Laser homogenization system based on aspheric beam shaping

Abstract

The invention provides a laser homogenization system based on aspheric light beam shaping. The laser homogenization system comprises a laser, and a first beam expanding lens group, an aspheric shaping lens group, a second beam expanding lens group, a diaphragm and a third beam expanding lens group which are sequentially arranged along a light path where to-be-homogenized laser emitted by the laser is located, the laser serves as a point light source to emit laser to be homogenized; the first beam expanding lens group is used for carrying out primary beam expanding on laser emitted by the laser device to obtain primary uniform light beams; the aspheric shaping lens group collimates and homogenizes the primary uniform light beam to obtain a collimated light beam; the second beam expanding lens group performs secondary beam expanding on the collimated light beam to obtain a secondary uniform light beam; a diaphragm hole with an adjustable aperture is formed in the diaphragm, and the diaphragm performs apodization processing on the secondary uniform light beam to obtain a high-uniformity central light beam; and the third beam expanding lens group performs three-stage beam expanding on the central light beam to obtain a target uniform light beam, and the diameter of the target uniform light beam can be adjusted by adjusting the aperture of the diaphragm hole.

Description

Technical Field

[0001] The present invention relates to the technical field of laser shaping, and provides a laser homogenization system based on aspherical beam shaping. Background Art

[0002] The spatial intensity of the laser beam emitted by a laser is Gaussian-distributed, that is, a Gaussian beam. In an illumination system with a laser as the light source, it is necessary to shape the Gaussian beam into a uniform beam, and the beam uniformity directly affects the uniformity and repeatability of applications such as optical detection and laser processing.

[0003] There are many methods for obtaining a highly uniform beam from a Gaussian beam. Initially, methods of hard-edge aperture interception and integrating sphere homogenization were adopted. These two methods are simple and direct, but the energy utilization rate is very low, and there are obvious near-field diffraction effects when the aperture of the hard-edge aperture is small, and integrating sphere homogenization will cause beam pulse broadening, affecting subsequent applications. Subsequently, in order to solve the problem of low energy utilization rate, various non-destructive beam shaping technologies have been studied successively to achieve the flat-top homogenization of the laser Gaussian beam. The main methods include the following: aspherical beam shaping method, microlens array beam shaping method, liquid crystal spatial light modulator, and anti-Gaussian coating method, etc.

[0004] Among the various popular non-destructive shaping technologies, the microlens array beam shaping method is to let the incident light pass through the microlens array and be divided into several sub-beams, that is, first divide the wavefront and then focus through a Fourier lens. Each sub-beam is converged by a focusing lens on the specified image plane, and the superposition of each sub-beam on the image plane, so a uniform beam can be obtained at the image plane. The main principle of the liquid crystal spatial light modulator for shaping the Gaussian beam is to change the transmittance by rearranging the electro-optic liquid crystal molecules. First, calculate the difference between the input light field, the output light field, and the desired output light field, and then calculate the transmittance corresponding to each position according to the obtained difference, and then control the liquid crystal spatial light modulator to change the refractive index and transmittance, thus realizing the shaping of the beam. The anti-Gaussian coating method is to achieve different transmittances corresponding to different positions by coating a gradient film layer. First, measure the energy distribution of the Gaussian beam, and then coat the film layer according to the anti-Gaussian law. The central transmittance is low and the edge transmittance is high, so as to form a complement with the incident Gaussian beam, and finally obtain a flat-top uniform beam.

[0005] The aspherical beam shaping technology mainly uses a beam shaping system composed of two aspherical lenses in a Galilean or Keplerian form. This shaping system can be regarded as an inverted telescopic system composed of two transmissive aspherical lenses. In fact, a uniform flat-top beam can be obtained on the output surface with only one aspherical mirror. However, at this time, the flat-top beam on the output surface is divergent, and the uniformity will seriously decrease as the propagation distance increases. Therefore, the action distance of the flat-top beam is limited. For this reason, two aspherical lenses need to be designed. The first aspherical mirror first homogenizes the beam, and the second aspherical lens collimates the beam. This method is simple, stable, reliable, and has a high energy utilization rate. However, the aperture of the output beam cannot be easily adjusted, and it has strict requirements on the distribution of the incident beam, and the beam homogenization effect is not ideal enough. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention provides a laser homogenization system based on aspherical beam shaping, including:

[0007] A laser and a first beam expander group, an aspherical shaping mirror group, a second beam expander group, a diaphragm, and a third beam expander group that are sequentially arranged along the optical path of the laser beam to be homogenized emitted by the laser;

[0008] The laser emits the laser beam to be homogenized as a point source;

[0009] The first beam expander group performs primary beam expansion on the laser beam emitted by the laser to obtain a primary uniform beam;

[0010] The aspherical shaping mirror group collimates and homogenizes the primary uniform beam to obtain a collimated beam;

[0011] The second beam expander group performs secondary beam expansion on the collimated beam to obtain a secondary uniform beam;

[0012] The diaphragm is provided with a diaphragm hole with an adjustable aperture, and the diaphragm performs apodization processing on the secondary uniform beam to obtain a central beam with high uniformity;

[0013] The third beam expander group performs tertiary beam expansion on the central beam to obtain a target uniform beam.

