CN112859355A - Method and system for generating vector light beam and realizing focal field customization - Google Patents
Method and system for generating vector light beam and realizing focal field customization Download PDFInfo
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- CN112859355A CN112859355A CN202110073017.XA CN202110073017A CN112859355A CN 112859355 A CN112859355 A CN 112859355A CN 202110073017 A CN202110073017 A CN 202110073017A CN 112859355 A CN112859355 A CN 112859355A
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Abstract
The invention provides a method and a system for generating vector beams and realizing focal field customization, wherein a fiber laser array generating system is used for generating a fiber laser array, and a small part of the fiber laser array is collected and used for piston phase control; carrying out polarization regulation on each sub-beam in the rest fiber laser arrays to enable the sub-beams to become vector beams with set polarization distribution; the vector light beam is emitted after being tightly focused by the high numerical aperture lens, and the vector light beam tight focusing field distribution near the focal plane is obtained; the initial polarization azimuth angle and the azimuth angle of each sub-beam in the vector beam are changed, so that the distribution of the vector beam close focusing field near the focal plane can be changed, and the customization of the focal field of the vector beam is realized. The invention is expected to obtain a high-power tightly focused vector light field, and realizes flexible regulation and control of the vector light beam focal field by carrying out polarization control on each sub-beam.
Description
Technical Field
The invention relates to the technical field of fiber laser coherent synthesis, in particular to a method and a system for generating vector beams and realizing focal field customization.
Background
The polarization state is one of the important vector properties of light. Unlike spatially uniform polarized light beams (e.g., linearly polarized light, circularly polarized light, elliptically polarized light), vector light beams have a spatially non-uniform distribution. Among the vector beams, a beam having an axisymmetric distribution of polarization states and a hollow intensity distribution is called a cylindrical vector beam.
In recent years, cylindrical vector beams have attracted much attention of researchers at home and abroad due to the characteristic tight focusing characteristic of the cylindrical vector beams. For example, a radial polarization vector beam produces an extremely strong axial light field compared to linearly polarized light to produce a focused spot smaller than linearly polarized light. The tangentially polarized vector beam will form a circular focal field distribution in the focal plane. Based on the excellent characteristics, the column vector beam has great application potential in high-resolution imaging, micro-nano processing, particle capture and other applications.
In the prior art, methods of generating a cylindrical vector beam include an active type and a passive type. Wherein the complexity of the output mode of the active generation method is limited by the laser resonator; the passive generation method requires a large optical element and a complicated optical path, the output power is affected by the nonlinear effect, the mode is unstable and the optical element bears the power, and the conversion efficiency is low.
The optical fiber laser coherent synthesis system can keep good beam quality while obtaining high power output, and has wide application value in the fields of industrial production, material processing, biomedical treatment, scientific research and the like. Based on the coherent synthesis technology, the structural light field with special spatial distribution, such as vortex light beams, Bessel Gaussian light beams and Airy light beams, can be obtained by controlling the amplitude, the phase and the polarization state of the array laser system. Based on the above analysis, it would be advantageous to use a fiber laser coherent combining system to produce a high output power column vector beam. However, no relevant report of using a fiber laser coherent combining system to generate a high output power column vector beam is known.
Disclosure of Invention
Aiming at the defects in the existing method for generating the vector beam, the invention provides a method and a system for generating the vector beam and realizing the customization of a focal field, so that the flexible customization of the focal field can be realized while the high-power output of the column vector beam is kept.
In order to achieve the technical purpose, the technical scheme of the invention is as follows:
a method of generating a vector beam and implementing focal field customization, comprising:
generating a fiber laser array by using a fiber laser array generating system;
collecting a small part of fiber laser array for piston phase control; carrying out polarization regulation on each sub-beam in the rest fiber laser arrays to enable the sub-beams to become vector beams with set polarization distribution;
the vector light beam is emitted after being tightly focused by the high numerical aperture lens, and the vector light beam tight focusing field distribution near the focal plane is obtained;
the initial polarization azimuth angle of each sub-beam in the vector beam or/and the azimuth angle of each sub-beam can be changed, so that the close focusing field distribution of the vector beam near the focal plane can be changed, and the focal field customization of the vector beam is realized.
