CN110865462B - Off-axis reflection free-form surface laser shaping system - Google Patents
Off-axis reflection free-form surface laser shaping system Download PDFInfo
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- CN110865462B CN110865462B CN201911198552.7A CN201911198552A CN110865462B CN 110865462 B CN110865462 B CN 110865462B CN 201911198552 A CN201911198552 A CN 201911198552A CN 110865462 B CN110865462 B CN 110865462B
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Abstract
The invention discloses an off-axis reflection free-form surface laser shaping system, and belongs to the technical field of laser beam shaping. The off-axis reflection shaping system is designed by dividing the cross section profile of a light beam into M multiplied by N grids according to equal energy, dividing a target surface into M multiplied by N grids according to equal area, enabling all sampling light rays emitted by a light source to reach the target surface to meet the requirement of equal optical path length, and establishing an iterative relationship between two adjacent sampling points on a free curved surface according to the mapping relationship between input and output; the off-axis multi-reflection laser shaping system can be designed by using the method, the efficiency is high, the uniformity is good, the output light beam is a collimated light beam, and the beam expansion rate can be controlled simultaneously.
Description
Technical Field
The invention relates to an off-axis reflection free-form surface laser shaping system, and belongs to the field of laser shaping.
Background
Currently, laser has been widely used for laser processing, 3D printing, liquid crystal panel annealing, laser illumination, and the like as a light source with high brightness. However, the light intensity distribution of the laser is generally gaussian and has important limitation on the above-mentioned use scenario, so that the method has very important significance in converting the light intensity distribution of the laser from gaussian distribution to uniform distribution by designing a reasonable shaping system.
Common laser shaping methods are liquid crystal spatial light modulators [ spatial shaping of laser beams using liquid crystal spatial light modulators [ J ] optics, 2001,21 (9): 1107-: university of continental engineering, 2009), and optical free form surfaces [ penamant, suaeping. These shaped systems are all coaxial transmissive systems. The liquid crystal spatial light modulator is used as a shaping system, the light efficiency is low, and the interference effect is easily generated when the micro-lens array is used for shaping the laser. The shaping is carried out by using a binary optical element, the efficiency is not high, high-power laser cannot be borne, the aspheric lens is of a rotational symmetric structure, and non-rotational symmetric light spots such as rectangular light spots cannot be generated. Moreover, these systems are coaxial transmission systems, and the light path cannot be bent, and cannot form a compact structure. The off-axis reflection free-form surface system can be used for turning a light path to form a compact structure, the reflection system is non-dispersive and is adaptive to various wavelengths, the light efficiency is high, the system can control the uniformity of output light irradiance, can control the output light beam to be a collimated light beam, can control the beam expansion rate of the output light beam, and has very important significance for laser processing, 3D printing, liquid crystal panel annealing, laser illumination, pumping solid-state laser or fiber laser.
Existing algorithms require optimization with commercially available optical software. The commercial software is essentially a trial and error method in the optimization process, light rays are traced once when each group of surface shape data is changed in the optimization process, irradiance distribution data is calculated, the previous group of surface shape data is abandoned if irradiance uniformity is better than that of the previous group, the latest surface shape data is used, if irradiance uniformity generated by the group of surface shape data is not better than that of the previous group of surface shape data, the upper group of surface shape data is kept, and then the process is continuously repeated until the uniformity meets the target requirement. Each time optimization is carried out for 1 time, 50-100 ten thousand rays are traced, the calculation amount is very large, if the initial surface shape deviates from the final surface shape relatively far, the optimization process is easy to fall into a local minimum value, and if constraint conditions such as output wave front and beam expansion rate are added, the optimization is more difficult.
Disclosure of Invention
In order to solve at least one problem, the invention provides an off-axis reflecting free-form surface laser shaping system, which not only can realize uniform distribution of irradiance of output laser on a target surface, but also can control the wave front of an output laser beam to enable an output beam to be a collimated beam, and when the collimated beam is subjected to laser processing, the distance between the collimated beam and the target surface has a large adjustment tolerance. In addition, the off-axis double-reflection free-form surface system can control the uniformity of an emergent beam and the wavefront can also control the beam expansion ratio, namely the ratio of the calibers of the emergent beam and the input beam.
