CN109491097B - Method for generating axisymmetric vector light beam based on crystal optical activity - Google Patents
Method for generating axisymmetric vector light beam based on crystal optical activityDownload PDFInfo
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- CN109491097B CN109491097BCN201910034350.2ACN201910034350ACN109491097BCN 109491097 BCN109491097 BCN 109491097BCN 201910034350 ACN201910034350 ACN 201910034350ACN 109491097 BCN109491097 BCN 109491097B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
- G02B27/0938—Using specific optical elements
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
- G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another
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Abstract
Description
Technical Field
The invention belongs to the field of optics, and particularly relates to a method for generating an axisymmetric vector beam based on the optical rotation of a crystal.
Background
The vector beams with axisymmetric polarization distribution are widely concerned due to the special space polarization distribution, and the tightly focused axisymmetric vector beams have a focusing radius exceeding the diffraction limit and an adjustable focal spot shape, and have important applications in the fields of laser processing, information storage, microscopic imaging, surface plasmon regulation, optical capture and control, particle acceleration and the like.
Methods for generating axisymmetric vector beams are mainly classified into an active method and a passive method: the active method is a method of adding a vector beam generated by a polarization selection element in a laser cavity, has better beam quality and higher efficiency, but is difficult to adjust the elements in the laser cavity and has lower flexibility; the passive method realizes polarization conversion outside a laser cavity, and generates axisymmetric vector beams by methods such as beam interference, a spatial division phase retarder, a spatial variable sub-wavelength grating, a liquid crystal device, a spatial light modulator and the like. These methods usually require multiple conversion elements, have low conversion efficiency and low damage threshold, and cannot be applied to high-power laser systems to generate high-intensity axisymmetric vector beams.
Disclosure of Invention
The invention provides a method for generating an axisymmetric vector beam based on the optical rotation of a crystal, which aims at solving the problems in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for generating an axisymmetric vector beam based on crystal optical activity, the method comprising the steps of:
step 1, selecting an optical rotation crystal, and designing a crystal element with a spiral structure according to an ambient temperature T, a wavelength lambda of a linearly polarized laser to be converted and an optical rotation rate alpha of the optical rotation crystal: establishing a Cartesian coordinate system, taking the optical axis of the optically active crystal as the z-axis, and defining the included angle theta between the projection of a vector on the x-y plane and the positive direction of the x-axis along the counterclockwise direction on the basis that the x-axis and the y-axis are mutually perpendicular in the plane perpendicular to the z-axis1Processing the optically active crystal into a crystal element of a helical structure having a circular bottom surface and a radius r1Coordinate of any point on the side surface satisfies x12+y12＝r12(ii) a Azimuth angle theta of point coordinate on upper surface1When the thickness of the helical crystal element is d ═ k θ1+d0Where k is 1/α, d0Is theta1Thickness of the helical-structured crystal element when 0 satisfies d0> 0, corresponding to an azimuth angle theta1After passing through the position, the incident light is polarized and rotated by an angle phi0＝α·z0；
And 4, enabling linear polarization laser to enter along the z-axis direction of the polarization rotating element, enabling the center point of a polarization laser spot to be coaxial with the center of the bottom surface of the polarization rotating element, and obtaining the required axisymmetric vector beam by adjusting the included angle between the polarization direction of the polarization laser and the x direction of the polarization rotating element.
The helical crystal element is a hollow cylinder structure, i.e. a helical crystal element x2+y2＜δ2Is partially removed, the hollow cylinder structure satisfies x2+y2＜δ2X and y are respectively outside the hollow column structureThe coordinate value of any point on the circle, wherein delta is less thanr 12% of the total number of the crystal elements, wherein δ is a value that does not affect the structure of the axisymmetric vector beam, and is determined according to the intensity distribution of the axisymmetric vector beam, and is smaller than the radius of the hollow part of the axisymmetric vector beam, and is generally smaller than the radius r of the bottom surface of thespiral crystal element 12% of the total.
And a polarizing plate is arranged between the linear polarization laser and the polarization rotating element, and the polarizing plate and the polarization rotating element are coaxially arranged.
In the step 1, the optically rotating crystal is a quartz crystal.
The reverse spiral element in thestep 2 is quartz glass.
The Semmil equation of the optical rotation rate of the optical crystal in the optical axis direction at room temperature in the step 1 is as follows:
where λ is in μm and α is in °/mm.
Compared with the prior art, the invention has the beneficial effects that:
1. the power is high, and the output of the high-power axisymmetric vector beam can be realized by selecting the optically active crystal material with high damage threshold. For example, the damage threshold of the quartz crystal can reach 10J/cm2(@1053nm)
2. The method has high efficiency, does not have diffraction and interference processes, and has higher efficiency of generating the axisymmetric vector light beam.
3. The device has few elements, can realize radial, angular and any axisymmetric vector beams by using a single element, and is simple to adjust.