Furthermore, the method further comprises the steps of collecting a small part of the vector light beam for observation, and checking whether the polarization direction of each sub-light beam in the vector light beam meets the requirement of the set polarization distribution.
Further, in the above method, the vector beams are distributed radially, and have N circles of annular sub-arrays arranged radially, and the larger the number of circles of the annular sub-arrays, the closer the coherently combined vector beams are to the ideal vector beams.
Further, in the above method, the beam waist radius of each sub-beam in the vector beam is w0The wavelength is lambda, the sub-aperture of the light beam is R, and the number of sub-light beams of the i-th ring of annular sub-array is MiThe distance between the center of the sub-beam of the i-th ring annular sub-array and the center of the vector beam is riThe central distance between adjacent sub-beams in the i-th ring sub-array is diThe initial polarization azimuth angle of each sub-beam in the vector beam is
Azimuth angle of each sub-beam in vector beam
The azimuth angle of the nth sub-beam of the ith annular sub-array is shown.
Further, in the above method, the expression of the initial field of the emission surface vector beam is:
wherein the content of the first and second substances,
as cylindrical coordinates of the initial plane, ErAnd
is divided intoThe initial field is r and
the directional component, circ (·) represents the truncation of the sub-beam, with values inside the radius R taking 1 and values outside the radius R taking 0. Delta-w0the/R is the truncation factor of the sub-beam, the larger the δ, the more the sub-beam is truncated.
Further, in the above method, the vector beam is tightly focused by the high numerical aperture lens, and the focal position of the tight focus is at z-0, and the distribution of the vector beam tight focusing field near the focal plane is obtained according to richard-walff's vector diffraction theory
In the formula (I), the compound is shown in the specification,
radial, tangential and axial light field components near the focus in a polar coordinate system,
is the cylindrical coordinate near the focal point, theta is the convergence angle of a point on the pupil plane, and f is the focal length of the high numerical aperture lens. Pupil apodization function
Is in the form of a Bessel-Gaussian function
Wherein, thetamax＝arcsin-1(NA) is the maximum beam convergence angle, NA is the numerical aperture of the high numerical aperture lens, NA>0.7, beta is the high numerical aperture lens fill factor.
The invention provides a system for generating vector beams and realizing focal field customization, which introduces a polarization control unit into a coherent synthesis optical fiber laser array generation system, is expected to obtain a high-power tightly focused vector light field, and realizes flexible regulation and control of the focal field of the vector beams under the action of the polarization control unit. The system comprises a seed source, a pre-amplifier beam splitter, a phase modulator array, an optical fiber amplifier, a collimator array, a beam combining device, a high-reflection mirror, a closed-loop phase control unit, a polarization control unit, a high-numerical-aperture lens and a transmitting output device;
the method comprises the following steps that after being preliminarily amplified by a preamplifier, the laser output by a seed source is divided into multiple paths of laser by a beam splitter, the phases of the lasers are adjusted by a phase modulator array, after the power of the lasers is improved by an optical fiber amplifier, the lasers are output in a collimation mode by a collimator array, the lasers output in the collimation mode by the collimator array are formed into an optical fiber laser array by a beam combining device and then are output, and the optical axes of sub-beams in the output optical fiber laser array are parallel to each other; the output fiber laser array is divided into two beams of light by a high-reflection mirror, the two beams of light are respectively sampling light and main laser, the sampling light is used as the input of a closed-loop phase control unit, the closed-loop phase control unit generates phase control quantity of each path of laser, and corresponding control voltage is applied to a phase modulator array according to the phase control quantity to realize piston phase control; the main laser carries out polarization regulation and control on each sub-beam in the fiber laser array through the polarization control unit, so that the sub-beams become vector beams with set polarization distribution, and the vector beams enter the emission output device after being tightly focused by the high numerical aperture lens.
Preferably, the closed-loop phase control unit in the system includes a lens, a photodetector and a controller, the sampling light converges on the photodetector for sampling after passing through the lens, the photodetector converts an optical signal into an electrical signal and transmits the electrical signal to the controller, and the controller obtains the phase control quantity of each path of laser by using a phase control algorithm according to the received electrical signal, so as to realize piston phase control.
