CN103336367B - Three-dimensional optical field adjusting and controlling device - Google Patents

Abstract

A three-dimensional optical field adjusting and controlling device comprises a laser, wherein a polarizer, a diffraction optical element, a Fourier transforming lens, a radial polarized light converter, an amplitude type wave zone plate and a highly-numerical aperture focusing lens are coaxially arranged in sequence in the direction of a light beam emitted by the laser; the diffraction optical element and the radial polarized light converter are respectively arranged on the front focal plane and the rear focal plane of the Fourier transforming lens. The three-dimensional optical field adjusting and controlling device can achieve a three-dimensional optical field with long focal depth, sub-wavelength and controllability.

Description

Three-dimensional light field control device

technical field

The invention relates to beam shaping, in particular to a three-dimensional light field regulating device.

Background technique

In recent years, the long focal depth and sub-wavelength three-dimensional light fields have attracted extensive attention due to their applications in particle control, material processing, and high-resolution optical imaging. When radially polarized light is focused at a large numerical aperture, the longitudinal field component at the focal point is much stronger than the transverse field component. This characteristic can be used in high-resolution microscopy, fiber lithography, and nonlinear optics.

At present, many scholars at home and abroad have done a lot of research on the focusing characteristics of vector beams by using the Richards-Wolf vector diffraction integral theory. The local hollow beam refers to a region with zero intensity in the propagation direction of the beam, and the three-dimensional space outside this region is surrounded by a high-intensity light field. Kozawa et al. analyzed the focusing characteristics of double-ring Laguerre-Gaussian radially polarized light, and found that a hollow ring-shaped spot appeared in the focus area, that is, the light trap phenomenon, and particles could be bound in the central dark spot area (Opt.Lett.31(7) :987-989). Since 1972, researchers have done a lot of experimental research on the method of generating vector polarized beams. There are mainly active and passive methods. The active method is mainly to generate a vector beam through the resonator of the laser device, and the passive method uses a device with spatially variable polarization characteristics to change the polarization state, such as using two vertical 1/2 wave plates to generate a radially polarized vector beam. It is also a very common method to realize vector polarized light by using a liquid crystal polarization converter. Researchers have also discovered a variety of ways to create light traps. S.Chavez-Cerda et al. used the interference of two beams of Bessel light produced by the annular slit lens method to obtain a local hollow beam, but the Bessel light efficiency produced by the annular slit lens method was very low (Chavez-Cerda, Tepichin et al.1998 ). B.P.S. Ahluwalia et al. used gradient axicons to generate periodically recurring local hollow beams, but such gradient axicons are not easy to process (Ahluwalia, Cheong et al.2006). Bessel beams are generated and focused by an axicon and lens system to form a three-dimensional light field with a long focal depth. However, due to factors such as diffraction effects, the light on the inner axis of the light trap produced by this method is usually not zero, but a bright spot exists. In addition, the optical tweezers obtained by this method are not controllable, and cannot generate reconfigurable optical fields of "optical trap", "optical needle" and "optical channel". Therefore, it is particularly important to study a tunable optical tweezers device that can generate subwavelength levels.

The Chinese patent "A new type of axicon that can generate a single local hollow beam" (CN102364376A) proposes a method for generating a local hollow beam. A small axicon with the same apex angle but different base radii is removed from the bottom of the traditional axicon, and then glued together with a cylinder with the same base radius and a small cylinder dug out in the center, so that a liquid can be accommodated between the axicon and the cylinder. cavity. After the parallel light is vertically incident on the axicon, the overlapping part on the meridian plane forms a non-diffraction Bessel area, and a focusing lens is inserted in this area to form a hollow light in a certain distance thereafter. The size of the generated single localized hollow beam can be tuned by controlling the refractive index of the liquid in it. However, the spot size it can achieve can only reach the order of hundreds of microns, and it has not yet reached the order of manipulating sub-wavelength tiny particles. The Chinese patent "A device for adjustable optical tweezers" (CN1588177A) proposes to use a controllable three-region concentric phase regulator to modulate the incident light, and then use an objective lens to focus to produce adjustable optical tweezers. Although this method can realize the movement and change of optical tweezers, but this method does not use vector beam focusing, so the obtained optical field distribution is not ideal.

Contents of the invention

The present invention aims to overcome the shortcomings of the above-mentioned prior art, and provides a three-dimensional light field control device, which can realize a long focal depth, sub-wavelength, and controllable three-dimensional light field.

