CN211318937U - Vector beam-based nonlinear frequency conversion device - Google Patents
Vector beam-based nonlinear frequency conversion device Download PDFInfo
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- CN211318937U CN211318937U CN201922286474.8U CN201922286474U CN211318937U CN 211318937 U CN211318937 U CN 211318937U CN 201922286474 U CN201922286474 U CN 201922286474U CN 211318937 U CN211318937 U CN 211318937U
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Abstract
A non-linear frequency conversion device based on vector beams comprises a light processing component, a light source and a light source, wherein the light processing component is used for processing seed light into circularly polarized light; the angular momentum module is used for increasing orbital angular momentum of input circularly polarized light and then outputting light beams with polarization and orbital angular momentum superposition states; and the nonlinear frequency conversion module is used for performing nonlinear frequency conversion on the input light beam and then outputting the light beam after the nonlinear frequency conversion. The utility model discloses can realize the operation and the nonlinear frequency conversion of vector light beam, can be used for the usable frequency range of widen light beam, it has very strong validity and robustness, has used less optical element moreover, adjusts in a flexible way, has very strong application prospect. The device can realize the frequency doubling operation of the vector light beam, is also suitable for other second-order nonlinear processes, such as sum frequency and difference frequency conversion processes, and can be popularized to the quantum state of a single photon.
Description
Technical Field
The utility model relates to a laser technology, nonlinear optics physics technical field and atomic physics technical field especially relate to a nonlinear frequency conversion device based on vector light beam.
Background
Since the advent of laser, the development of laser technology over the past few decades has focused on spatially uniform polarization states. Laser beams with spatially non-uniform polarization states (e.g., vector beams) have received increasing attention in recent years. The vector light beam has special light intensity and polarization distribution, and can be applied to a plurality of fields of large numerical aperture focusing, optical capturing, laser processing, optical cages, super-resolution imaging, high-capacity communication, quantum information science and the like.
As an important laser technology, nonlinear frequency conversion has also been studied. Nonlinear frequency conversion provides an important method to extend the usable frequency range of the light beam when it is difficult for them to directly produce light beams in the appropriate frequency band.
To date, manipulation and nonlinear frequency conversion of vector beams has remained very challenging because of the polarization sensitivity of most nonlinear processes.
SUMMERY OF THE UTILITY MODEL
In order to solve how to use the technique of nonlinear frequency conversion to the laser beam that realizes inhomogeneous polarization state, for this reason, the utility model provides a nonlinear frequency conversion device based on vector light beam. The utility model adopts the following technical scheme:
a non-linear frequency conversion device based on vector beams comprises
The light treatment component is used for treating the seed light into circularly polarized light;
the angular momentum module is used for increasing orbital angular momentum of input circularly polarized light and then outputting light beams with polarization and orbital angular momentum superposition states;
and the nonlinear frequency conversion module is used for performing nonlinear frequency conversion on the input light beam and then outputting the light beam after the nonlinear frequency conversion.
A first scheme of the nonlinear frequency conversion module, wherein the nonlinear frequency conversion module comprises a first dichroic mirror, a third polarizing beam splitter, a first dichroic half-wave plate, a first crystal, a first parabolic reflector and a second parabolic reflector, and the first parabolic reflector and the second parabolic reflector are symmetrically arranged on two sides of the first crystal; the input light beam enters a third polarization spectroscope after passing through a first dichroic mirror, the horizontal polarized light and the vertical polarized light are split by the third polarization spectroscope, and the horizontal polarized light sequentially passes through a first bicolor half-wave plate, a first polished surface reflector, a first crystal, a second polished surface reflector and the third polarization spectroscope; the vertical polarized light sequentially passes through the second polished surface reflector, the first crystal, the first polished surface reflector, the first dichroic half-wave plate and the third polarizing beam splitter, and the horizontal polarized light and the vertical polarized light are output by the third polarizing beam splitter and then are converged to form a beam with nonlinear frequency conversion.
A second solution of the nonlinear frequency conversion module, the nonlinear frequency conversion module comprises a first focusing lens, a second dichroic mirror, a fourth dichroic polarizing beam splitter, a second dichroic half-wave plate, a seventh reflecting mirror, a second crystal, an eighth reflecting mirror, a first collimating lens, the input light beam passes through the first focusing lens and the second dichroic mirror in sequence, the fourth bicolor polarization beam splitter is divided into horizontal polarized light and vertical polarized light, the horizontal polarized light sequentially passes through the second bicolor half-wave plate, the seventh reflector, the second crystal, the eighth reflector and the fourth bicolor polarization beam splitter and then is output as a first path, the vertical polarized light sequentially passes through the eighth reflector, the second crystal, the seventh reflector, the second bicolor half-wave plate and the fourth bicolor polarization beam splitter and then is output as a second path, and the first path output and the second path output are mixed and then pass through the first collimating lens and then are output as a nonlinear frequency conversion module.
