CN103336367A - 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

The 3 d light fields regulation device

Technical field

The present invention relates to beam shaping, particularly a kind of 3 d light fields regulation device.

Background technology

In the last few years, the 3 d light fields of long depth of focus, sub-wavelength was owing to the application at aspects such as particulate control, materials processing, high resolution optical imagings is subjected to extensive concern.Radial polarisation light is eager to excel more than the transverse field component at the longitudinal field component at focus place under the condition that large-numerical aperture focuses on, and this specific character can be used on the high resolving power microscopic method, aspects such as fiber imprint lithography and nonlinear optics.

At present, domestic and international many scholars utilize Richards-Wolf vector diffraction Integral Theory the focus characteristics of vector beam to be carried out a large amount of research.It is zero zone that bottle beams refers to have in the direction of propagation of light beam intensity, and this extra-regional three dimensions all by high-intensity light field around.People such as Kozawa have analyzed the focus characteristics of dicyclo Laguerre Gauss radial polarisation light, find that the hollow ring hot spot appears in zone, focus place, i.e. light trapping phenomenon, and particulate can be bound in blackening zone, center (Opt.Lett.31 (7): 987-989).The scientific research personnel has done a lot of experimental studies to the production method of vector light beam since 1972.Mainly contain active and passive method.Active method master is that the resonator cavity by laser aid produces vector beam, and the device that passive method utilization has the space variable polarization characteristic changes polarization state, such as utilizing two 1/2 vertical wave plates to produce the radial polarisation vector beam.Utilize liquid crystal polarized converter to realize that the vector polarized light also is a kind of very common method.The scientific research personnel has also had been found that the method for multiple generation light trapping.The two bundle Bezier interferences of light that S.Chavez-Cerda etc. utilize the circumferential weld lens method to produce obtain bottle beams, however Bessel's optical efficiency very low (Chavez-Cerda, Tepichin et al.1998) that the circumferential weld lens method produces.B.P.S.Ahluwalia etc. utilize the bottle beams of gradient axes pyramid generation cycle reproduction, but this gradient axes pyramid is difficult for processing (Ahluwalia, Cheong et al.2006).Produce bessel beam and focus on the 3 d light fields of the long depth of focus of formation with axicon and lens combination.But because the influence of factors such as diffraction effect, the light on the light trapping inner shaft that this method produces is non-vanishing usually, and can have a speck.In addition, the light tweezer that this kind method obtains can not be regulated and control, and can't produce reconfigurable " light trapping ", " laser accunputure " and " optical channel " three kinds of light fields.Therefore studying a kind of tunable optical forceps device that can produce the sub-wavelength magnitude seems particularly important.

Chinese patent " can produce the new profile shaft pyramid of single bottle beams " and (CN102364376A), propose a kind of method that produces bottle beams.Remove an angles at a point in tradition axle pyramid bottom and the little axle pyramid of different bottom surfaces radius forms with a same bottom surface radius cylinder gummed that cuts out a small column at the center again, thereby but between axle pyramid and cylinder, form the cavity of receiving fluids.Behind the directional light vertical incidence axle pyramid, the overlapping part on meridian ellipse forms no diffraction Bezier district, inserts condenser lens in this district, forms hollow light in a segment distance thereafter.The size of the single bottle beams that produces can be regulated by controlling wherein the size of liquid refractivity.But its spot size that can reach can only reach the hundreds of micron dimension, also fails to reach the magnitude of handling the sub-wavelength fine particle.Chinese patent " devices of adjustable smooth tweezers " (CN1588177A) proposes to utilize the concentric phase regulator in controlled three zones that incident light is modulated, and produces the tunable optical tweezer with the object lens method of focusing again.Though this method can realize motion and the variation of light tweezers, this method does not adopt vector light beam focusing, and therefore the optical field distribution that obtains is unsatisfactory.

Summary of the invention

The present invention is intended to overcome above-mentioned the deficiencies in the prior art, and a kind of 3 d light fields regulation device is provided, and this device can be realized long depth of focus, sub-wavelength, the 3 d light fields that can control.

Technical solution of the present invention is as follows:

A kind of 3 d light fields regulation device, its characteristics are, this device comprises laser instrument, the beam direction that sends along this laser instrument is the coaxial polarizer successively, diffraction optical element, Fourier transform lens, the radial polarisation photoconverter, amplitude type zone plate and high-NA condenser lens, described diffraction optical element and radial polarisation photoconverter lay respectively at front focal plane and the back focal plane of described Fourier transform lens, described laser instrument, the polarizer, diffraction optical element and Fourier transform lens are for generation of linear polarization dicyclo light beam, it is radial polarisation dicyclo light beam that the radial polarisation photoconverter makes described linear polarization dicyclo optical beam transformation, described amplitude type zone plate and high-NA condenser lens carry out Modulation and Amplitude Modulation and convergence with described radial polarisation dicyclo light beam, near the focal plane of high-NA condenser lens, obtain long depth of focus, the 3 d light fields of sub-wavelength, described amplitude type zone plate is finished the regulation and control to described 3 d light fields.