Technical solution of the present invention is as follows:

A three-dimensional light field regulating device is characterized in that the device includes a laser, and along the direction of the light beam emitted by the laser is a coaxial polarizer, a diffractive optical element, a Fourier transform lens, a radially polarized light converter, The amplitude type zone plate and the high numerical aperture focusing lens, the diffractive optical element and the radial polarization converter are respectively located on the front focal plane and the back focal plane of the Fourier transform lens, the laser, the starting A polarizer, a diffractive optical element and a Fourier transform lens are used to generate a linearly polarized double-ring beam, and a radial polarization converter transforms the linearly polarized double-ring beam into a radially polarized double-ring beam, and the amplitude-type zone plate and a high numerical aperture focusing lens to perform amplitude modulation and convergence on the radially polarized double-ring light beam, and obtain a three-dimensional light field with a long focal depth and sub-wavelength near the focal plane of the high numerical aperture focusing lens, and the amplitude-type waveband The slice completes the regulation of the three-dimensional light field.

The said radially polarized light converter adopts a liquid crystal type converter, which is already a mature product.

When the polarization direction of the linear polarizer is perpendicular to the direction of the radial polarization converter, the desired radially polarized light is obtained, and when they are parallel to each other, angularly polarized light is obtained.

The diffractive optical element is used to generate double-ring beams, and the design of the diffractive optical element is based on the GS algorithm (see Optik, 35, 237-246, 1972), which is well known to researchers in the field. The size of the diffractive optical element is much larger than the wavelength, and the polarization state of the linearly polarized light remains unchanged after passing through the diffractive optical element.

The combination of the amplitude type zone plate and the high numerical aperture focusing lens is used to generate a tunable long focal depth, sub-wavelength three-dimensional light field, that is, the longitudinal length at the optical axis is larger than the light wavelength and the cross-sectional size is smaller than the light wavelength.

When the light beam emitted by the laser passes through the linear polarizer, linearly polarized light is formed. The linearly polarized light is modulated by the diffractive optical element to form a uniform double-ring light beam. The double-ring light beam is converted into a radially polarized double-ring light beam by the radially polarized light converter. The amplitude-type zone plate and the immersion-type high-numerical-aperture focusing lens focus on the double-ring radially polarized light to generate a tunable three-dimensional light field with a long focal depth and a sub-wavelength.

The amplitude zone plate realizes the adjustment of the longitudinal length and cross-sectional size at the optical axis near the rear focal plane of the submerged high numerical aperture focusing lens. The amplitude-type zone plate contains a plurality of concentric annular zones, and the transmission coefficient of each annular zone is 0 or 1. Setting the radius and width of each annular zone can realize the adjustment of the longitudinal length and lateral size of the light field, thereby realizing the adjustment of the depth of focus and the cross-sectional size of the beam.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention realizes the control of three-dimensional light field. The three-dimensional light field has the characteristics of long focal depth and sub-wavelength, and the longitudinal length and lateral dimension of the three-dimensional light field can be adjusted by changing the ring parameters of the amplitude-type zone plate.

2. The three-dimensional light field regulating device proposed by the present invention has the advantages of simple structure, low component cost and easy operation.

Description of drawings

Fig. 1 is the schematic structural diagram of the three-dimensional light field control device of the present invention

Figure 2 is a schematic diagram of the design of the amplitude-type zone plate annulus

Figure 3 is a schematic diagram of the three-dimensional light field formed by the three-dimensional light field control device of the present invention and its control

Detailed ways

In order to clarify the technical solutions and advantages of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Please refer to accompanying drawing 1, which is a schematic structural diagram of the three-dimensional light field control device of the present invention. The three-dimensional light field control device of the present invention includes a laser 101, a polarizer 201, a diffractive optical element 301, a Fourier transform lens 401, a radial polarization converter 501, an amplitude type zone plate 601 and a high numerical aperture focusing lens 701; The double-ring Laguerre-Gauss beam forming unit includes: a laser 101 , a polarizer 201 , a diffractive optical element 301 and a Fourier transform lens 401 .

The positional relationship of the above components is as follows:

Along the beam direction emitted by the laser 101, there are coaxial polarizer 201, diffractive optical element 301, Fourier transform lens 401, radial polarization converter 501, amplitude type zone plate 601 and high numerical value Aperture focusing lens 701 . The diffractive optical element 301 and the radial polarization converter 501 are respectively located at the front focal plane and the back focal plane of the Fourier transform lens 401 .

