beam shape of each laser beam at the exit end of the BBO crystal.

10A and 10B are diagrams showing a state in which a pair of BBO crystals whose crystal axes are inverted in a conventional wavelength converter are arranged in series to constitute a fourth harmonic wave generating unit, and FIG. (B) shows the state of propagation of the BBO crystal of
The beam position and beam shape of each laser beam at the exit end of the O crystal are shown.

[Explanation of symbols]

 Reference Signs List 20 fourth harmonic generator 21 fifth harmonic generator 22, 23 BBO crystal 24, 25 prism 26 spherical lens 51 parallel plane plate 61, 62 cylindrical lens 71, 72 diffractive lens 80 ultraviolet laser device 81 semiconductor laser-excited solid-state laser device 82 Wavelength converter 83 Laser unit

Claims (9)

[Claims] A first nonlinear optical crystal having birefringence, and a frequency ω ₁ incident on the first nonlinear optical crystal.
And the laser beam is transmitted without changing its frequency and emitted, and the frequency 2ω ₂ whose beam shape extends in a predetermined direction based on the laser beam of frequency ω ₂ incident as ordinary light on the first nonlinear optical crystal. A second harmonic generation means for generating and emitting the extraordinary light, and a second nonlinear optical crystal having birefringence, and the second nonlinear optical crystal is connected to the second nonlinear optical crystal via the first nonlinear optical crystal. Based on the incident laser light of frequency ω _{1 and} the laser light of frequency 2ω ₂ incident on the second nonlinear optical crystal via the first nonlinear optical crystal, the frequency (ω ₁ +
Sum frequency generation means for generating and emitting a laser beam of 2ω ₂ ), a beam center position of the laser beam of the frequency ω ₁ and a beam center position of the laser beam of the frequency 2ω ₂ in the second nonlinear optical crystal. and a beam center position adjusting means for substantially coincident with the common optical elements, and the beam shape of the frequency omega ₁ of the laser light beam shape and the laser light of the frequency 2 [omega ₂ in the second nonlinear optical crystal And a beam shape matching means for matching by using a common optical element. 2. The beam center position adjusting means is disposed in an optical path on the incident side of the second harmonic generating means or in an optical path between the second harmonic generating means and the sum frequency generating means. The wavelength converter according to claim 1, further comprising a plane-parallel plate. 3. The beam center position adjusting means is disposed in an optical path on the incident side of the second harmonic generating means or in an optical path between the second harmonic generating means and the sum frequency generating means. The wavelength conversion device according to claim 1, further comprising a pair of prisms. 4. The apparatus according to claim 1, wherein said beam shape matching means has a lens disposed in an optical path between said second harmonic generation means and said sum frequency generation means. 2. The wavelength converter according to claim 1. 5. The wavelength converter according to claim 4, wherein the lens has different refractive powers in two planes orthogonal to each other including the optical axis. 6. The beam center position adjusting means and the beam shape matching means have a pair of diffractive optical elements arranged in an optical path between the second harmonic generation means and the sum frequency generation means. 2. The wavelength converter according to claim 1, wherein the focal length of each diffractive optical element is proportional to the frequency of the incident light. 7. It has a third nonlinear optical crystal having birefringence, and a frequency ω ₁ incident on the third nonlinear optical crystal.
To generate a laser beam of frequency 2 [omega ₁ based on the laser light further comprises a second second harmonic generator for emitted, the second second-harmonic generation unit, the laser light of the frequency 2 [omega ₁ the wavelength conversion device according to any one of claims 1 to 6, wherein the injection along the same optical path and the frequency omega ₁ of the laser beam as the laser beam of the frequency omega _2. 8. A laser unit comprising the wavelength conversion device according to claim 1 and a laser unit for supplying a laser beam having a predetermined frequency to the wavelength conversion device. A plurality of laser units, wherein each laser unit converts the wavelength of the laser light from the laser device into ultraviolet laser light in the wavelength conversion device and emits the laser light. 9. The semiconductor laser-excited solid-state laser device that performs laser oscillation by optically exciting a solid-state laser medium doped with Nd with a semiconductor laser, and the wavelength converter is the semiconductor laser-excited solid-state laser device. 9. The ultraviolet laser device according to claim 8, wherein the wavelength of the near-infrared laser light from the laser beam is converted into an ultraviolet laser light having a fifth harmonic thereof.