Composite structure vector vortex light field regulation and control system based on BBO crystal second harmonics

Abstract

The invention discloses a composite structure vector vortex light field regulation and control system based on BBO crystal second harmonics, and the system comprises a laser which is used for transmitting laser and enabling the laser to enter a beam expanding lens; the first collimating lens is used for collimating and incident to the 4f system; the 4f system is used for performing beam combination on orthogonal circularly polarized light to generate a vector light field, and comprises a spatial light modulator capable of performing pure phase modulation on the light field, a first Fourier lens, a second Fourier lens, a double-hole filter, a doublet # imgabs0 # wave plate and a Ronchi grating. The SHG mode output of the vector light field with a complex structure can be dynamically regulated and controlled, and the method is simple and efficient; the device is simple in structure and high in flexibility, can generate a high-resolution vector light field in any polarization state by regulating and controlling the topological charge and the initial phase, can generate a high-resolution vortex light field in different polarization states, and is stable in structure.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a composite structure vector vortex light field control system based on the second harmonic of a BBO crystal. Background Art

[0002] The advent of laser technology marked a paradigm shift in nonlinear optics research. The first major advance in this field can be traced back to the first experimental verification of second harmonic generation, followed by the realization of third harmonic generation and second harmonic generation with spin angular momentum (SAM) characteristics. This close connection stems from the inherent characteristics of nonlinear optical effects: their weak interaction characteristics place stringent requirements on observation conditions, and effective excitation requires the use of high-power coherent light sources. In recent years, with the iterative upgrades of high-power laser devices and breakthroughs in new nonlinear materials, the related technical bottlenecks have been significantly improved. This technological innovation has directly driven a fundamental shift in the research paradigm. The research focus has gradually shifted from the early focus on quantitative process improvements such as improving energy conversion efficiency to the exploration of essential laws such as light field manipulation and characterization. Since then, the study of complex structured light has become a hot topic in the nonlinear field. Structured light refers to the ability to create complex light fields in both classical and quantum domains by manipulating the spatial and temporal degrees of freedom of light. By combining degrees of freedom, exotic optical states in two, three, and even four dimensions have been realized, including optical knots, skyrmions, Möbius strips, spatiotemporal structured light, ray-wave hybrid fields, quantum-like classical light, and photonic wheels. Despite rapid progress, the origins of structured light can be traced back to Thomas Young's double-slit experiment—perhaps the earliest example of structured light. The essence of structured light lies in the superposition principle, where interference (not limited to intensity interference) produces the desired structure. Modern theories view structured light as a linear superposition, encompassing geometric representations ranging from OAM and total angular momentum to a unified framework of multiple degrees of freedom. For example, plane waves can embody structure: a single plane wave carries a phase gradient, two plane waves form intensity structure (as in Young's experiment), three plane waves can produce phase singularities, and multiple plane waves can generate Bessel beams. By combining other degrees of freedom, such as polarization, two plane waves can form exotic polarization structures, which, when focused, can also produce three-dimensional synthetic chiral light. This close connection between linear interference and structured light has led to the majority of research focusing on linear optical elements, with the nonlinear optical effects of structured light only then receiving attention.

[0003] Although a relatively systematic theoretical system of mode conversion has been established in the current field, there are still deficiencies in the efficient control of nonlinear conversion. Exploring this method is an urgent problem that needs to be solved. Summary of the Invention

[0004] In order to overcome the deficiencies in the above-mentioned prior art, the present invention provides a high-resolution arbitrarily controllable polarization state distribution vector light field generation system based on scattering focusing, which realizes dynamic control of the SHG mode output of the complex structure vector light field based on the second harmonic control of the initial phase angle of the vector light field and the azimuth angle of the nonlinear medium pre-polarizer.

[0005] In order to achieve the above objectives, the technical solution adopted by the present invention is as follows: a composite structure vector vortex light field control system based on the second harmonic of BBO crystal, comprising:

[0006] A laser, used for emitting laser light and injecting it into a beam expanding lens;

[0007] A first collimating lens, used for collimating and incident on the 4f system;

[0008] The 4f system is used to combine orthogonal circularly polarized light beams to generate a vector light field, comprising a spatial light modulator capable of performing pure phase modulation on the light field, a first Fourier lens, a second Fourier lens, a double-aperture filter, a double-cemented Wave plate and a Ronchi grating; the order of arrangement is spatial light modulator, first Fourier lens, double hole filter, double cemented Wave plate, second Fourier lens, Ronchi grating, double-aperture filter close to double cemented Wave plate, the distance between each element is the focal length f of the Fourier lens; after the laser is incident on the spatial light modulator, the +1 order beams on the x-axis and y-axis of the spectrum are extracted through a double-hole filter, and the two beams are respectively made to pass through the double glue The different glued surfaces of the wave plate are converted into circularly polarized light with orthogonal left-handed and right-handed polarization directions, and finally the two beams are combined into a vector beam through a Ronchi grating;