Preferably, the system further includes a vector beam sampling unit, the vector beam sampling unit includes a high-reflection mirror, an analyzer, a photodetector and an oscilloscope, the vector beam output by the polarization control unit is divided into two beams by the high-reflection mirror, one of the two beams is input to the high-numerical aperture lens, the other beam is used as a sampling beam, the sampling beam sequentially passes through the analyzer and the photodetector, the photodetector outputs an optical signal to the oscilloscope for observation, and the analyzer is used to check whether the polarization direction of each sub-beam in the vector beam meets the set polarization distribution requirement.
Preferably, the polarization control unit in the above system is composed of an array of half-wave plates.
The invention can achieve the following technical effects:
(1) based on the coherent synthesis technology, the vector beam with high conversion efficiency is obtained under the regulation and control of the polarization control unit.
(2) The method can obtain the high-power vector light field and realize the flexible customization of the focal field of the vector light field.
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 structures shown in the drawings without creative efforts.
Fig. 1 is a schematic structural diagram according to an embodiment of the present invention.
Fig. 2 is a schematic arrangement diagram of emission surface vector light beams in an embodiment.
FIG. 3 is a diagram illustrating vector beams focused by a high numerical aperture lens according to an embodiment.
FIG. 4 shows the initial light intensity distribution of the radial polarization composite vector light beam and the tangential polarization composite vector light beam and the focal plane light intensity distribution under different numerical apertures in one embodiment, wherein FIG. 4(a1) is a light intensity distribution graph of radial polarized light at the emission surface, FIG. 4(a2) is a light intensity distribution graph of tangential polarized light at the emission surface, FIG. 4(b1) is the focal plane intensity distribution diagram of radially polarized light at a numerical aperture NA of 0.8, FIG. 4(c1) is the focal plane intensity profile of radially polarized light at a numerical aperture NA of 0.9, FIG. 4(d1) is a focal plane intensity distribution diagram of radially polarized light at numerical aperture NA of 1, 4(b2) is a focal plane intensity distribution diagram of tangentially polarized light at numerical aperture NA of 0.8, 4(c2) is a focal plane intensity distribution diagram of tangentially polarized light at numerical aperture NA of 0.9, and 4(d2) is a focal plane intensity distribution diagram of tangentially polarized light at numerical aperture NA of 1;
FIG. 5 is a diagram illustrating light intensity distribution and polarization state distribution of a focal plane under different initial polarization angles in an embodiment, where FIG. 5(a) is a diagram illustrating a small-sized Gaussian distribution of light intensity distribution of the focal plane when the initial polarization azimuth angle is 0, FIG. 5(b) is a diagram illustrating a flat-top distribution of light intensity distribution of the focal plane when the initial polarization azimuth angle is π/4, FIG. 5(c) is a diagram illustrating a hollow distribution of light intensity distribution of the focal plane when the initial polarization azimuth angle is π/2, FIG. 5(d) is a diagram illustrating a polarization distribution of the focal plane when the initial polarization azimuth angle is 0, FIG. 5(e) is a diagram illustrating a polarization distribution of the focal plane when the initial polarization azimuth angle is π/4, and FIG. 5(f) is a diagram illustrating a polarization distribution of the focal plane;
FIG. 6 is a diagram illustrating two-dimensional intensity distributions in the r-z direction for different initial polarization angles in an embodiment, where FIG. 6(a) is a diagram illustrating a two-dimensional intensity distribution in the r-z direction of a synthesized vector beam when the initial polarization azimuth angle is 0, FIG. 6(b) is a diagram illustrating a two-dimensional intensity distribution in the r-z direction of a synthesized vector beam when the initial polarization azimuth angle is π/4, and FIG. 6(c) is a diagram illustrating a two-dimensional intensity distribution in the r-z direction of a synthesized vector beam when the initial polarization azimuth angle is π/2;
figure 7 is a diagram of an arbitrary initial polarization distribution and its corresponding tightly-focused focal plane distribution profile in one embodiment, wherein FIG. 7(a1) is a diagram showing a polarization direction distribution of a first type of exit surface composite vector light beam, FIG. 7(b1) is a diagram showing a polarization direction distribution of a second type of exit surface combined vector light beam, FIG. 7(c1) is a diagram showing a polarization direction distribution of a third type of exit surface combined vector light beam, FIG. 7(d1) is a diagram showing a polarization direction distribution of a fourth exit surface combined vector light beam, figure 7(a2) is a close-focus focal plane view of the vector beam shown in figure 7(a1), figure 7(b2) is a close-focus focal plane view of the vector beam shown in figure 7(b1), figure 7(c2) is a close-focus focal plane view of the vector beam shown in figure 7(c1), FIG. 7(d2) is a close-focus focal plane view of the vector beam shown in FIG. 7(d 1);