In a third aspect of the nonlinear frequency conversion module, the nonlinear frequency conversion module includes a second focusing lens, a third crystal group, a second collimating lens, and an optical filter, which are sequentially disposed.
Specifically, the crystal is a periodically polarized KTP crystal, and the vertically polarized light and the horizontally polarized light are respectively focused on the center of the crystal from two opposite directions of the crystal.
Limiting an angular momentum module, wherein the angular momentum module comprises a second polarizing beam splitter, a second reflecting mirror, a third reflecting mirror, a vortex phase plate and a fourth reflecting mirror, a light beam input into the angular momentum module is divided into horizontal polarized light and vertical polarized light by the second polarizing beam splitter, and the horizontal polarized light sequentially passes through the second reflecting mirror, the third reflecting mirror, the vortex phase plate and the fourth reflecting mirror and then is output by the second polarizing beam splitter; the vertically polarized light sequentially passes through the fourth reflector, the vortex phase plate, the third reflector and the second reflector, then is output by the second polarizing beam splitter, and two paths of light beams output by the second polarizing beam splitter are mixed and then serve as output light beams of the angular momentum module.
The first measurement module comprises a third quarter wave plate, a fifth reflector, a fourth quarter wave plate, a sixth reflector and a first CCD element, the third quarter wave plate, the fifth reflector and the fourth quarter wave plate are sequentially arranged on a light path between the angular momentum module and the nonlinear frequency conversion module, and light reflected by the fifth reflector is reflected to the first CCD element through the sixth reflector.
And the output end of the nonlinear frequency conversion module is also provided with a second measurement module, and the second measurement module comprises a fifth-fourth wave plate and a second CCD element which are arranged on an output optical path of the nonlinear frequency conversion module.
And defining a light processing assembly, wherein the light processing assembly comprises a circularly polarized light acquisition module, and the circularly polarized light acquisition module comprises a second half-wave plate and a second quarter-wave plate which are arranged in sequence.
The light processing assembly is further limited, the light processing assembly further comprises a light generation module and a light adjusting module which are sequentially arranged at the front end of the circularly polarized light acquisition module, and the light adjusting module comprises a first half wave plate, a first quarter wave plate and a first polarization spectroscope which are sequentially arranged along a light path.
The utility model has the advantages that:
(1) the utility model discloses can realize the operation and the nonlinear frequency conversion of vector light beam, can be used for the usable frequency range of widen light beam, it has very strong validity and robustness, has used less optical element moreover, adjusts in a flexible way, has very strong application prospect. The device can realize the frequency doubling operation of the vector light beam, is also suitable for other second-order nonlinear processes, such as sum frequency and difference frequency conversion processes, and can be popularized to the quantum state of a single photon.
(2) The nonlinear frequency conversion module is capable of frequency doubling the vector beam, but requires that the pumped vector beam is first converted into an exponential form of the mixed polarization vector beam by the angular momentum module. The device can obtain vector beams with any polarization distribution by operating and carrying out nonlinear frequency conversion on the vector beams with different topological charges.
(3) The application discloses three schemes of nonlinear frequency conversion modules, which can realize the function of nonlinear frequency conversion.
(4) The angular momentum module adds orbital angular momentum to the input circularly polarized light beam and then outputs the light beam with the superposition state of polarization and orbital angular momentum.
(5) And the second measuring module detects and records the light beam after nonlinear frequency conversion.
(6) The first measuring module is used for ensuring that the light beam input by the nonlinear frequency conversion module meets the requirement, and when the requirement is not met, the relevant parameters of the light processing component and the angular momentum module can be adjusted.
(7) The light processing assembly is used for linearly polarizing the light generated by the light generation module, wherein the light adjusting module is used for controlling the intensity and the polarization angle of the linearly polarized light and converting the light beam from the linearly polarized light to circularly polarized light.
Drawings
Fig. 1 is a modular connection diagram of the present invention.
Fig. 2 is a structural view of a light generating module.
Fig. 3 is a structural diagram of a light adjusting module.
Fig. 4 is a structural diagram of a circularly polarized light acquisition module.
Fig. 5 is a structural view of an angular momentum module.
Fig. 6 is a structural diagram of a first detection module.
Fig. 7 is a block diagram of a first aspect of a non-linear frequency conversion module.
Fig. 8 is a block diagram of a second aspect of a non-linear frequency conversion module.