The method of the invention does not optimize the surface shape, but directly calculates the sampling points on the two free curved surfaces according to the energy mapping relation and the relation between the input and output wave fronts, and then introduces the data points into the structure design software to obtain the two free curved surfaces. The design results were then verified in optical simulation software. The design result is verified only by tracing the light ray once without any optimization, the output light beam generates uniform irradiance distribution on the target surface, the output light beam is collimated light beam, and the beam expansion ratio reaches a preset value.
The off-axis reflecting free-form surface laser shaping system can realize light path steering and compact system structure, can realize that an output light beam is changed into a light beam with uniformly distributed light intensity, and can control the output light beam to be a collimated light beam and the multiplying power of beam expansion, and can ensure that the system has wider industrial application range.
A first object of the present invention is to provide an off-axis reflective free-form surface laser shaping system, comprising two free-form surface mirrors; the two free-form surface reflectors are in off-axis relation and cannot be coaxial; the first free-form surface reflector (reflector P) and the second free-form surface reflector (reflector M) keep an off-axis relation, namely the reflectors P and M cannot be mutually shielded in the vertical direction; mirror P is to the right of M in the horizontal direction.
In one embodiment, the system further comprises an incident laser beam cross section and a receiving target surface;
in one embodiment, the cross-sectional position of the incident beam and the position of the target surface are determined according to the dimensions reserved for the laser shaping system, the size of the target surface is determined by the size of the surface of the workpiece to be machined, the size of the clear aperture of the mirror P is equal to the size of the clear aperture of the incident beam, and the clear aperture of the mirror M is equal to the size of the aperture of the outgoing beam. Point 1P on mirror P11The position is located on the emergent ray path of the 1 st point on the incident beam section, and the distance between the position and the 1 st point on the section is not strictly limited and is mainly based on the reserved space of the whole system. First point M on the mirror11On a reverse extension from a first point on the target surface, the reverse extension being perpendicular to the target surface. Point M11And the 1 st point T on the target surface11The distance between them is not strictly limited, mainly according to the whole systemThe space left.
A second object of the present invention is to provide a design method of the off-axis reflective free-form surface laser shaping system of the present invention.
In one embodiment, the method for designing an off-axis reflective free-form surface laser shaping system mainly includes: (1) dividing the laser beam by an equal-energy grid and dividing the irradiation target surface by an equal area; (2) based on division grid points and initial conditions, the free-form surface reflector is constructed by applying an energy mapping relation and an aplanatic principle.
In one embodiment, the operation steps of the equal-energy gridding laser beam and the equal-area dividing irradiating the target surface are as follows:
the incident section S is divided into M × N meshes, each mesh having equal energy, and the target surface T is divided into M × N meshes, each mesh being divided by an equal area. After the meshing is finished, the coordinate sum of the coordinates of each grid point on the cross section of the incident beam and the target surface is uniformly known and is used as an initial condition for calculating the two free-form surface reflectors, and each grid point on the cross section of the incident beam emits one light ray which is parallel to each other and is used as a sampling light ray.
In one embodiment, the operation steps of constructing the free-form surface mirror based on the division grid points and the initial conditions by applying the energy mapping relation and the aplanatic principle are as follows:
(1) setting constraint conditions and initial conditions: (a) the input light beam and the output light beam satisfy a predetermined energy mapping relation; (b) all the light rays from the cross section of the incident light beam to the target surface meet the condition of equal optical path;
(2) based on the two constraint conditions and the initial condition, the iterative relationship between adjacent sampling points on the free-form surface can be obtained, so that all the sampling points on the whole free-form surface are calculated.
In one embodiment, the step (1) is:
the incident beam is a collimated beam with a rectangular caliber or a square, the target surface is in a rectangular or square shape, the section of the incident beam is the position of the beam waist, the position is preset, and the size and the position of the target surface are also preset as initial conditions; the incident beam cross-section and the grid points on the target surface can all be calculated as initial conditions.