reference numbers in fig. 1:
1. a seed source; 2. a preventive amplifier; 3. a beam splitter; 4. an array of phase modulators; 5. an optical fiber amplifier; 6. an array of collimators; 7. a beam combining device; 8. a first high-reflection mirror; 9. a lens; 10. an optical fiber detector; 11. a controller; 12. a polarization controller; 13. a second high-reflection mirror; 14. an analyzer; 15. a photodetector; 16. an oscilloscope; 17. a high numerical aperture lens.
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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that all the directional indicators (such as up, down, left, right, front, and rear … …) in the embodiment of the present invention are only used to explain the relative position relationship between the components, the movement situation, etc. in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indicator is changed accordingly.
In addition, the descriptions related to "first", "second", etc. in the present invention are only for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "connected," "secured," and the like are to be construed broadly, and for example, "secured" may be a fixed connection, a removable connection, or an integral part; the connection can be mechanical connection, electrical connection, physical connection or wireless communication connection; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of those skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination of technical solutions should not be considered to exist, and is not within the protection scope of the present invention.
An embodiment of the present invention provides a method for generating a vector light beam and implementing focal field customization, including:
generating a fiber laser array by using a fiber laser array generating system;
collecting a small part of fiber laser array for piston phase control; carrying out polarization regulation on each sub-beam in the rest fiber laser arrays to enable the sub-beams to become vector beams with set polarization distribution;
the vector light beam is emitted after being tightly focused by the high numerical aperture lens, and the vector light beam tight focusing field distribution near the focal plane is obtained;
the initial polarization azimuth angle of each sub-beam in the vector beam or/and the azimuth angle of the sub-beam can be changed, so that the distribution of the vector beam close focusing field near the focal plane can be changed, and the customization of the focal field of the vector beam is realized.
Referring to fig. 1, a system for generating a vector beam and implementing focal field customization provided in an embodiment includes a seed source 1, a preamplifier 2, a beam splitter 3, a phase modulator array 4, a fiber amplifier 5, a collimator array 6, a beam combiner 7, a first high-reflectivity mirror 8, a lens 9, a fiber detector 10, a controller 11, a polarization controller 12, a second high-reflectivity mirror 13, an analyzer 14, a photodetector 15, an oscilloscope 16, and a high-numerical aperture lens 17.
The method comprises the steps that laser output by a seed source 1 is preliminarily amplified by a preamplifier 2 and then is divided into multiple paths of laser by a beam splitter 3, the phases of the multiple paths of laser are adjusted by a phase modulator array 4, after power is improved by an optical fiber amplifier 5, the multiple paths of laser are output in a collimation mode by a collimator array 6, the multiple paths of laser output in the collimation mode by the collimator array 6 are formed into an optical fiber laser array by a beam combining device 7 and then are output, and optical axes of all sub-beams in the output optical fiber laser array are parallel to each other.
The output fiber laser array is divided into two beams of light by a first high-reflection mirror 8, wherein the two beams of light are respectively sampling light and main laser, and the sampling light is used as the input of a closed-loop phase control unit. The closed-loop phase control unit comprises a lens 9, a photoelectric detector 10 and a controller 11, sampling light is converged on the photoelectric detector 10 for sampling after passing through the lens 9, the photoelectric detector 10 converts an optical signal into an electric signal and transmits the electric signal to the controller 11, and the controller 11 obtains phase control quantity of each path of laser by using a phase control algorithm according to the received electric signal to realize piston phase control.