4. The polarization rotation element is easy to process, the optical rotation crystal material is processed into a spiral structure, the thickness of the crystal is in millimeter order, the polarization rotation element is easy to process, for example, when lambda is 1053nm, the quartz crystal is used for manufacturing the polarization rotation element, and the thickness of the crystal is about 57-65 mm.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic view of a crystal element of a helical structure according to the present invention.
FIG. 2 is a schematic view of the structure of the reverse spiral element of the present invention.
FIG. 3 is a schematic diagram of a polarization rotator according to the present invention.
Fig. 4 is a schematic structural diagram of the conversion of linearly polarized light into an axisymmetric vector beam in the present invention.
Fig. 5 is a schematic diagram of the polarization distribution of an axisymmetric vector beam obtained in the present invention.
FIG. 6 is a schematic structural diagram ofembodiment 2 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience of description and for simplicity of description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.
Example 1
As shown in fig. 1 to 5, the present embodiment is a method for generating an axisymmetric vector beam based on the optical rotation of a crystal, the method comprising the steps of:
step 1, selecting a rotorAn optical crystal, according to the environment temperature T, the linear polarization laser wavelength λ to be converted and the optical rotation rate α of the optical crystal, a spiral structure crystal element 1 is designed: establishing a Cartesian coordinate system, taking the optical axis of the optically active crystal as the z-axis, and defining the included angle theta between the projection of a vector on the x-y plane and the positive direction of the x-axis along the counterclockwise direction on the basis that the x-axis and the y-axis are mutually perpendicular in the plane perpendicular to the z-axis1Processing an optically active crystal into a crystal element 1 of a spiral structure, the bottom surface of the crystal element 1 of a spiral structure being circular and having a radius r1Coordinate of any point on the side surface satisfies x12+y12＝r12(ii) a Azimuth angle theta of point coordinate on upper surface1When the thickness of the spiral-structure crystal element 1 is d ═ k θ1+d0Where k is 1/α, d0Is theta1Thickness of the helical-structured crystal element 1 when 0, d0> 0, corresponding to an azimuth angle theta1After passing through the position, the incident light is polarized and rotated by an angle phi0＝α·z0；
And 4, enabling the linear polarizedlaser 4 to enter along the z-axis direction of thepolarization rotating element 3, enabling the center point of the light spot of the polarizedlaser 4 to be coaxial with the center of the bottom surface of thepolarization rotating element 3, and adjusting the included angle between the polarization direction of the polarizedlaser 4 and the x direction of thepolarization rotating element 3 to obtain the requiredaxisymmetric vector beam 5.
Preferably, the helical crystal element 1 of the present embodiment has a hollow cylinder structure, and the hollow cylinder structure satisfies x2+y2＜δ2X and y are coordinate values of any point on the excircle of the hollow cylinder structure respectively, and delta is less than r1*2％。
Further preferably, in this embodiment, a polarizing plate 6 is provided between the linearly polarizedlaser beam 4 and thepolarization rotator 3, and the polarizing plate 6 is provided coaxially with thepolarization rotator 3.
Preferably, in step 1 of this embodiment, the optically active crystal is a quartz crystal.
Further preferably, instep 2 of this embodiment, the reverse spiral element is made of quartz glass.
As a further preference, in the present embodiment, the Semmil equation of the optical rotation rate of the optical crystal in the optical axis direction of the optical crystal at room temperature in step 1 is:
where λ is in μm and α is in °/mm.
As shown in FIG. 5, the angle between the polarization direction of the desired axisymmetric vector beam at any point on the cross section and the radial direction is
Adjusting the included angle between the linear polarization direction and the x direction
Under the condition of the parameter, after linearly polarized light passes through the polarization rotating element, the polarization of the photoelectric field at the position of the azimuth angle theta of the cross section of the light beam is rotated into
The generated axisymmetric vector beam is atThe included angle between the polarization direction of any point on the cross section and the radial direction is
For example
The polarization rotating element converts linearly polarized light into radially polarized light
γ＝90°-φ0The polarization rotating element converts linearly polarized light into angularly polarized light
In the present embodiment, theta1、θ2All define the angle between the projection of the vector on the x-y plane and the positive direction of the x-axis along the counterclockwise direction
Example 2
In this embodiment, a polarizing plate 6 is provided between the linearly polarizedlaser beam 4 and thepolarization rotator 3, and the polarizing plate 6 is provided coaxially with thepolarization rotator 3. The rest technical schemes are the same as the embodiment 1.
Although the present invention has been described in detail with respect to the above embodiments, it will be understood by those skilled in the art that modifications or improvements based on the disclosure of the present invention may be made without departing from the spirit and scope of the invention, and these modifications and improvements are within the spirit and scope of the invention.