Described radial polarisation photoconverter adopts the converter of liquid crystal type, and this converter has been ripe product.

When the polarization direction of described linear polarizer is vertical with the direction of radial polarisation photoconverter, obtain required radial polarisation light, when being parallel to each other, obtain the angle polarized light.

Described diffraction optical element is for generation of the dicyclo light beam, and the design of described diffraction optical element is based on (referring to the Optik, 35,237-246,1972) of GS algorithm design, and this algorithm is known by the researcher in this field.The size of described diffraction optical element is much larger than wavelength, and described linearly polarized light is behind diffraction optical element, and polarization state remains unchanged.

Described amplitude type zone plate and high-NA focus lens group share to produce tunable long depth of focus, sub-wavelength 3 d light fields, namely optical axis place longitudinal length greater than optical wavelength and sectional dimension less than optical wavelength.

The light beam that sends when described laser instrument forms linearly polarized light through linear polarizer.This linearly polarized light is modulated through described diffraction optical element, forms uniform dicyclo light beam.This dicyclo light beam is converted to radial polarisation dicyclo light beam through described radial polarisation photoconverter with linear polarization dicyclo light beam.Described amplitude type zone plate and described immersion high-NA condenser lens to the focusing of described dicyclo radial polarisation light, produce tunable long depth of focus, sub-wavelength 3 d light fields.

Described amplitude wave strap is realized the adjusting of near the optical axis place longitudinal length of described immersion high-NA condenser lens back focal plane and sectional dimension.Described amplitude type zone plate contains a plurality of concentric endless belt, and the transmission coefficient of each endless belt is 0 or 1.The radius of each endless belt and the adjusting that width can be realized light field longitudinal length and lateral dimension are set, thereby realize the adjusting of depth of focus and beam cross section size.

Compare with first technology, the present invention has following beneficial effect:

1, the present invention has realized the 3 d light fields regulation and control, and this 3 d light fields has the characteristics of long depth of focus, sub-wavelength, can regulate this 3 d light fields longitudinal length and lateral dimension by the endless belt parameter that changes the amplitude type zone plate.

2, the 3 d light fields regulation device that proposes of the present invention has simple in structurely, and the element cost is low, the advantage of easy operating.

Description of drawings

Fig. 1 is 3 d light fields regulation device principle assumption diagram of the present invention

Fig. 2 is described amplitude type zone plate endless belt design diagram

3 d light fields and regulation and control synoptic diagram thereof that Fig. 3 forms for 3 d light fields regulation device of the present invention

Embodiment

For making technical scheme of the present invention and advantage clear, below in conjunction with drawings and Examples the present invention is done to elaborate.

Please refer to accompanying drawing 1, accompanying drawing 1 is 3 d light fields regulation device principle assumption diagram of the present invention.3 d light fields regulation device of the present invention comprises laser instrument 101, the polarizer 201, diffraction optical element 301, Fourier transform lens 401, radial polarisation photoconverter 501, amplitude type zone plate 601 and high-NA condenser lens 701; Wherein dicyclo Laguerre Gaussian beam formation unit comprises: laser instrument 101, the polarizer 201, diffraction optical element 301 and Fourier transform lens 401.

The position relation of said elements is as follows:

Along the beam direction that described laser instrument 101 sends, be the coaxial polarizer 201, diffraction optical element 301, Fourier transform lens 401, radial polarisation photoconverter 501, amplitude type zone plate 601 and high-NA condenser lens 701 successively.Described diffraction optical element 301 and radial polarisation photoconverter 501 lay respectively at front focal plane and the back focal plane place of described Fourier transform lens 401.

When the polarization direction of the described polarizer 201 is vertical with the direction of radial polarisation photoconverter, obtain required radial polarisation light, when direction is parallel, obtain the angle polarized light.

Described diffraction optical element 301 is for generation of Laguerre Gauss dicyclo light beam, and do not change the polarization state of light beam.Described diffraction optical element is made of etching method after carrying out design of Simulation of computing machine.

The tunable long depth of focus of described amplitude type zone plate 601 and high-NA condenser lens 701 combination results, sub-wavelength 3 d light fields, namely optical axis place longitudinal length is greater than optical wavelength, and sectional dimension is less than optical wavelength.