The main laser beam passes through the polarization control unit 12 to perform polarization control on each sub-beam in the fiber laser array, so that the sub-beam becomes a vector beam with a set polarization distribution. The polarization control unit 12 is composed of an array of half-wave plates. The vector beam output by the polarization control unit 12 is divided into two beams by the second high-reflection mirror 13, wherein one beam with high power is input to the high numerical aperture lens, and enters the emission output device after being tightly focused by the high numerical aperture lens 17, so that the application of a vector beam tight focusing field is realized. And the other beam of low-power light beam is taken as sampling light, the sampling light sequentially passes through the analyzer 14 and the photoelectric detector 15, the photoelectric detector 15 outputs light signals to the oscilloscope 16 for observation, and the analyzer 14 is used for detecting whether the polarization direction of each sub-beam in the vector beam meets the set polarization distribution requirement.
The vector beams are distributed radially, and have N annular sub-arrays arranged radially, as shown in fig. 2, which is a schematic view of the arrangement of the vector beams on the emission surface in one embodiment. The more number of turns of the circular sub-array in the generated vector beam, the closer the coherently combined vector beam is to the ideal vector beam. The beam waist radius of each sub-beam in the vector beam is w0Wavelength of λ, beam apertureR, the number of sub-beams of the i-th ring-shaped sub-array is MiThe distance between the center of the sub-beam of the i-th ring annular sub-array and the center of the vector beam is riThe central distance between adjacent sub-beams in the i-th ring sub-array is diThe initial polarization azimuth angle of each sub-beam in the vector beam is
Azimuth angle of each sub-beam in vector beam
The azimuth angle of the nth sub-beam of the ith annular sub-array is shown. The initial field expression of the emission surface vector beam is:
wherein the content of the first and second substances,
as cylindrical coordinates of the initial plane, ErAnd
is divided into initial fields in r and
the directional component, circ (·) represents the truncation of the sub-beam, with values inside the radius R taking 1 and values outside the radius R taking 0. Delta-w0the/R is the truncation factor of the sub-beam, the larger the δ, the more the sub-beam is truncated.
As shown in fig. 3, which is a schematic diagram of a vector light beam focused by a high numerical aperture lens in an embodiment, the vector light beam is tightly focused by the high numerical aperture lens, and z-0 is a focal position of the tight focus, and a vector light-tight focusing field distribution near a focal plane is obtained according to richard-walf vector diffraction theory
In the formula (I), the compound is shown in the specification,
radial, tangential and axial light field components near the focus in a polar coordinate system,
is the cylindrical coordinate near the focal point, theta is the convergence angle of a point on the pupil plane, and f is the focal length of the high numerical aperture lens. Pupil apodization function
Is in the form of a Bessel-Gaussian function
Wherein, thetamax＝arcsin-1(NA) is the maximum beam convergence angle, NA is the numerical aperture of the high numerical aperture lens, NA>0.7, β is the high numerical aperture lens fill factor (i.e., the ratio of the pupil radius to the beam waist radius).
When changing the initial polarization of each sub-beam in the vector beam
And azimuth angle
The distribution of the vector light beam tight focusing field near the focal plane can be changed, and the customization of the focal field of the vector light beam is realized.
To briefly explain the effect of coherent combining of vector beams according to the present invention, only a circle of vector beams arranged in circular sub-arrays is used as an example in one embodiment. In this embodiment: β is 1, the focal length f of the high numerical aperture lens is 1mm, the laser wavelength λ is 1.064nm, δ is 0.9, and the sub-beamNumber of bundles M18, the center distance d between adjacent sub-beams in the annular sub-array16.4 mm. Fig. 4(a1) and 4(a2) are light intensity and polarization distribution diagrams of the radially polarized light and the tangentially polarized light, respectively, at the emitting surface. The focal plane light intensity distributions of the radially polarized light at numerical apertures NA of 0.8, 0.9 and 1 are shown in fig. 4(b1) -4(d1), and the focal plane light intensity distributions of the tangentially polarized light at numerical apertures NA of 0.8, 0.9 and 1 are shown in fig. 4(b2) -4(d 2). As can be seen from the figure, the focal plane light intensity distribution of the coherent synthetic vector light beam under the focusing of the high numerical aperture lens is consistent with the light intensity distribution of the ideal vector light beam, the coherent synthetic radial polarized light has small-size light spots, and the coherent synthetic tangential polarized light has annular light intensity distribution. In addition, the larger the numerical aperture, the smaller the focal plane spot.