Fig. 9 is a block diagram of a third aspect of a non-linear frequency conversion module.
Fig. 10 is a structural diagram of a second detection module.
The notations in the figures have the following meanings:
1-light treatment Assembly
111-semiconductor laser 112-first half wave plate 113-first quarter wave plate
12-first polarizing beam splitter 13-first mirror
141-second half-wave plate 142-second quarter-wave plate
2-angular momentum module 21-second polarizing beamsplitter 22-second reflecting mirror 23-third reflecting mirror
24-vortex phase plate 25-fourth mirror
3-first measuring module 31-third quarter wave plate 32-fifth mirror
33-fourth quarter-wave plate 34-sixth mirror 35-first horizontal polarizer
36-first CCD element
4-nonlinear frequency conversion module 411-first dichroic mirror 412-third polarization beam splitter
413-first dichroic half-wave plate 414-first polished face mirror 415-first crystal
416-second polished surface mirror
421-first focusing lens 422-second dichroic mirror 423-fourth dichroic polarizing beamsplitter
424-second dichroic half-wave plate 425-seventh mirror 426-second crystal
427-eighth mirror 428-first collimating lens
431-second focusing lens 432-third lens group 433-second collimating lens
434-optical filter
5-second measuring module 51-ninth mirror 52-fifth quarter wave plate
53-second horizontal polarizer 54-second CCD element
Detailed Description
As shown in FIG. 1, a non-linear frequency conversion device based on vector beams comprises
A light processing component 1 for processing the seed light into circularly polarized light;
an angular momentum module 2 for increasing orbital angular momentum of the input circularly polarized light and then outputting a light beam having a superimposed state of polarization and orbital angular momentum
And the nonlinear frequency conversion module 4 is used for performing nonlinear frequency conversion on the input light beam and then outputting the nonlinear frequency-converted light beam.
A first measuring module 3 arranged between the angular momentum module 2 and the nonlinear frequency conversion module 4 for measuring the light beam output from the angular momentum module 2
Detecting and recording, if the monitoring result can not meet the requirement of the subsequent optical path system, adjusting the relevant parameters of the optical processing component 1 to make the light beam
The requirements of a subsequent optical path system can be met;
and the second measuring module 5 is arranged at the output end of the nonlinear frequency conversion module 4 and is used for detecting and recording the light beam after nonlinear frequency conversion.
The modules are described in detail below:
specifically, the light processing assembly 1 includes a light generation module, a light adjustment module, and a circularly polarized light acquisition module, which are sequentially disposed. The specific description is as follows:
11. light generating module
As shown in fig. 2, the light generating module includes a semiconductor laser 111, and the semiconductor laser 111 is a continuous laser amplified by a semiconductor seed light via an optical fiber amplifier, which provides an initial beam for the whole system. The center wavelength of the seed light is 1560nm, the line width is less than 10MHz, the output power after passing through the amplifier is more than 1W, and the line width is less than 100MHz.
12. Light adjusting module
As shown in fig. 3, the light adjusting module includes a first half-wave plate 112, a first quarter-wave plate 113, and a first polarization beam splitter 12, which are sequentially disposed along the light path. Wherein the first half-wave plate 112 and the first quarter-wave plate 113 work together to control and adjust the intensity of the input laser with the working wavelength of 1560nm, the first polarization beam splitter 12 is used to obtain the horizontal polarization beam
The first polarization beam splitter 12 reflects and refracts light for a plurality of times, the vertically polarized light split by the first polarization beam splitter 12 is emitted in the vertical direction, and the split horizontally polarized light is formed by transmitting in the horizontal direction
It can be expressed by the following formula:
in this embodiment the first mirror 13 will polarize the light horizontally
The light is reflected to enter a circularly polarized light acquisition module, the coating parameter of a first reflector 13 is HR @1560nm, and the incidence is 45 degrees。
13. Circularly polarized light acquisition module
As shown in fig. 4, the circular polarization acquiring module includes a second half-wave plate 141 and a second quarter-wave plate 142, which are sequentially disposed. The working wavelength of the second half-wave plate 141 is 1560nm, and the fast axis and the horizontal polarized light of the second half-wave plate are set
The included angle of polarization direction is α, and different α value can be obtained by rotating and adjusting the second half-wave plate 141, and the effect on the light beam can be expressed by the following formula:
the second quarter-wave plate 142 has a working wavelength of 1560nm, and is provided with its fast axis and horizontal polarized light
The polarization direction has an angle of-pi/4, which can convert the polarized light emitted from the second half-wave plate 141 into circularly polarized light. Its effect on the beam can be expressed by the following equation:
2. angular momentum module 2
As shown in fig. 5, the angular momentum module 2 includes a second pbs 21, a second reflecting mirror 22, a third reflecting mirror 23, a vortex phase plate 24, and a fourth reflecting mirror 25, wherein the second pbs 21 is coated with AR @1560nm, 0 ° incident light, and is used for separating circularly polarized light into horizontally polarized light and vertically polarized light, wherein the horizontally polarized light is transmitted along the original optical path propagation direction and then reflected into the vortex phase plate 24 by the second reflecting mirror 22 and the third reflecting mirror 23. The vertically polarized light is 90 degrees folded from the original light path and reflected to the vortex phase plate 24 by the fourth mirror 25.