A first sampling light ray emitted from a first point on the input section is reflected by the first points of the reflectors P and M respectively and then enters the first point on the target surface. A first sampled ray emerging from a first point on the input cross-section is reflected by the first point of mirror P and hits the first point on the second mirror M. Knowing the incident ray vector and the emergent ray vector of the 1 st point on the first reflector, the normal vector of the 1 st point of the first reflector can be obtained, the tangent plane of the 1 st point of the first reflector can be obtained according to the normal vector, and the intersection point of the ray emergent from the 2 nd point of the light source surface and the tangent plane of the 1 st point of the first reflector is the second point. The ordinate of the 2 nd point on the second reflecting mirror is the same as the comprehensive coordinate of the corresponding 2 nd point on the target surface, and the abscissa of the 2 nd point on the second reflecting mirror can be obtained according to the aplanatic condition. The first curve on the first reflector can be obtained by repeating the above process, and is called as a seed curve, and the first curve on the second reflector can also be obtained as a seed curve, and all other sampling points on each reflector can be calculated by using a seed curve expanding method.
In one embodiment, the step (1) is specifically:
the coordinates of first points on the free-form surface mirrors P and M, P, are determined beforehand11(x′11,y′11,z′11) And M11(x″11,y″11,z″11) Referred to herein as the initial point, (where, x'11,y′11,z′11Is P11Coordinates of points, x ″)11,y″11,z″11Is a point M11Coordinates of (A), S11The first point on the first curve), P11(x′11,y′11,z′11) At the slave S11(x11,y11,z11) On the light ray of point emergence, S11And P11In the horizontal directionThe distance is not strictly required and is determined according to the size of the system; m11And T11On the same horizontal line, the distance between the two is not critical, and P is determined according to the size of the system11And M11Is chosen to follow the distribution requirements of the free-form surface mirrors P and M.
From an initial point S on the incident beam cross-section S11(x11,y11,z11) The emergent ray passes through the initial point P on the reflector P and M11(x′11,y′11,z′11) And M11(x″11,y″11,z″11) Initial point T incident on target surface T after reflection11(ii) a Light ray S11P11Through P11After point reflection, the emergent ray is P11M11So that the incident light S can be obtained11P11And an emergent ray P11M11The light vector of (2) is as shown in equation (1):
wherein Int is the incident ray vector, Out11Is the outgoing ray vector.
From the vector form (2) of the law of reflection, P passing through the mirror P can be calculated11Point normal vector N11；
Using the same method, depending on the incidence at M11Light ray P11M11And through M11Light ray P emergent after reflection11T11The passing point M can be calculated11Normal vector N'11。
When P is calculated11Point normal vector N11Can find P11The tangent plane of the point, calculating a second point P on the reflecting plane P according to the known conditions12(P12Is the second point on the first curve); from point S on the beam cross-section12To emit light and pass P11The point tangent planes intersect, and the intersection point is the second point P on the reflecting surface P12(ii) a Then, the second point M on the M surface is obtained12(ii) a Since the outgoing beam is controlled to be a plane wavefront, that is, the outgoing beam is perpendicular to the target surface, and the incoming beam is also a plane wavefront, the optical paths of the respective beams are equal when the outgoing beam comes from the cross section of the incoming beam onto the target surface, and equation (3) gives the condition that the optical paths of the first beam and the second beam are equal, where [ [ solution ] ]]Representing an optical path;
[S11P11]+[P11M11]+[M11T11]＝[S12P12]+[P12M12]+[M12T12] (3)
for ray 2, when point P is12After calculation [ S12P12]It is known that M is the plane wave because the outgoing beam is a plane wave12And T12Having the same ordinate, M can be determined from equation (3)12The abscissa of the point is; by repeating the above process, the 1 st curve on the 1 st free-form surface mirror P can be obtained, and this curve can be called a seed curve, and the 1 st curve on the mirror M can also be obtained in the same way.
In one embodiment, the step (2) is:
after determining the seed curve 1, returning to the initial point to calculate the curve 2 on the free-form surface, and continuously repeating the process to calculate the sampling point on the curve 3 from the curve 2; by expanding, all data points of all data points on the reflecting surfaces P and M can be calculated, and the specific data of the reflection can be obtained.
In one embodiment, the step (2) is specifically:
after determining the seed curve 1, returning to the initial point to calculate the next curve on the free-form surface, passing P11Point tangent plane and point S21(S12A first point on a second curve) of the light ray r emitted by the light source21The intersection point is the first point P on the curve 221(ii) a Determining a point P21Then, according to the aplanatic principle and the collimation emergent condition, the point M on the reflecting surface can be calculated21Repeating the above process to calculate a second curve on the mirrors P and M; continuing to repeat the above process, the sampling point on curve 3 can be calculated from curve 2. By expanding, all data points on the reflecting surfaces P and M can be calculated; the reflection surfaces P and M can be obtained.