When the initial polarization azimuth angle is tried to be changed from 0 to pi/4 and then from pi/4 to pi/2, the light intensity distribution of the focal plane is gradually changed from small-size Gaussian distribution to flat-top distribution and then changed into hollow distribution (see fig. 5(a) -5(c)), so that the light intensity distribution of the focal plane can be regulated and controlled by adjusting the initial polarization azimuth angle, and the customization of the vector beam focal field is further realized. Fig. 5(d) -5(f) show polarization distributions of the focal plane at different initial polarization azimuths, with the polarization direction of the main lobe coinciding with that of the initial plane.
In order to analyze whether the synthesized vector beam has the characteristic of long focal distance near the focal point as the ideal vector beam, the light intensity distribution of the synthesized vector beam in the r-z direction is further studied. The two-dimensional intensity distribution of the resultant vector beam in the r-z direction at different initial polarization angles is shown in fig. 6. The results show that the focal length of the coherent composite vector beam reaches four wavelengths, and the lateral lengths of the flat-top distribution (fig. 6(b)) and the annular distribution (fig. 6(c)) are about 2 times that of the gaussian-like distribution (fig. 6 (a)).
Because the controllability of the sub-beams of the synthesized vector beam is strong, the focal field customization of the vector light field can be realized by adjusting the polarization direction of each sub-beam to any direction. The polarization directions of the outgoing plane combined vector beams are set as shown in fig. 7(a1) -7(d1), and fig. 7(a2) -7(d2) are focal plane light intensity distributions corresponding to array light fields of different initial polarization states. When the polarization directions of adjacent sub-apertures of the radially polarized light or the tangentially polarized light are opposite, 8 array spots in a radial arrangement can be obtained at the focal plane (fig. 7(a2) and 7(b 2)). The polarization directions of two opposite sub-apertures on the ring of the radial polarization initial array and the tangential polarization initial array are rotated by 180 degrees, and two symmetrically distributed light spots are obtained at the focal plane (fig. 7(c2) and 7(d 2)). Four examples are given here, and in fact there will be a considerable amount of specifically distributed focal field by manipulating the polarization of the sub-apertures. As the number of array control elements increases, the implementation of focal field customization will be more flexible.
In summary, although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. A method of generating a vector beam and implementing focal field customization, comprising:
generating a fiber laser array by using a fiber laser array generating system;
collecting a small part of fiber laser array for piston phase control; carrying out polarization regulation on each sub-beam in the rest fiber laser arrays to enable the sub-beams to become vector beams with set polarization distribution;
the vector light beam is emitted after being tightly focused by the high numerical aperture lens, and the vector light beam tight focusing field distribution near the focal plane is obtained;
the initial polarization azimuth angle of each sub-beam in the vector beam or/and the azimuth angle of each sub-beam can be changed, so that the close focusing field distribution of the vector beam near the focal plane can be changed, and the focal field customization of the vector beam is realized.
2. The method of claim 1, further comprising collecting a small portion of the vector beam for observation, and checking whether the polarization direction of each sub-beam in the vector beam meets the requirement of the set polarization distribution.
3. The method of claim 1 or 2, wherein the vector beams are distributed radially, and have N number of annular sub-arrays arranged radially, and the larger the number of turns of the annular sub-arrays, the closer the coherently combined vector beam is to the ideal vector beam.
4. The method of claim 3, wherein the radius of the beam waist of each sub-beam in the vector beam is w0The wavelength is lambda, the sub-aperture of the light beam is R, and the number of sub-light beams of the i-th ring of annular sub-array is MiThe distance between the center of the sub-beam of the i-th ring annular sub-array and the center of the vector beam is riThe central distance between adjacent sub-beams in the i-th ring sub-array is diThe initial polarization azimuth angle of each sub-beam in the vector beam is
Azimuth angle of each sub-beam in vector beam
＝2π(n-1)/Mi，
The azimuth angle of the nth sub-beam of the ith annular sub-array is shown.