The working wavelength of the vortex phase plate 24 is 1560nm, and light beams passing through the vortex phase plate 24 will be transmittedAdding orbital angular momentum to horizontally polarized light
Vertically polarized light is added with orbital angular momentum
The horizontally polarized light added with the upper-track angular momentum is reflected back to the second polarizing beam splitter 21 via the fourth mirror 25 and transmitted from the second polarizing beam splitter 21. The vertically polarized light added with the upper orbital angular momentum is reflected back to the second pbs 21 via the third reflecting mirror 23 and the second reflecting mirror 22, and is 90-degree-folded in the second pbs 21 and then exits therefrom. It should be noted that the vortex phase plate 24 needs to be placed in the middle of the annular structure formed by all the components of the angular momentum module 2, specifically, between the third mirror 23 and the fourth mirror 25, so as to ensure that the optical field at the output end of the annular structure contains both the optical field and the optical field
And
the surfaces of the second reflector 22, the third reflector 23 and the fourth reflector 25 are all HR @1560nm coated films, and the functions of the HR @1560nm coated films are all used for deflecting the light path.
The horizontally polarized light added with the upper track angular momentum and the vertically polarized light added with the upper track angular momentum are emitted from the second polarization beam splitter 21 and then are superimposed to form a mixed light
The combined effect of the second PBS 21, the second reflector 22, the third reflector 23, the vortex phase plate 24 and the fourth reflector 25 on the light beam can be accurately expressed by the following matrix:
wherein, Delta1Is the phase difference in the loop formed by the specular reflection and the birefringence of the second polarizing beam splitter 21. l is the topological charge, which is an integer determined by the properties of the vortex phase plate 24.
Superimposed mixed light
The superposition mode, which includes the polarization and orbital angular momentum of the beam, can be expressed as:
3. first measuring module 3
As shown in fig. 6, the first measurement module 3 includes a third quarter wave plate 31, a fifth mirror 32, a fourth quarter wave plate 33, a sixth mirror 34, and a first CCD element 36, the third quarter wave plate 31, the fifth mirror 32, and the fourth quarter wave plate 33 are sequentially disposed on the optical path between the angular momentum module 2 and the nonlinear frequency conversion module 4, and the light reflected by the fifth mirror 32 is reflected to the first CCD element 36 via the sixth mirror 34.
The working wavelength 1560nm of the third quarter-wave plate 31 is set to have an included angle of pi/4 between the fast axis and the polarization direction of the horizontally polarized light, and the effect on the light beam is expressed by the following formula:
superimposed mixed light
Reaches the third quarter-wave plate 31, and becomes linearly polarized light with orbital angular momentum
And then is deflected by the fifth mirror 32 and the sixth mirror 34 to reach the first CCD element 36. Wherein
Can be represented by the following formula:
wherein θ is 2(α + Δ)1/4)。
The first CCD element 36, which has an operating band of 1.5 μm, will record first the state 1 of the beam and then the state 2 of the beam after placing the first horizontal polarizer 35 in front of the first CCD element 36, the states 1 and 2 reflecting the beam before the non-linear frequency conversion
The characteristic of (c). The first horizontal polarizer 35 has an operating wavelength of 1560nm.
The surfaces of the fifth reflector 32 and the sixth reflector 34 are coated with films HR @1560nm, the incident angle is 45 degrees, and the functions of the fifth reflector and the sixth reflector are used for deflecting the light path. After the first CCD element 36 has recorded state 1 and state 2, the fifth mirror 32 will be removed, after which,
as a pump beam into the nonlinear frequency conversion process.
The working wavelength of the fourth quarter-wave plate is 1560nm, the included angle between the fast axis of the fourth quarter-wave plate and the polarization direction of the horizontal polarized light is-pi/4, and the fourth quarter-wave plate has the function of pumping light beams
Is reduced to
If the monitoring result (status 1 and status 2 of the light beam) can not satisfy the requirement of the subsequent optical path system, the relevant parameters of the optical processing component 1 can be adjusted to enable the light beam
Can meet the requirements of a subsequent optical path system, and then the angle of the light beam is changedAnd the momentum module 2.