The light beam that sends when described laser instrument 101 forms linearly polarized light through the described polarizer 201.This linearly polarized light forms even dicyclo light beam through the modulation of described diffraction optical element 301.This dicyclo light beam is converted to radial polarisation light by described radial polarisation photoconverter 501 with linearly polarized light at back focal plane behind described fourier transform lens 401.Described radial polarisation photoconverter 501 is liquid crystal polarized converter, by regulating alive size, can obtain radial polarisation, angle polarization and vortex polarization.Described amplitude type zone plate 601 and high-NA condenser lens 701 are realized the radially tight focusing of polarized light, and described amplitude type zone plate 601 is realized the adjusting of lens back focal plane optical axis place longitudinal component.The transmission coefficient of each endless belt of amplitude type zone plate 601 is 0 or 1, in order to the spatial frequency spectrum component of selecting to see through.Can design three or five or more endless belt according to the experiment needs, transmitance is respectively 0 or 1.

Described diffraction optical element 301 is used for obtaining required dicyclo light beam, and the design of described diffraction optical element 301 is based on (referring to the Optik, 35,237-246,1972) of GS algorithm design, and this algorithm is that the researcher in this field is known.

A kind of structure of available described amplitude type zone plate 601 as shown in Figure 2.(Amplitude zone plate, sectional view AZP) are shown in 601-2 among Fig. 2, and white portion is the transparent zone territory, and black region is the zone of being in the light for described amplitude type zone plate.601 and 701 are respectively described amplitude type zone plate and described high-NA condenser lens.The parameter of indicating among the figure will be described below.

The parameter-definition that follow-up theoretical derivation is used is as follows:

1) light beam relative size parameter beta is described ₀

${\mathrm{\β}}_0=\frac{D_{\mathrm{IFL}}}{D_o}---\left(1\right)$

In the formula, D _IFLBe the clear aperture of described high-NA condenser lens 701, D ₀It is the outer shroud overall diameter of described dicyclo light beam.

2) through after described high-NA condenser lens 701 convergences, the convergent angle θ of light

$\mathrm{\θ}=\frac{r_{\mathrm{AZP}}}{d_{\mathrm{AZP}}}---\left(2\right)$

R in the formula _AZPBe certain any radius on the described amplitude type zone plate 601, d _AZPBe that described amplitude type zone plate 601 is to the distance of described high-NA condenser lens 701 back focal planes.

The optical field distribution of Laguerre Gauss dicyclo light beam can be expressed as:

$L(x,y)=\frac{{{\mathrm{\β}}_0}^2\sqrt{x^2+y^2}}{\mathrm{fsi}{n}^2\mathrm{\α}}\·\exp [-{\left(\frac{{\mathrm{\β}}_0\sqrt{x^2+y^2}}{f\sin \mathrm{\α}}\right)}^2]\·[2-2\left(\frac{{\mathrm{\β}}_0\sqrt{x^2+y^2}}{f\sin \mathrm{\α}}\right)]---\left(3\right)$

Wherein, x and y are volume coordinate, and f is the focal length of high-NA condenser lens.

The Laguerre Gauss dicyclo radial light field distribution that described diffraction optical element produces is write as polar form and is:

$L_p\left(\mathrm{\θ}\right)={\mathrm{\β}}_0^2(\sin \mathrm{\θ}/\mathrm{si}{n}^2\mathrm{\α})\exp [-{\left(\frac{{\mathrm{\β}}_0\sin \mathrm{\θ}}{\sin \mathrm{\α}}\right)}^2]L_p^1\left[2{\left(\frac{{\mathrm{\β}}_0\sin \mathrm{\θ}}{\sin \mathrm{\α}}\right)}^2\right]---\left(4\right)$

Wherein, a is maximum half aperture angle, and a=arcsin (NA/n), n are the refractive indexes that immerses medium.θ represents the angle of converging of light.L _pBe to be generalized Laguerre polynomial, when calculating the dicyclo light beam, p is 1.

According to the fertile husband's theory (Opt.Express7,77 (2000)) of Richard, behind described Laguerre Gauss dicyclo radial polarized light beam process amplitude type zone plate 601 and the high-NA condenser lens 701,

Radial component and longitudinal component at the focal plane place are respectively:

$E_r(r,z)=\underset{{\mathrm{\θ}}_1}{\overset{{\mathrm{\θ}}_2}{\∫}}{L}_1^1\left(\mathrm{\θ}\right)\sin 2\mathrm{\θ}\sqrt{\cos \mathrm{\θ}}{J}_1\left(\mathrm{kr}\sin \mathrm{\θ}\right)e^{\mathrm{ikz}\cos \mathrm{\θ}}\mathrm{d\θ}---\left(5\right)$

$E_z(r,z)=i\underset{{\mathrm{\θ}}_1}{\overset{{\mathrm{\θ}}_2}{\∫}}{L}_1^1\left(\mathrm{\θ}\right)\sin 2\mathrm{\θ}\sqrt{\cos \mathrm{\θ}}{J}_0\left(\mathrm{kr}\sin \mathrm{\θ}\right)e^{\mathrm{ikz}\cos \mathrm{\θ}}\mathrm{d\θ}---\left(6\right)$

Wherein, θ ₁, θ ₂Little subtended angle and the large angle of representing bright ring respectively, as shown in Figure 2.Then total light intensity can be represented with following formula:

I＝|E _r| ²+|E _z| ² (7)

Work as θ ₁, θ ₂When getting suitable value, near the 3 d light fields that can obtain three kinds of shapes such as light trapping, laser accunputure, light channel structure the back focal plane of high-NA condenser lens 701 distributes.