A third object of the present invention is a laser machining apparatus including the off-axis reflective freeform laser shaping system of the present invention.
In one embodiment, the laser shaping system further comprises a laser light source, a workpiece to be processed and a workpiece console.
A fourth object of the invention is a 3D printer comprising the off-axis reflective freeform laser shaping system of the invention.
In one embodiment, the laser shaping system further comprises a power supply system, a control system and a driving system.
A fifth object of the present invention is a liquid crystal panel annealing apparatus comprising the off-axis reflective freeform laser shaping system of the present invention.
In one embodiment, the laser shaping system further comprises a laser light source, a liquid crystal panel and a liquid crystal panel moving control platform.
A sixth object of the present invention is a laser illumination system comprising the off-axis reflective freeform laser shaping system of the present invention.
In one embodiment, a laser light source is included in addition to the laser shaping system of the present invention.
A seventh object of the present invention is a laser pumping system comprising the off-axis reflective free-form surface laser shaping system of the present invention, which can be used as a pumping source of a solid-state laser or a fiber laser.
The invention has the beneficial effects that:
(1) the off-axis double-reflection free-form surface laser shaping system has a compact structure, not only can enable the irradiance distribution of an output light beam to be uniform, but also can control the output light beam to be a collimated light beam, and can also control the beam expansion rate, namely the aperture ratio of the output light beam to an input light beam.
(2) Two shaping systems are designed based on the invention, a square Gaussian beam with the size of 16mm multiplied by 16mm is respectively shaped into a square uniform light spot with the size of 80mm multiplied by 80mm and a rectangular uniform light spot with the size of 120mm multiplied by 20mm, and an emergent light beam is a collimated light beam. The uniformity of the square light spots is 90.74%, the beam expansion rate of the light beams is 5, the uniformity of the rectangular light spots is 94.75%, the beam expansion rate in the horizontal direction is 7.5 times, the beam expansion rate in the vertical direction is 1.25 times, and the light efficiency of the two systems reaches nearly 90%. The laser beam shaping device can shape the laser beam to generate uniform irradiance distribution, the generated light spot can be rectangular or square, the output light beam is a collimated light beam, the optical efficiency of the system is very high, the multiplying power of beam expansion can be adjusted, and the advantages can be applied to laser processing, 3D printing, laser pumping, liquid crystal panel annealing and the like.
Drawings
FIG. 1 is a schematic diagram of an off-axis double-reflection laser shaping system.
FIG. 2 is a grid division of the incident beam cross section and the target plane; (a) dividing an incident beam into equal-energy grids; (b) and (5) carrying out equal-area meshing on the target surface.
Fig. 3 is an X-direction cross-sectional irradiance distribution diagram of an incident beam on an S-plane.
Fig. 4 is a Y-direction cross-sectional irradiance distribution diagram of an incident beam on an S-plane.
Fig. 5 is a schematic diagram of the calculation of sampling points on two free-form surfaces.
FIG. 6 is a calculation of data points on the reflecting surface P; (a) calculating data points on adjacent curves; (b) calculation of all data points on the reflecting surface.
Fig. 7 is a diagram showing a structure of a collimated laser beam shaping.
FIG. 8 is a graph of irradiance; (a) an incident laser radiation illuminance distribution diagram; (b) and (4) a target surface radiation illuminance distribution diagram.
FIG. 9 is a view of elongated beam shaping; (a) a light beam shaping structure chart; (b) and (5) a target meter radiation illuminance distribution diagram.
Fig. 10 is a schematic diagram of application of the emergent beam of embodiment 1 in laser processing.
Fig. 11 is a schematic diagram of an application of a prior art shaping outgoing beam in laser processing.
Fig. 12 is a schematic view of a reflection shaping system of embodiment 1.
Fig. 13 is a schematic diagram of a conventional transmission shaping system.
Detailed Description
The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.