4.1. First scheme of nonlinear frequency conversion module 4
As shown in fig. 7, the nonlinear frequency conversion module 4 includes a first dichroic mirror 411, a third polarizing beam splitter 412, a first dichroic half-wave plate 413, a first crystal 415, and a first parabolic mirror and a second parabolic mirror 416 symmetrically disposed on both sides of the first crystal 415; the input light beam enters the third polarization beam splitter 412 after passing through the first dichroic mirror 411, and the horizontal polarized light and the vertical polarized light split by the third polarization beam splitter 412 pass through the first dichroic half-wave plate 413, the first polished surface reflecting mirror 414, the first crystal 415, the second polished surface reflecting mirror 416, and the third polarization beam splitter 412 in sequence; the vertically polarized light sequentially passes through the second polished surface reflector 416, the first crystal 415, the first polished surface reflector 414, the first dichroic half-wave plate 413 and the third polarizing beam splitter 412, and the horizontally polarized light and the vertically polarized light are output by the third polarizing beam splitter 412 and then are converged to form a beam with nonlinear frequency conversion.
The first dichroic mirror 411 is coated with AR @1560nm on the incident surface corresponding to the light beam of the nonlinear frequency conversion module 4, and coated with AR @1560nm, HR @780nm and an incident angle of 45 DEG on the emergent surface, and has the function of reducing the reduced light beam
Can be smoothly transmitted therethrough. And the frequency doubling light beam after the nonlinear frequency conversion reaches the surface of the frequency doubling light beam, generates light path deflection and is output from the nonlinear frequency conversion module 4.
The third PBS 412 has a surface coated with AR @1560nm, AR @780nm and an incident angle of 0 DEG, and has the function of reducing
The light is divided into horizontally polarized light and vertically polarized light, the horizontally polarized light is transmitted out from the horizontal direction, and the vertically polarized light is refracted and emitted out at 90 degrees. The other function is to transmit the frequency-doubled horizontal polarized light from the horizontal direction, the frequency-doubled vertical polarized light is reflected by 90 degrees, and the two are combined after being reflectedAnd forming mixed light after frequency multiplication.
The lambda/2 of the first dichroic half-wave plate 413 is @1560nm &780nm, the fast axis of the first dichroic half-wave plate is arranged to form an included angle pi/4 with the polarization direction of horizontal polarized light, and the first dichroic half-wave plate has the functions of: the pumped horizontally polarized light is converted to vertically polarized light. The second function is as follows: and converting the frequency-doubled vertical polarized light into horizontal polarized light.
The first polished surface mirror 414 has a dimension of 1 inch, an off-axis angle of 45 degrees, and a focal length of 101.6mm, and the silver plating film functions to focus the pump beam at the center of the first crystal 415. It is worth particularly stating that: the above parameters are applicable to this embodiment, and in other similar embodiments, these parameters are adapted and adjusted, but all fall within the scope of the present invention.
The first crystal 415 is a periodically polarized KTP crystal, specifically a PPKTP, Type-0(ZZZ) Type phase matching, the geometric dimension is 1mm × 2mm × 8mm, the polarization period is 25.01 μm, the phase matching temperature is 45 ℃, the first crystal is sensitive to vertical polarized light only, and after the first crystal acts on the vertical polarized light, the relationship between the generated frequency doubling light beam and the pump light beam can be expressed by the following formula:
E2ω∝(Eω)2
above, the comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:
wherein, Delta2Is the phase difference in the above nonlinear frequency conversion module 4 mainly caused by the asymmetry of the first crystal 415.
Taking the frequency doubling effect of the first crystal 415 into account, the overall process can be approximated by the following equation:
E2ω∝T(Eω)2
the generated frequency-doubled light beams are combined by the third pbs 412, reflected by the first dichroic mirror 411, and output from the nonlinear frequency conversion module 4.
4.2. Second scheme of nonlinear frequency conversion module 4
As shown in fig. 8, the nonlinear frequency conversion module 4 includes a first focusing lens 421, a second dichroic mirror 422, a fourth dichroic polarizing beam splitter 423, a second dichroic half-wave plate 424, a seventh reflecting mirror 425, a second crystal 426, an eighth reflecting mirror 427, a first collimating lens 428, the input light beam passes through the first focusing lens 421 and the second dichroic mirror 422 in sequence, the fourth dichroic polarizing beam splitter 423 is then divided into a horizontal polarized light and a vertical polarized light, the horizontal polarized light sequentially passes through the second dichroic half-wave plate 424, the seventh reflecting mirror 425, the second crystal 426, the eighth reflecting mirror 427, and the fourth dichroic polarizing beam splitter 423 and then is outputted as a first path, the vertical polarized light sequentially passes through the eighth reflecting mirror 427, the second crystal 426, the seventh reflecting mirror 425, the second dichroic half-wave plate 424, and the fourth dichroic polarizing beam splitter 423 and then is outputted as a second path, and the first path output and the second path output are mixed and then are outputted as the output of the nonlinear frequency conversion module 4 after passing through the first collimating lens 428.