[0009] Polarizer, used to control the incident light field and the generated second harmonic light field;

[0010] Nonlinear media, used to make the light field produce nonlinear effects;

[0011] The focusing lens and the second collimating lens focus the light beam on the nonlinear crystal through weak focusing control, and can also increase the intensity of the pump light source incident on the nonlinear crystal, thereby improving the quality of the second harmonic light field. The second collimating lens (8) collimates the light field to obtain higher imaging quality;

[0012] Multi-stage dichroic mirror to eliminate residual fundamental frequency components;

[0013] The CCD receiver is used to receive the generated second harmonic light field;

[0014] Among them, using phase modulation based on 4f system 4, the generated vector light field is shown in the following formula 1:

[0015]

[0016] in is the unit basis vector in the horizontal x direction in the Cartesian coordinate system (x,y), is the unit basis vector in the vertical y direction; represents the azimuth in the polar coordinate system, represents the polar radius, m is the topological charge, l is the radial variation parameter, r a is the light field radius, is the initial phase; the vector light field is mainly composed of the topological charge number m, the radial variation parameter l initial phase That is, by controlling parameters such as the topological charge and the initial phase, the vector light field of the corresponding polarization state can be obtained.

[0017] Furthermore, the vector light field obtained by coherent superposition of two circularly polarized lights with orthogonal left-handed and right-handed polarization directions passes through the polarizer, and its light field expression is shown in the following formula 2:

[0018]

[0019] Furthermore, the vector light beam is focused on the nonlinear medium after passing through the polarizer and focusing lens, and then is transmitted to the CCD receiver after the residual fundamental frequency component is eliminated by the dichroic mirror, thereby obtaining the second harmonic light field.

[0020] Furthermore, by changing the initial phase angle of the vector light field and the azimuth angle of the nonlinear medium pre-polarizer, the SHG light field mode of the polarization state space-varying vector light field can be flexibly controlled. The expression of the second harmonic light field is shown in the following formula 3:

[0021]

[0022] in is the unit basis vector in the horizontal x direction in the Cartesian coordinate system (x,y), is the unit basis vector in the vertical y direction; represents the azimuth in the polar coordinate system, represents the polar radius, m is the topological charge, l is the radial variation parameter, r a is the light field radius, is the initial phase. By changing the initial phase angle of the vector light field and the azimuth angle of the nonlinear medium pre-polarizer, the target second harmonic light field can be generated.

[0023] Furthermore, the nonlinear medium is barium metaborate crystal.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) It can dynamically control the SHG mode output of complex structure vector light field, which is simple and efficient.

[0026] (2) It has high flexibility and can generate high-resolution vector light fields of arbitrary polarization states by regulating the topological charge and initial phase. It can also generate vortex light fields of different polarization states with high resolution, and the structure is stable.

[0027] (3) It is suitable for fields that require the generation of high-resolution controllable light fields after nonlinear effects, and has the characteristics of convenient operation, flexible control, and stable effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the present invention;

[0029] Figure 2 It is the intensity distribution diagram of the local linear polarization vector fundamental frequency light field and its second harmonic light field with spatial variation of polarization state as φ0 changes;

[0030] Figure 3 It is the intensity distribution diagram of the vector fundamental frequency light field and its second harmonic light field with spatial variation of polarization state as δ changes.

[0031] Figure: 1, laser; 2, beam expander lens; 3, first collimator lens; 4, 4f system; 401, spatial light modulator; 402, first Fourier lens; 403, second Fourier lens; 404, double-aperture filter; 405, double cemented Wave plate; 406, Ronchi grating; 5, polarizer; 6, nonlinear medium; 7, focusing lens; 8, second collimating lens; 9, dichroic mirror; 10, CCD receiver. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] like Figure 1-Figure 3As shown, the technical solution adopted by the present invention is as follows: This embodiment provides a high-resolution arbitrarily controllable polarization state distribution vector light field generation system for scattering and focusing, including a 4f system 4 for generating a vector light field, a polarizer 5, a focusing lens 7, a nonlinear medium (BBO crystal) 6, a first collimating lens 3, a second collimating lens 8, a dichroic mirror 9 and a CCD receiver 10, wherein the 4f system 4 includes a spatial light modulator 401 capable of pure phase modulation, a first Fourier lens 402, a second Fourier lens 403, a double-aperture filter 404, and a double-cemented Wave plate 405 and a Ronchi grating 406 .