When the polarization direction of the polarizer 201 is perpendicular to the direction of the radial polarization converter, desired radially polarized light is obtained, and when the directions are parallel, angularly polarized light is obtained.

The diffractive optical element 301 is used to generate a Laguerre-Gauss double ring beam without changing the polarization state of the beam. The diffractive optical element is designed by computer simulation and then manufactured by etching.

The combination of the amplitude-type zone plate 601 and the high numerical aperture focusing lens 701 produces a tunable long-focus, sub-wavelength three-dimensional light field, that is, the longitudinal length at the optical axis is greater than the light wavelength, and the cross-sectional size is smaller than the light wavelength.

When the light beam emitted by the laser 101 passes through the polarizer 201 , linearly polarized light is formed. The linearly polarized light is modulated by the diffractive optical element 301 to form a uniform double-ring beam. After the double ring light beam passes through the Fourier lens 401, the linearly polarized light is converted into radially polarized light by the radially polarized light converter 501 at the rear focal plane. The radial polarization converter 501 is a liquid crystal polarization converter, and radial polarization, angular polarization and vortex polarization can be obtained by adjusting the magnitude of the applied voltage. The amplitude-type zone plate 601 and the high numerical aperture focusing lens 701 realize tight focusing on radially polarized light, and the amplitude-type zone plate 601 realizes the adjustment of the longitudinal component at the optical axis of the rear focal plane of the lens. The transmission coefficient of each annular zone of the amplitude-type zone plate 601 is 0 or 1, which is used to select the transmitted spatial spectrum component. According to the needs of the experiment, three or five or more annular zones can be designed, and the transmittances are 0 or 1 respectively.

The diffractive optical element 301 is used to obtain the required double-ring beam, and the design of the diffractive optical element 301 is based on the GS algorithm design (see Optik, 35, 237-246, 1972), which is developed by researchers in the field. familiar.

An available structure of the amplitude-type zone plate 601 is shown in FIG. 2 . The sectional view of the amplitude zone plate (Amplitude zone plate, AZP) is shown as 601-2 in Fig. 2, the white area is the light-passing area, and the black area is the light-blocking area. 601 and 701 are the amplitude type zone plate and the high numerical aperture focusing lens respectively. The parameters noted in the figure are explained below.

The parameters used in the subsequent theoretical derivation are defined as follows:

1) Describe the beam relative size parameter β ₀

${\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; IFL</span>}}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, D _IFL is the clear aperture of the high numerical aperture focusing lens 701, and D ₀ is the outer diameter of the outer ring of the double ring light beam.

2) After being converged by the high numerical aperture focusing lens 701, the convergence angle θ of the light

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; AZP</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; AZP</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, r _AZP is the radius of a certain point on the amplitude type zone plate 601 , and d _AZP is the distance from the amplitude type zone plate 601 to the back focal plane of the high numerical aperture focusing lens 701 .

The light field distribution of a Laguerre-Gaussian double ring beam can be expressed as:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}{\mathrm{<span\; class="notranslate">\; in</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

where x and y are the spatial coordinates, and f is the focal length of the high numerical aperture focusing lens.

The Laguerre-Gauss double-ring radial light field distribution generated by the diffractive optical element is written in polar coordinate form as:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 2</span>}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them, a is the maximum semi-aperture angle, a=arcsin(NA/n), and n is the refractive index of the immersion medium. θ represents the convergence angle of light. L _p is a generalized Laguerre polynomial, when calculating the double ring beam, p is 1.

According to Richard Worf's theory (Opt.Express7,77 (2000)), after the Laguerre-Gauss double-ring radially polarized light beam passes through the amplitude type zone plate 601 and the high numerical aperture focusing lens 701, at the focal plane The radial and longitudinal components are:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; kr</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; ikz</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; i</span>}\underset{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\sqrt{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; kr</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; ikz</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}\mathrm{<span\; class="notranslate">\; d\&theta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Among them, θ ₁ and θ ₂ respectively represent the small opening angle and large opening angle of the bright ring, as shown in Fig. 2 . Then the total light intensity can be expressed by the following formula:

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; =</span>{{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

When θ ₁ and θ ₂ take appropriate values, three-dimensional light field distributions in three shapes such as optical trap, optical needle, and optical channel structure can be obtained near the rear focal plane of the high numerical aperture focusing lens 701 .