The first focusing lens 421 has a surface coating AR @1560nm and a focal length f1@1560nm, which functions to focus the incident beam at the center of the second crystal 426.
The second dichroic mirror 422 is coated with AR @1560nm on the incident surface corresponding to the light beam entering the nonlinear frequency conversion module 4, coated with AR @1560nm and HR @780nm on the emergent surface, the incident angle is 45 degrees, and the first function is reduced
Can be smoothly transmitted therethrough. And the nonlinear frequency-converted frequency-doubled light beam reaches the surface of the nonlinear frequency-converted frequency-doubled light beam and then undergoes optical path deflection to enter the first collimating lens 428.
The fourth bicolor polarizing beam splitter 423 is coated with AR @1560nm and AR @780nm on the surface, the incident angle is 0 degree, and the function is that the reduced product is reduced
The light is divided into horizontally polarized light and vertically polarized light, the horizontally polarized light is transmitted out from the horizontal direction, and the vertically polarized light is refracted by 90 DEG and emitted. The second function is to transmit the frequency-doubled horizontal polarized light from the horizontal direction, the frequency-doubled vertical polarized light is refracted and emitted at 90 degrees, and the two lights are emitted to synthesize the frequency-doubled mixed light.
The lambda/2 of the second dichroic half-wave plate 424 is @1560nm &780nm, the fast axis of the second dichroic half-wave plate is arranged to form an angle pi/4 with the polarization direction of the horizontally polarized light, and the second dichroic half-wave plate has the function of converting the pumped horizontally polarized light into vertically polarized light. The second function is to convert the frequency-doubled vertical polarized light into horizontal polarized light.
The surfaces of the seventh reflecting mirrors 425 are coated with films of HR @1560nm and HR @780nm, and the functions of the seventh reflecting mirrors are used for deflecting the light path.
The second crystal 426 be periodic polarization KTP crystal, concrete PPKTP, Type-0(ZZZ) Type position phase-match, the geometric dimension is 1mm × 2mm × 8mm, the polarization cycle is 25.01μm, the phase matching temperature is 45 ℃, the phase matching temperature is sensitive to vertical polarization light only, and after the phase matching temperature is influenced, the relationship between the generated frequency doubling light beam and the pump light beam can be expressed by the following formula:
E2ω∝(Eω)2
the surfaces of the eighth reflecting mirror 427 are all coated films with the wavelength of HR @1560nm and the wavelength of HR @780nm, and the functions of the eighth reflecting mirror 427 are all used for deflecting the light path.
The first focusing lens 421 has a surface coated with AR @780nm film and a focal length f2@780nm，f2＝f1The function of which is to collimate the converging light beam.
Above, the comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:
wherein, Delta2Is the phase difference in the above loop that is mainly caused by the asymmetry of the crystal.
Taking the frequency doubling effect of the second crystal 426 into account, the overall process can be approximated by the following equation:
E2ω∝T(Eω)2
the generated frequency-doubled light beams are combined by the fourth dichroic polarizing beam splitter 423, reflected by the second dichroic mirror 422, collimated by the first collimating lens 428, and output from the nonlinear frequency conversion module 4.
4.3. Third scheme of nonlinear frequency conversion module 4
As shown in fig. 9, the nonlinear frequency conversion module 4 includes a second focusing lens 431, a third crystal group 432, a second collimating lens 433, and a filter 434, which are sequentially disposed.
The second focusing lens 431 has a surface coated with AR @1560nm and a focal length f1@1560nm, which functions to focus the incident beam at the center of the third crystal group 432.
The third crystal group 432 is composed of two identical periodically polarized KTP crystals, the second periodically polarized KTP crystal is placed by rotating 90 degrees relative to the first periodically polarized KTP crystal, the included angle of the optical axes of the second periodically polarized KTP crystal and the first periodically polarized KTP crystal is 90 degrees, the two periodically polarized KTP crystals have the parameters of Type-0(ZZZ) Type position matching, the geometric dimension is 1mm × 2mm, × 8mm and the polarization period is 25.01μmThe phase matching temperature is 45 ℃, which is sensitive only to vertically polarized light. After the action, the relationship between the generated frequency doubling beam and the pump beam can be represented by the following formula:
E2ω∝T(Eω)2
the surface of the second collimating lens 433 is coated with AR @780nm, the focal length f2@780nm，f2＝f1The function of which is to collimate the converging light beam.