[0034] The nonlinear medium (BBO crystal) 6 is used to allow the vector light beam to pass through to generate the second harmonic, and is preferably made of barium borate crystal (BBO). The focusing lens 7 and the second collimating lens 8 focus the light beam on the nonlinear crystal through weak focusing control (the focal spot radius is 0.5mm). At the same time, it can also increase the intensity of the pump light source incident on the nonlinear crystal, thereby improving the quality of the second harmonic light field. The second collimating lens 8 collimates the light field to obtain higher imaging quality. The multi-stage dichroic mirror 9 is used to eliminate the residual fundamental frequency component. The CCD receiver 10 is used to receive the generated second harmonic light field;

[0035] Further, such as Figure 1 As shown, the 4f system 4 is used to combine orthogonal circularly polarized light beams to generate a vector light field, including a spatial light modulator 401 capable of performing pure phase modulation on the light field, a first Fourier lens 402, a second Fourier lens 403, a double-aperture filter 404, and a double-cemented Wave plate 405 and a Ronchi grating 406; the order of arrangement is spatial light modulator 401, first Fourier lens 402, double hole filter 404, double cemented Wave plate 405, second Fourier lens 403, Ronchi grating 406, double-aperture filter 404 are glued together Wave plate 405, except for the distance between each element is the focal length f of the Fourier lens. After the laser is incident on the spatial light modulator 401, it is extracted through the double-hole filter 404 on the x-axis and y-axis of the spectrum, and the two beams are respectively made to pass through the double glue The different glued surfaces of the wave plate 405 are converted into circularly polarized light with orthogonal left-handed and right-handed polarization directions, and finally the two beams are combined into a vector beam through the Ronchi grating 406; the input light field with different polarization and phase distribution depends on the hologram loaded on the spatial light modulator.

[0036] Furthermore, the vector light field obtained by coherent superposition of two circularly polarized lights with orthogonal left-handed and right-handed polarization directions passes through the polarizer 5, and its light field expression is shown in the following formula 2:

[0037]

[0038] Furthermore, the vector light beam passes through the polarizer 5 and the focusing lens 7 and is focused on the nonlinear medium 6. Then, after the residual fundamental frequency component is eliminated by the dichroic mirror 9, it is transmitted to the CCD receiver 10 to obtain the second harmonic light field.

[0039] Furthermore, by changing the initial phase angle of the vector light field and the azimuth angle of the pre-polarizer 5 of the nonlinear medium 6, the flexible control of the SHG light field mode of the polarization state space-varying vector light field is achieved. The expression of the second harmonic light field is shown in the following formula 3:

[0040]

[0041] The symbols have the same meaning as in Formula 1. By changing the initial phase angle of the vector light field and the azimuth angle of the nonlinear medium pre-polarizer, the target second harmonic light field can be generated.

[0042] Furthermore, this method can dynamically control the SHG mode output of complex structure vector light fields in a simple and efficient manner.

[0043] Specifically, the light source is a laser with a wavelength of 800nm, and a type II phase-matched BBO crystal is used as the nonlinear medium. The results show that when the incident light field configuration is changed, the SHG mode output conversion mechanism based on the regulation of orthogonal polarization components remains stable. This method provides a new method and approach for the nonlinear manipulation of complex structured light fields.

[0044] Figure 2 The intensity distribution diagram of the local linear polarization vector fundamental frequency light field and its second harmonic light field with the change of polarization state space is described, which shows the effectiveness of this method. The intensity distribution diagram of the local linear polarization vector fundamental frequency light field and its second harmonic light field with the change of polarization state space is shown. The leftmost column (I) in the figure is the polarization state distribution diagram of the vector light field. The second largest column is the fundamental frequency light field E x Quantity and E y The cross-sectional light intensity I corresponding to the component x and I y The third column (III) is the intensity distribution diagram of the corresponding second harmonic light field, and the fourth column (Experiment) is the experimental results. The size of each small figure is 3500λ×3500λ;

[0045] Figure 3 The intensity distribution diagram of the vector fundamental frequency light field and its second harmonic light field with spatially varying polarization states as δ varies is described, demonstrating the effectiveness of this method. The intensity distribution diagram of the vector fundamental frequency light field and its second harmonic light field with spatially varying polarization states as δ varies. The leftmost column (I) in the figure is the polarization state distribution diagram of the vector light field. The second largest column is the fundamental frequency light field Ex Quantity and E y The cross-sectional light intensity I corresponding to the component x and I y The third column (III) shows the intensity distribution of the corresponding second harmonic light field, and the fourth column (Experiment) shows the experimental results. The size of each small figure is 3500λ×3500λ.