5. The method for generating vector beams and realizing focal field customization according to claim 4, wherein the initial field expression of the emitting surface vector beam is as follows:
wherein the content of the first and second substances,
as cylindrical coordinates of the initial plane, ErAnd
is divided into initial fields in r and
the directional component, circ (·) represents the truncation of the sub-beam, with a value inside the radius R of 1 and a value outside the radius R of 0, δ ═ w0the/R is the truncation factor of the sub-beam, the larger the δ, the more the sub-beam is truncated.
6. The method of claim 5, wherein the vector beam is tightly focused by the high numerical aperture lens, and the position where z is 0 is the focal position of the tight focus, and the tight focus field distribution of the vector beam near the focal plane is obtained according to Richter-Walff vector diffraction theory
In the formula (I), the compound is shown in the specification,
radial, tangential and axial light field components near the focus in a polar coordinate system,
is a cylindrical coordinate near the focus, theta is a convergence angle of a point on the pupil plane, and f is the focal length of the high numerical aperture lens; pupil apodization function
Is in the form of a Bessel-Gaussian function
Wherein, thetamax＝arcsin-1(NA) is the maximum beam convergence angle, NA is the numerical aperture of the high numerical aperture lens, NA>0.7, beta is the high numerical aperture lens fill factor.
7. The system for generating vector beams and realizing focal field customization is characterized by comprising a seed source, a preamplifier beam splitter, a phase modulator array, an optical fiber amplifier, a collimator array, a beam combining device, a high-reflectivity mirror, a closed-loop phase control unit, a polarization control unit, a high-numerical-aperture lens and a transmitting output device;
the method comprises the following steps that after being preliminarily amplified by a preamplifier, the laser output by a seed source is divided into multiple paths of laser by a beam splitter, the phases of the lasers are adjusted by a phase modulator array, after the power of the lasers is improved by an optical fiber amplifier, the lasers are output in a collimation mode by a collimator array, the lasers output in the collimation mode by the collimator array are formed into an optical fiber laser array by a beam combining device and then are output, and the optical axes of sub-beams in the output optical fiber laser array are parallel to each other; the output fiber laser array is divided into two beams of light by a high-reflection mirror, the two beams of light are respectively sampling light and main laser, the sampling light is used as the input of a closed-loop phase control unit, the closed-loop phase control unit generates phase control quantity of each path of laser, and corresponding control voltage is applied to a phase modulator array according to the phase control quantity to realize piston phase control; the main laser carries out polarization regulation and control on each sub-beam in the fiber laser array through the polarization control unit, so that the sub-beams become vector beams with set polarization distribution, and the vector beams enter the emission output device after being tightly focused by the high numerical aperture lens.
8. The system for generating vector beams and customizing a focal field according to claim 7, wherein the closed-loop phase control unit comprises a lens, a photodetector and a controller, the sampled light is converged to the photodetector for sampling after passing through the lens, the photodetector converts an optical signal into an electrical signal and transmits the electrical signal to the controller, and the controller obtains the phase control quantity of each laser path by using a phase control algorithm according to the received electrical signal to realize piston phase control.
9. The system for generating vector beams and realizing focal field customization according to claim 7 or 8, further comprising a vector beam sampling unit, wherein the vector beam sampling unit comprises a high-reflection mirror, an analyzer, a photodetector and an oscilloscope, the vector beam output by the polarization control unit is divided into two beams by the high-reflection mirror, one beam is input to the high-numerical aperture lens, the other beam is used as sampling light, the sampling light sequentially passes through the analyzer and the photodetector, the photodetector outputs an optical signal to the oscilloscope for observation, and the analyzer is used for checking whether the polarization direction of each sub-beam in the vector beam meets the set polarization distribution requirement.
10. The system for generating vector beams and realizing focal field customization according to claim 7 or 8, wherein the polarization control unit is composed of an array of half-wave plates.
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