The surface of the optical filter 434 is coated with films HR @1560nm and AR @780nm, and the optical filter has the function of filtering light which is not subjected to nonlinear conversion and enabling light beams subjected to nonlinear conversion to pass through smoothly.
Above, the comprehensive effect of the nonlinear frequency conversion module 4 on the polarization state of the light beam can be expressed by the following formula:
wherein, Delta2Is mainly crystalline in the above loopPhase difference due to asymmetry.
Taking the frequency doubling effect of the third transistor set 432 into consideration, the overall process can be approximated by the following formula:
E2ω∝T(Eω)2
the generated frequency-doubled light beam is output from the nonlinear frequency conversion module 4 after passing through the second collimating lens 433 and the optical filter 434.
5. Second measuring module 5
As shown in fig. 10, the second measurement module 5 includes a ninth mirror 51, a fifth quarter wave plate 52, a second horizontal polarizer 53, and a second CCD element 54, which are disposed on the output optical path of the nonlinear frequency conversion module 4.
The ninth reflector 51 is coated with film HR @780nm at an incident angle of 45 DEG and functions to fold the light path and fold the frequency-doubled light beam to the fifth quarter wave plate 52.
The lambda/4 of the fifth quarter wave plate 52 is @780nm, and the fast axis of the fifth quarter wave plate is set to form an angle pi/4 with the polarization direction of the horizontally polarized light, and the effect on the light beam can be expressed as follows:
the frequency-doubled light beam after the fifth-fourth wave plate 52
To the second CCD element 54, which is connected with
By comparison, the frequency is doubled, which can be expressed as:
wherein Θ is 4 α + Δ1+Δ2/2-π/4
The working wavelength band of the second CCD element 54 is 780nm, and the working wavelength of the second horizontal polarizer 53 is 780nm, which functions to filter out light rays with other polarization directions and only to keep light rays with the polarization direction being the horizontal polarization direction to pass through.
The second CCD element 54 will record the frequency-doubled light beam
State 3, and then state 4 of the beam after placing a second horizontal polarizer 53 in front of the second CCD element 54, i.e. states 3 and 4 reflect the frequency doubled (non-linear frequency converted) beam
State 4 is the result of the horizontal polarization direction projection measurement.
At present, a bottleneck point of many current research situations is to directly apply the above
Direct frequency doubling, which cannot obtain ideal frequency doubling light speed, is theoretically analyzed as follows:
will be provided with
The theoretical expression for direct frequency doubling is as follows:
in the above equation, the constant term 1/2 represents a gaussian beam and the other term represents an orbital angular momentum beam superimposed by linear polarization, which is not a desirable result.
Through the utility model discloses the device, before carrying out the doubling of frequency to the vector light beam, can convert the vector light beam of pumping into the mixed polarization vector light beam of index form at first. The frequency-doubled light beam thus obtained is as described above
Shown in, it is and
in contrast to the above-mentioned results,
in addition to having a vector beam frequency doubling component (l → 2l), a gaussian mode with no topological charge,
is not ideal vector light beam, so that ideal frequency doubling vector light beam can be obtained by the device.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, and all modifications, equivalents, improvements and the like that are made within the spirit and principles of the present invention should be included in the scope of the present invention.
Claims (10)
1. A non-linear frequency conversion device based on vector beams is characterized by comprising
A light treatment assembly (1) for treating the seed light into circularly polarized light;
an angular momentum module (2) for increasing orbital angular momentum of the input circularly polarized light and then outputting a light beam having a state of superposition of polarization and orbital angular momentum
A non-linear frequency conversion module (4) for converting an input light beam
And performing nonlinear frequency conversion, and then outputting the nonlinear frequency-converted light beam.
2. The device for nonlinear frequency conversion based on vector beams according to claim 1, wherein the nonlinear frequency conversion module (4) comprises a first dichroic mirror (411), a third polarizing beam splitter (412), a first dichroic half-wave plate (413), a first crystal (415), a first parabolic mirror and a second parabolic mirror symmetrically arranged at two sides of the first crystal (415); an input light beam enters a third polarization beam splitter (412) after passing through a first dichroic mirror (411), horizontal polarized light and vertical polarized light are split by the third polarization beam splitter (412), and the horizontal polarized light sequentially passes through a first dichroic half-wave plate (413), a first polished surface reflector (414), a first crystal (415), a second polished surface reflector (416) and the third polarization beam splitter (412); the vertically polarized light sequentially passes through the second polished surface reflector (416), the first crystal (415), the first polished surface reflector (414), the first dichroic half-wave plate (413) and the third polarizing beam splitter (412), and the horizontally polarized light and the vertically polarized light are output by the third polarizing beam splitter (412) and then are converged to form a nonlinear frequency-converted light beam.