The ratio of the radius of described high-NA focusing objective len 701 and incident beam external radius is namely tackled β ₀Suitable value need be arranged.The tight focalizer of described dicyclo radial polarized light beam can be realized bottle beams and laser accunputure etc., and this performing step is as follows:

1. the polarizer 201 of correspondence and diffraction optical element 301 are fixed on corresponding position, contour coaxial with laser instrument 101 beam outlet;

2. start laser instrument 101;

3. mobile Fourier transform lens 401 utilizes methods such as shear interference to determine described Fourier transform lens 401 positions, and making output beam is directional light;

4. in light path, add liquid crystal radial polarisation photoconverter 501, regulate height and the position of radial polarisation photoconverter 501, make it to be in the back focal plane place of Fourier transform lens 401.

5. in light path, add amplitude type polaroid and high-NA condenser lens 701.Regulate receiving screen 801 along line slideway, fix at the back focal plane place of described high-NA condenser lens 701.

6. the CCD probe is placed in described receiving screen 801 places.Regulate the voltage of liquid crystal polarization converter 501, can regulate the polarization characteristic of output beam, realize that linearly polarized light is to the conversion of radial polarisation light.The size of regulating each endless belt of amplitude type zone plate 601 can change 3 d light fields longitudinal length and lateral dimension.

See also Fig. 2,102 have provided described amplitude type zone plate front elevation among Fig. 2.Wherein laser instrument 101 output light-wave wavelength are 632.8nm.Outgoing beam becomes the dicyclo light beam behind diffraction element 301, become directional light output again after Fourier transform lens converges.The dicyclo light beam of this parallel incident forms the dicyclo radial polarized light beam after changing by radial polarisation photoconverter 501.Dicyclo radially light beam is regulated by amplitude type zone plate 202, by high-NA condenser lens 302 forms at the back focal plane place as shown in Figure 3 difformity and the 3 d light fields distribution of size.In the present embodiment, the radius ratio of high numerical aperture lens 302 and dicyclo light beam outer shroud is β ₀=1.3, NA is 1.4.What described high numerical aperture lens adopted is the microcobjective (Plan Apochromat63x/1.4NA Oil is referring to www.zeiss.de/highres) of Zeiss company.

Described zone plate is the tricyclic structure shown in the 601-2 among Fig. 2, according to formula (5-7), can calculate near the optical field distribution of high-NA condenser lens focal plane.Work as θ ₁=0, θ ₂=0.2 o'clock, obtain the light field structure shown among Fig. 3 103, this figure horizontal ordinate is represented the direction of light transmission, and ordinate is represented the direction perpendicular to the light transmission, and the white representative has the light zone among the figure, and black represents unglazed zone, and represents the power of light by shade; Work as θ ₁=0.2, θ ₂, obtain the light field structure shown among Fig. 3 203 at=0.6 o'clock; Work as θ ₁=0.9, θ ₂, obtain the light field structure shown among Fig. 3 303 at=1 o'clock.This embodiment shows that this device can be by near the light field regulation and control the structure realization high-NA condenser lens focal plane of regulating amplitude type zone plate 501, and controlling the field at optics processing, detection and particle has potential using value.

Claims (1)

1. 3 d light fields regulation device, it is characterized in that, this device comprises laser instrument (101), the beam direction that sends along this laser instrument (101) is the coaxial polarizer (201) successively, diffraction optical element (301), Fourier transform lens (401), radial polarisation photoconverter (501), amplitude type zone plate (601) and high-NA condenser lens (701), described diffraction optical element (301) and radial polarisation photoconverter (501) lay respectively at front focal plane and the back focal plane of described Fourier transform lens (401), described laser instrument, the polarizer, diffraction optical element and Fourier transform lens are for generation of linear polarization dicyclo light beam, it is radial polarisation dicyclo light beam that the radial polarisation photoconverter makes described linear polarization dicyclo optical beam transformation, described amplitude type zone plate and high-NA condenser lens carry out Modulation and Amplitude Modulation and convergence with described radial polarisation dicyclo light beam, near the focal plane of high-NA condenser lens, obtain long depth of focus, the 3 d light fields of sub-wavelength, described amplitude type zone plate is finished the regulation and control to described 3 d light fields.

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