Example 1
As shown in fig. 1, a plane S is a cross section of an incident laser beam, light irradiance distribution on the cross section is gaussian distribution, a plane T is a target plane, P and M are two mirrors, and surfaces of the two mirrors are free-form surfaces. Thus P and M form an off-axis reflective free-form surface system. The design principle of the laser shaping system is as follows: the incident section S is divided into M × N meshes, each mesh having equal energy, and the target surface T is divided into M × N meshes, each mesh being divided by an equal area. By designing an off-axis free-form surface reflection system formed by P and M, each sub-beam passing through the S-surface grid is controlled to be incident into a corresponding grid on the target surface T after being reflected by P and M. Since each sub-beam has equal energy, each grid of the target surface has equal area, so that the entire beam passing through the shaping system and incident on the target surface will produce a uniform irradiance distribution. The following is a main discussion of how to design the two free-form mirrors P and M.
The design method of the system comprises two steps: 1. dividing the laser beam by an equal-energy grid and dividing the irradiation target surface by an equal area; 2. based on division grid points and initial conditions, the free-form surface reflector is constructed by applying an energy mapping relation and an aplanatic principle.
1. Dividing the laser beam by an equal-energy grid and dividing the irradiation target surface by an equal area;
according to the working principle of the laser shaping system, the energy of the grid on the incident beam cross section is incident to the corresponding grid on the target surface as shown in FIG. 2As shown. FIG. 2(a) the incident beam cross-section is divided into M × N grids to ensure equal energy per grid, because irradiance distribution in both horizontal and vertical directions on the cross-section is Gaussian distribution as shown in FIGS. 3 and 4, so the grid area in the central area is small and the grid area in the edge area is large; for the target surface fig. 2(b) directly divides the mxn mesh by equal area, reference can be made to the literature for incident beam cross-section and target surface meshing: (free-form surface lens design for divergent laser beam shaping; optical newspaper 36 vol.5 (pp: 522003-1.) when gridding is completed, the coordinates S of the incident beam cross section and each grid point on the target surfaceijAnd TijAs an initial condition for calculating the two free-form mirrors.
2. Free-form surface reflector constructed based on division grid points and initial conditions by applying energy mapping relation and aplanatic principle
The design process of two free-form surfaces, as shown in fig. 5, is divided into 3 steps:
(1) determining initial conditions:
the incident beam is a collimated beam with a rectangular caliber, the target surface is rectangular, the section of the incident beam is the position of the beam waist, the size and the position of the target surface are preset as initial conditions. The initial condition can be calculated from the incident beam cross-section and the grid points on the target surface. As shown in FIG. 5, a first point P on the free-form surface mirrors P and M is determined11(x′11,y′11,z′11) And M11(x″11,y″11,z″11) Referred to herein as the initiation point, P11(x′11,y′11,z′11) At the slave S11(x11,y11,z11) On the light ray of point emergence, S11And P11The distance in the horizontal direction is not critical and depends on the size of the system. M11And T11The distance between the two is not strictly required and is determined according to the size of the system.
(2) Calculating a first curve on each free-form surface:
from an initial point S on the incident beam cross-section S11(x11,y11,z11) The emergent ray passes through the initial point P on the reflector P and M11And M11Initial point T incident on target surface T after reflection11. Light ray S11P11Through P11After point reflection, the emergent ray is P11M11So that the incident light S can be obtained11P11And an emergent ray P11M11The light vector of (1).
Int＝(x′11-X11)i+(y′11-Y11)j+(z′11-Z11)k
Out11＝(x″11-x′11)i+(y″11-y′11)j+(z″11-z′11)k (1)
From the vector form (2) of the law of reflection, P passing through the mirror P can be calculated11Point normal vector N11
Using the same method, depending on the incidence at M11Light ray P11M11And through M11Light ray P emergent after reflection11T11The passing point M can be calculated11Normal vector N'11。
When P is calculated11Point normal vector N11Can find P11The tangent plane of the point, calculating a second point P on the reflecting plane P according to the known conditions12. From point S on the beam cross-section12To emit light and pass P11The point tangent planes intersect, and the intersection point is the second point P on the reflecting surface P12. Then, the second point M on the M surface is obtained12. Because the emergent beam is controlled to be plane wave front, namely the emergent beam is vertical to the target surface, and the incident beam is also plane wave front, the emergent beam emits light from the incident beam sectionIs converged on the target surface, the optical paths are equal, and the condition that the optical paths of the first light ray and the second light ray are equal is given by equation (3), wherein]The optical path length is indicated.