3. The device according to claim 1, wherein the nonlinear frequency conversion module (4) comprises a first focusing lens (421), a second dichroic mirror (422), a fourth dichroic polarizing beam splitter (423), a second dichroic half-wave plate (424), a seventh reflecting mirror (425), a second crystal (426), an eighth reflecting mirror (427), and a first collimating lens (428), the input light beam passes through the first focusing lens (421), the second dichroic mirror (422), and the fourth dichroic polarizing beam splitter (423) in sequence and then is divided into horizontal polarized light and vertical polarized light, the horizontal polarized light passes through the second dichroic half-wave plate (424), the seventh reflecting mirror (425), the second crystal (426), the eighth reflecting mirror (427), and the fourth dichroic polarizing beam splitter (423) in sequence and then is output as a first path, and the vertical polarized light passes through the eighth reflecting mirror (427), the fourth reflecting mirror (423) in sequence and the vertical polarized light passes through the eighth reflecting mirror (427), And the second output is used as the second output after the second crystal (426), the seventh reflector (425), the second dichroic half-wave plate (424) and the fourth dichroic polarizing beam splitter (423) are mixed, and the first output and the second output are used as the output of the nonlinear frequency conversion module (4) after passing through the first collimating lens (428).
4. The vector beam-based nonlinear frequency conversion device according to claim 1, wherein the nonlinear frequency conversion module (4) comprises a second focusing lens (431), a third crystal group (432), a second collimating lens (433), and a filter (434) which are arranged in sequence.
5. The device of any one of claims 2-4, wherein the crystal is a periodically poled KTP crystal, and the vertically and horizontally polarized light is focused at the center of the crystal from two opposite directions of the crystal.
6. The device for converting nonlinear frequency based on vector light beam according to claim 1, wherein the angular momentum module (2) comprises a second polarizing beam splitter (21), a second reflecting mirror (22), a third reflecting mirror (23), a vortex phase plate (24), and a fourth reflecting mirror (25), the light beam inputted into the angular momentum module (2) is divided into horizontally polarized light and vertically polarized light by the second polarizing beam splitter (21), and the horizontally polarized light passes through the second reflecting mirror (22), the third reflecting mirror (23), the vortex phase plate (24), and the fourth reflecting mirror (25) in sequence, and then is outputted by the second polarizing beam splitter (21); the vertically polarized light sequentially passes through a fourth reflector (25), a vortex phase plate (24), a third reflector (23) and a second reflector (22) and then is output by a second polarizing beam splitter (21), and two paths of light beams output by the second polarizing beam splitter (21) are mixed and then serve as output light beams of the angular momentum module (2).
7. The vector beam-based nonlinear frequency conversion device according to claim 1, wherein a first measurement module (3) is further disposed between the angular momentum module (2) and the nonlinear frequency conversion module (4), the first measurement module (3) includes a third quarter-wave plate (31), a fifth mirror (32), a fourth quarter-wave plate (33), a sixth mirror (34), and a first CCD element (36), the third quarter-wave plate (31), the fifth mirror (32), and the fourth quarter-wave plate (33) are sequentially disposed on an optical path between the angular momentum module (2) and the nonlinear frequency conversion module (4), and light reflected by the fifth mirror (32) is reflected to the first CCD element (36) through the sixth mirror (34).
8. The vector beam based nonlinear frequency conversion apparatus according to claim 1, wherein the output end of the nonlinear frequency conversion module (4) is further provided with a second measurement module (5), and the second measurement module (5) comprises a fifth quarter wave plate (52) and a second CCD element (54) which are arranged on the output optical path of the nonlinear frequency conversion module (4).
9. The vector beam-based nonlinear frequency conversion apparatus according to claim 1, wherein the light processing module (1) comprises a circularly polarized light acquisition module, and the circularly polarized light acquisition module comprises a second half-wave plate (141) and a second quarter-wave plate (142) which are arranged in sequence.
10. The vector light beam-based nonlinear frequency conversion device according to claim 9, wherein the light processing module (1) further comprises a light generation module and a light adjustment module sequentially disposed at a front end of the circularly polarized light acquisition module, and the light adjustment module comprises a first half-wave plate (112), a first quarter-wave plate (113), and a first polarization beam splitter (12) sequentially disposed along a light path.
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