The ratio of the radius of the high numerical aperture focusing objective lens 701 to the outer radius of the incident light beam, that is, the interception β ₀ needs to have an appropriate value. The double-ring radially polarized beam tight focusing device can realize local hollow beams and light needles, etc., and the implementation steps are as follows:

① Fix the corresponding polarizer 201 and diffractive optical element 301 at the corresponding position, which is coaxial with the beam exit of the laser 101;

② Start the laser 101;

3. move the Fourier transform lens 401, determine the position of the Fourier transform lens 401 by methods such as shear interference, so that the output beam is parallel light;

④Add a liquid crystal radial polarization converter 501 in the optical path, adjust the height and position of the radial polarization converter 501 so that it is at the back focal plane of the Fourier transform lens 401 .

⑤ Adding an amplitude type polarizer and a high numerical aperture focusing lens 701 into the optical path. The receiving screen 801 is adjusted along a linear guide rail and fixed at the back focal plane of the high numerical aperture focusing lens 701 .

⑥ Place the CCD probe on the receiving screen 801 . By adjusting the voltage of the liquid crystal polarization converter 501 , the polarization characteristics of the output beam can be adjusted, and the conversion from linearly polarized light to radially polarized light can be realized. Adjusting the size of each annular zone of the amplitude-type zone plate 601 can change the longitudinal length and transverse dimension of the three-dimensional light field.

Please refer to FIG. 2 , 102 in FIG. 2 shows the front view of the amplitude-type zone plate. Wherein the laser 101 outputs light with a wavelength of 632.8nm. The outgoing light beam becomes a double-ring light beam after passing through the diffraction element 301, and then converged by a Fourier transform lens to output parallel light. The parallel incident double ring light beam is converted by the radial polarization converter 501 to form a double ring radially polarized light beam. The double-ring radial beam is adjusted by the amplitude zone plate 202, and the high numerical aperture focusing lens 302 forms three-dimensional light field distributions of different shapes and sizes at the back focal plane as shown in FIG. 3 . In this embodiment, the radius ratio between the high numerical aperture lens 302 and the outer ring of the double-ring beam is β ₀ =1.3, and the NA is 1.4. The high numerical aperture lens used is a Zeiss microscope objective lens (Plan Apochromat63x/1.4NA Oil, see www.zeiss.de/highres).

The zone plate is a three-ring structure shown in 601-2 in FIG. 2 . According to the formula (5-7), the light field distribution near the focal plane of the high numerical aperture focusing lens can be calculated. When θ ₁ =0, θ ₂ =0.2, the light field structure shown as 103 in Figure 3 is obtained. The abscissa of this figure indicates the direction of light transmission, and the ordinate indicates the direction perpendicular to the light transmission. The white color in the figure represents the direction of light transmission. In the light area, black represents the non-light area, and the intensity of light is represented by the color depth; when θ ₁ =0.2, θ ₂ =0.6, the light field structure shown in 203 in Figure 3 is obtained; when θ ₁ =0.9, When θ ₂ =1, the light field structure shown as 303 in FIG. 3 is obtained. This embodiment shows that the device can adjust the light field near the focal plane of the high numerical aperture focusing lens by adjusting the structure of the amplitude-type zone plate 501, and has potential application value in the fields of optical processing, detection and particle manipulation.

Claims (1)

1. A three-dimensional light field regulating device is characterized in that, the device comprises a laser (101), and the beam direction along the laser (101) is followed by a coaxial polarizer (201), a diffractive optical element (301) , Fourier transform lens (401), radial polarized light converter (501), amplitude type zone plate (601) and high numerical aperture focusing lens (701), described diffractive optical element (301) and radial The polarized light converter (501) is respectively positioned at the front focal plane and the rear focal plane of the Fourier transform lens (401), and the laser, polarizer, diffractive optical element and Fourier transform lens are used to generate The linearly polarized double-ring beam, the radially polarized light converter transforms the linearly polarized double-ring beam into a radially polarized double-ring beam, and the amplitude type zone plate and high numerical aperture focusing lens transform the radially polarized double-ring beam Amplitude modulation and convergence are performed to obtain a long focal depth and sub-wavelength three-dimensional light field near the focal plane of a high numerical aperture focusing lens. The amplitude-type zone plate completes the regulation of the three-dimensional light field, and the The high numerical aperture focusing lens has a numerical aperture of 1.4.