[S11P11]+[P11M11]+[M11T11]＝[S12P12]+[P12M12]+[M12T12] (3)
For ray 2, when point P is12After calculation [ S12P12]It is known that M is the plane wave because the outgoing beam is a plane wave12And T12The same ordinate is used to determine the abscissa according to equation (3). By repeating the above process, the 1 st curve on the first free-form surface mirror P, such as curve 1 in fig. 6(a), which may be referred to as a seed curve, can be obtained, and the 1 st curve on the mirror M can also be obtained.
(3) Calculating all sampling points on the whole free-form surface
After determining the seed curve 1, the next curve on the free-form surface is calculated back to the initial point, as shown in fig. 5. Per P11Point tangent plane and point S21Emitted light ray r21The intersection point is the first point P on the curve 221. Determining a point P21Then, according to the aplanatic principle and the collimation emergent condition, the point M on the reflecting surface can be calculated21Repeating the above process calculates a second curve on mirrors P and M. Continuing to repeat the above process, the sampling point on curve 3 can be calculated from curve 2. Expanding this way, all data points on the reflecting surfaces P and M can be calculated.
Design instance verification
The method for testing the uniformity of the illumination of the target surface comprises the following steps: to quantitatively compare the variation in uniformity of the input and output beam irradiance, the uniformity of the laser irradiance distribution was defined as follows. In the formula
As mean value of irradiance in the test area, EmaxIs the maximum value of the radiation illumination in the test area.
Example 2: shaping system designed by the method of example 1
The input light beam is a collimated laser beam, the light beam is a square aperture with the size of 8mm multiplied by 8mm, the irradiation target surface is 80mm multiplied by 80mm, and the number of grid divisions is 161 multiplied by 161. The shaping system designed according to the method is shown in fig. 7, and the radiation illuminance is shown in fig. 8: the uniformity of the illumination of the target surface reaches 91%, wherein the uniformity is the ratio of the average illumination value to the maximum illumination value on the target surface.
Example 3: shaping system designed by the method of example 1
The square caliber laser beam (the light intensity distribution of the cross section is Gaussian distribution) is shaped into a strip-shaped facula with uniform distribution. The size of the target surface in the square uniform spot shaping system is changed to 120mm multiplied by 20mm, and other parameters are kept unchanged. The system designed by the above method is shown in fig. 9(a), and the illuminance distribution on the target surface is shown in fig. 9 (b). According to simulation results, the designed reflection type shaping system can effectively shape the Gaussian-distributed rectangular-aperture laser beam into a long-strip-shaped beam, the size of an output light spot is 120mm multiplied by 20mm, and the uniformity of the radiation illumination of the target surface is 94.57%.
Example 4: application of the System of example 1 to laser machining
The system of example 1 was used in laser machining.
As can be seen from fig. 10, the light beam emitted in example 1 is a collimated light beam, the influence of the back and forth movement of the workpiece to be machined is not large, and the laser irradiance distribution is uniform on any section of the emitted light beam. In some existing shaping methods, the emergent light beam is a non-collimated light beam (shown in fig. 11), and only a uniform illumination distribution is generated on a specific surface, so that the workpiece cannot move back and forth, which brings great limitation to laser processing.
Comparison of the off-axis reflective freeform surface shaping system of example 1 with the existing transmission system:
the reflective system in embodiment 1 has a significant advantage compared with the existing transmissive system shaping, as shown in fig. 12, in order to control the size of the output beam, the reflective system needs to control the distance between two mirrors, and the larger the aperture of the output beam is, the larger this distance is, however, in fig. 13 of the transmissive system, in order to control the size of the output beam, the thickness of the lens needs to be adjusted, and if the aperture of the output beam needs to be larger, the thickness of the lens needs to be made very thick, which not only causes difficulty in processing, but also wastes materials.