[0046] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite structure vector vortex light field control system based on the second harmonic of BBO crystal, characterized by: include: A laser (1) for emitting laser light and incident on a beam expanding lens (2); a first collimating lens (3) for collimating and incident on the 4f system (4); The 4f system (4) is used to combine orthogonal circularly polarized light beams to generate a vector light field, and comprises a spatial light modulator (401) capable of performing pure phase modulation on the light field, a first Fourier lens (402), a second Fourier lens (403), a double-aperture filter (404), a double-cemented a wave plate (405) and a Ronchi grating (406); The order of arrangement is spatial light modulator (401), first Fourier lens (402), double hole filter (404), double glued Wave plate (405), second Fourier lens (403), Ronchi grating (406), double hole filter (404) are glued together Wave plate (405), the distance between all other components is the focal length f of the Fourier lens; after the laser is incident on the spatial light modulator (401), the +1 order beams on the x-axis and y-axis of the spectrum are extracted through the double-hole filter (404), and the two beams are respectively made to pass through the double glue Different glued surfaces of the wave plate (405) are converted into circularly polarized light with orthogonal left-handed and right-handed polarization directions, and finally the two beams are combined into a vector beam through a Ronchi grating (406); A polarizer (5) for regulating the incident light field and the generated second harmonic light field; Nonlinear medium (6), used to make the light field produce nonlinear effects; A focusing lens (7) and a second collimating lens (8), wherein the focusing lens (7) focuses the light beam on the nonlinear crystal through weak focusing control, and can also increase the intensity of the pump light source incident on the nonlinear crystal, thereby improving the quality of the second harmonic light field, and the second collimating lens (8) collimates the light field to obtain higher imaging quality; A multi-stage dichroic mirror (9) for eliminating the residual fundamental frequency component; The CCD receiver (10) is used to receive the generated second harmonic light field; Among them, using phase modulation based on 4f system 4, the generated vector light field is shown in the following formula 1: in is the unit basis vector in the horizontal x direction in the Cartesian coordinate system (x,y), is the unit basis vector in the vertical y direction; represents the azimuth in the polar coordinate system, represents the polar radius, m is the topological charge, l is the radial variation parameter, r a is the light field radius, is the initial phase; the vector light field is mainly composed of the topological charge number m, the radial variation parameter l initial phase That is, by controlling parameters such as the topological charge and the initial phase, the vector light field of the corresponding polarization state can be obtained.

2. The composite structure vector vortex light field control system based on the second harmonic of BBO crystal according to claim 1 is characterized by: The vector light field obtained by coherent superposition of two circularly polarized lights with orthogonal left-handed and right-handed polarization directions passes through the polarizer (5), and its light field expression is shown in the following formula 2:

3. The composite structure vector vortex light field control system based on the second harmonic of BBO crystal according to claim 2 is characterized in that: The vector light beam passes through the polarizer (5) and the focusing lens (7) and is focused on the nonlinear medium (6). The vector light beam is then passed through the dichroic mirror (9) to eliminate the residual fundamental frequency component and is then transmitted to the CCD receiver (10), thereby obtaining a second harmonic light field.

4. The composite structure vector vortex light field control system based on the second harmonic of BBO crystal according to claim 3 is characterized by: By changing the initial phase angle of the vector light field and the azimuth angle of the polarizer (5) in front of the nonlinear medium (6), the SHG light field mode of the polarization state space-varying vector light field can be flexibly controlled. The expression of the second harmonic light field is shown in the following formula 3: in is the unit basis vector in the horizontal x direction in the Cartesian coordinate system (x,y), is the unit basis vector in the vertical y direction; represents the azimuth in the polar coordinate system, represents the polar radius, m is the topological charge, l is the radial variation parameter, r a is the light field radius, The initial phase is changed, and the target second harmonic light field can be generated by changing the initial phase angle of the vector light field and the azimuth angle of the polarizer (5) in front of the nonlinear medium (6).

5. The composite structure vector vortex light field control system based on the second harmonic of BBO crystal according to claim 1 is characterized in that: The nonlinear medium (6) is barium metaborate crystal.

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