Claims (3)
1. A method for generating an axisymmetric vector beam based on optical activity of a crystal, comprising the steps of:
step 1, selecting an optical rotation crystal, and designing a spiral structure crystal element (1) according to an ambient temperature T, a wavelength lambda of a linearly polarized laser to be converted and an optical rotation rate alpha of the optical rotation crystal: establishing a Cartesian coordinate system with the optical axis of the optically active crystal as the z-axis, the x-axis and the y-axis being perpendicular to each other in a plane perpendicular to the z-axis, on the basis of which a vector is defined in the x-y planeThe included angle between the projection of (a) and the positive direction of the x axis along the counterclockwise direction is theta1Processing an optically active crystal into a crystal element (1) of helical structure, the bottom surface of said crystal element (1) of helical structure being circular and having a radius r1Coordinates of any point on the side surface satisfy
Azimuth angle theta of point coordinate on upper surface1When the thickness of the helical crystal element (1) is d ═ k θ1+d0Where k is 1/α, d0Is theta1The thickness of the helical crystal element (1) when 0 is satisfied0> 0, corresponding to an azimuth angle theta1After passing through the position, the incident light is polarized and rotated by an angle phi0＝α·z0The optical crystal in the step 1 is a quartz crystal;
step 2, preparing a reverse spiral element (2) with the same refractive index as the spiral structure crystal element (1), wherein the upper surface of the reverse spiral element (2) is circular and the radius is r2(ii) a Coordinates of any point on the side surface satisfy
Azimuth angle of point coordinate on lower surface is theta2When the thickness of the reverse spiral element (2) is d' ═ k theta2+d1Where k is 1/α, d1Is theta2The height of the reverse spiral element (2) when equal to 0 satisfies d1The reverse spiral element in the step 2 is quartz glass more than 360/alpha;
step 3, gluing the upper surface of the spiral structure crystal element (1) with the lower surface of the reverse spiral element (2) to ensure theta in the spiral structure crystal element (1)1With respect to theta in the reverse spiral element (2)2The same positions are aligned to prepare a polarization rotating element (3), the polarization rotating element (3) is of a cylindrical structure, and the radius of the bottom surface is r3Said r1＝r2＝r3Height h ═ d of cylinder0+d1；
And 4, enabling the linearly polarized laser (4) to be incident along the z-axis direction of the polarization rotating element (3), enabling the central point of a light spot of the linearly polarized laser (4) to be coaxial with the center of the bottom surface of the polarization rotating element (3), obtaining a required axisymmetric vector beam (5) by adjusting an included angle between the polarization direction of the linearly polarized laser (4) and the x direction of the polarization rotating element (3), arranging a polarizing plate (6) between the linearly polarized laser (4) and the polarization rotating element (3), and enabling the polarizing plate (6) to be coaxial with the polarization rotating element (3).
2. The method for generating an axisymmetric vector light beam based on crystal optical activity according to claim 1, wherein said helical-structured crystal element (1) has a hollow cylinder structure satisfying x2+y2＜δ2X and y are coordinate values of any point on the excircle of the hollow cylinder structure respectively, and delta is less than r1*2％。
3. The method for generating an axisymmetric vector beam based on the optical rotation of a crystal according to claim 1, wherein the Semmil equation of the optical rotation in the direction of the optical axis of the optical crystal at room temperature in step 1 is:
where λ is in μm and α is in °/mm.
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| CN109870823B (en)* | 2019-04-03 | 2020-12-15 | 中国科学院理化技术研究所 | A polarized light intensity shaping device |
| CN115014532A (en)* | 2022-08-01 | 2022-09-06 | 中国工程物理研究院应用电子学研究所 | Three-dimensional polarization measurement system based on sub-wavelength unit structure |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1910522A (en)* | 2004-01-16 | 2007-02-07 | 卡尔蔡司Smt股份公司 | Polarization Modulating Optics |
| JP2011060870A (en)* | 2009-09-08 | 2011-03-24 | Nikon Corp | Polarization conversion unit, illumination optical system, aligner, and method of manufacturing device |
| CN102830499A (en)* | 2012-09-05 | 2012-12-19 | 山东大学 | Vector light field converter and polarized light converting method |
| CN107976821A (en)* | 2018-01-04 | 2018-05-01 | 中国人民解放军国防科技大学 | An optical converter from linearly polarized light to radially polarized light |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7414786B2 (en)* | 2004-01-12 | 2008-08-19 | University Of Rochester | System and method converting the polarization state of an optical beam into an inhomogeneously polarized state |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1910522A (en)* | 2004-01-16 | 2007-02-07 | 卡尔蔡司Smt股份公司 | Polarization Modulating Optics |
| JP2011060870A (en)* | 2009-09-08 | 2011-03-24 | Nikon Corp | Polarization conversion unit, illumination optical system, aligner, and method of manufacturing device |
| CN102830499A (en)* | 2012-09-05 | 2012-12-19 | 山东大学 | Vector light field converter and polarized light converting method |
| CN107976821A (en)* | 2018-01-04 | 2018-05-01 | 中国人民解放军国防科技大学 | An optical converter from linearly polarized light to radially polarized light |
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