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 therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (8)
1. A design method of an off-axis reflecting free-form surface laser shaping system is characterized in that the off-axis reflecting free-form surface laser shaping system comprises two free-form surface reflectors; the two free-form surface reflectors are in off-axis relation and cannot be coaxial;
the specific design process comprises the following steps: the method mainly comprises the following steps:
(1) dividing the laser beam by an equal-energy grid and dividing the irradiation target surface by an equal area;
(2) based on grid point division and initial conditions, applying an energy mapping relation and an aplanatic principle to construct a free-form surface reflector; the method specifically comprises the following steps:
firstly, determining an initial condition:
the incident beam is a collimated beam with a rectangular caliber, the target surface is rectangular, the section of the incident beam is the position of the beam waist, the position is preset, and the size and the position of the target surface are also preset as initial conditions; according to the incident beam section and the grid point on the target surface, all the calculation can be used as initial conditions to determine the first point P on the free-form surface reflectors P and M11(x′11,y′11,z′11) And M11(x″11,y″11,z″11) Referred to herein as the initiation point, P11(x′11,y′11,z′11) At the slave S11(x11,y11,z11) On the light ray of point outgoing, M11And T11On the same horizontal line as the main body;
calculating a first curve on each free-form surface:
from an initial point S on the incident beam cross-section S11(x11,y11,z11) The emergent ray passes through the initial point P on the reflector P and M11And M11Initial point T incident on target surface T after reflection11(ii) a Light ray S11P11Through P11After point reflection, the emergent ray is P11M11So that the incident light S can be obtained11P11And an emergent ray P11M11The light vector of (a) is as in formula (1);
Int＝(x′11-x 11)i+(y′11-y 11)j+(z′11-z 11)k
Out11＝(x″11-x′11)i+(y″11-y′11)j+(z″11-z′11)k (1)
from the vector form (2) of the law of reflection, P passing through the mirror P can be calculated11Point normal vector N11
Using the same method, depending on the incidence at M11Light ray P11M11And through M11Light ray P emergent after reflection11T11The passing point M can be calculated11Normal vector N'11；
When P is calculated11Point normal vector N11Can find P11The tangent plane of the point, calculating a second point P on the reflecting plane P according to the known conditions12(ii) a From a point on the beam cross-sectionS12To emit light and pass P11The point tangent planes intersect, and the intersection point is the second point P on the reflecting surface P12(ii) a Then, the second point M on the M surface is obtained12(ii) a Because the emergent beam is controlled to be plane wave front, namely the emergent beam is vertical to the target surface, and the incident beam is also plane wave front, the optical path is equal when the emergent beam is from the incident beam section to the target surface, and the formula (3) gives the condition that the optical path of the first light ray is equal to that of the second light ray, wherein]Representing an optical path;
[S11P11]+[P11M11]+[M11T11]＝[S12P12]+[P12M12]+[M12T12] (3)
for ray 2, when point P is12After calculation [ S12P12]It is known that M is the plane wave because the outgoing beam is a plane wave12And T12Have the same ordinate so that the abscissa can be found according to equation (3); repeating the above process continuously to obtain the 1 st curve on the free-form surface reflector P, which is called as seed curve, and also obtain the 1 st curve on the reflector M;
calculating all sampling points on the whole free-form surface
After determining the seed curve 1, returning to the initial point to calculate the next curve on the free-form surface, passing P11Point tangent plane and point S21Emitted light ray r21The intersection point is the first point P on the curve 221(ii) a Determining a point P21Then, according to the aplanatic principle and the collimation emergent condition, the point M on the reflecting surface can be calculated21Repeating the above process to calculate a second curve on the mirrors P and M; the above process is repeated continuously, and the sampling point on the curve 3 can be calculated from the curve 2; expanding this way, all data points on the reflecting surfaces P and M can be calculated.
2. An off-axis reflective free-form surface laser shaping system obtained by the design method of claim 1.
3. A laser machining apparatus comprising the off-axis mirrored freeform laser shaping system of claim 2.
4. A 3D printer comprising the off-axis mirrored freeform laser shaping system of claim 2.
5. An apparatus for annealing a liquid crystal panel comprising the off-axis mirrored freeform laser shaping system of claim 2.
6. A laser illumination system comprising the off-axis mirrored freeform laser shaping system of claim 2.
7. A laser pumping system comprising the off-axis mirrored free-form laser shaping system of claim 2.
8. A pump source of a solid state laser or fiber laser comprising the laser pumping system of claim 7.
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