[0014] Specifically, the first beam expander group includes a first lens and a second lens.

[0015] Specifically, the aspherical shaping mirror group includes an aspherical incident lens and an aspherical exit lens.

[0016] Specifically, the steps for solving the aspherical surface type parameters of the aspherical shaping mirror group are as follows:

[0017] S1: Establish an input-output beam distribution model. The incident light uses a fundamental mode Gaussian beam, and the output light uses a flat-top Lorentz distribution beam;

[0018] S2: Establish a mapping relationship between the incident light and the outgoing light according to the law of conservation of energy. The so-called law of conservation of energy means that assuming the system is a lossless system, the energy within the areas included in the input surface and the output surface is equal:

[0019] ,

[0020] In the formula, is the light intensity distribution of the incident light beam; is the light intensity distribution of the outgoing light beam; is the area microelement of the incident light beam; is the area microelement of the incident light beam;

[0021] In the rectangular coordinate system, it can be expressed as:

[0022] ,

[0023] In the formula, is the coordinate of the incident light beam; is the coordinate of the outgoing light beam;

[0024] S3: Obtain the corresponding relationship between the incident light beam coordinates and the corresponding outgoing light beam coordinates through the fundamental mode Gaussian beam formula and the flat-top Lorentz distribution. This is the mapping relationship. By selecting appropriate input and output models, reduce the calculation amount and calculation difficulty of the mapping relationship;

[0025] S4: Through the calculations of the above three steps, combine Fermat's principle and the law of refraction to solve the aspherical surface shape parameters.

[0026] Specifically, the second beam expander group and the third beam expander group are reflective beam expanders. The second beam expander group includes a first reflective beam expander base and a first reflector and a second reflector installed in the first reflective beam expander base; the third beam expander group is a reflective beam expander, including a second reflective beam expander base and a third reflector and a fourth reflector installed in the second reflective beam expander base.

[0027] Specifically, the first reflector and the second reflector form a 90° angle, and the third reflector and the fourth reflector form a 90° angle.

[0028] Compared with the prior art,

[0029] 1. The present invention expands the laser by combining multi-stage beam expansion, aspherical shaping, and aperture interception, and has better homogenization performance compared with a single homogenization method;

[0030] 2. Before the apodization operation using the aperture, the present invention expands the laser beam twice so that the secondary uniform light beam incident on the aperture has a relatively large diameter. Without adjusting the diameter of the aperture hole to be very small, a spot with better central uniformity can be selected, which has higher energy utilization rate. And the laser beam is homogenized by an aspherical shaping lens group. Under the condition that the homogenization performance is not greatly affected, it has the advantage that the aperture of the emitted light beam is easy to adjust.

[0031] 3. By directly expanding the incident light, the present invention can select the focal lengths of the two lenses in the first beam expander group according to the aperture of the incident light, and adjust the diameter of the primary uniform light beam. This optical path is applicable to laser beams with different apertures. Brief Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the homogenization optical path for aspherical beam shaping of the present invention.

[0033] Reference Numerals: 1. First lens; 2. Second lens; 3. Aspherical incident lens; 4. Aspherical exit lens; 5. First mirror; 6. Second mirror; 7. First reflective beam expander; 8. Aperture; 9. Third mirror; 10. Fourth mirror; 11. Second reflective beam expander. Detailed Embodiment

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The following describes the specific implementation of the present invention in detail with specific embodiments.

[0035] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0036] A laser homogenization system based on aspherical beam shaping includes a laser and a first beam expander group, an aspherical shaping lens group, a second beam expander group, an aperture 8, and a third beam expander group that are sequentially arranged along the optical path of the laser beam to be homogenized emitted by the laser. The laser beam to be homogenized undergoes multi-stage shaping of "beam expansion - beam homogenization - beam expansion" to obtain a homogenized beam with high uniformity and no pulse broadening, and the aperture of the beam can be conveniently adjusted according to requirements.

[0037] The laser emits the laser beam to be homogenized with a Gaussian distribution of spatial intensity as a point source.

[0038] The first beam expander group includes a first lens 1 and a second lens 2, which perform primary beam expansion on the laser to be homogenized, increase the aperture of the outgoing light, and obtain a primary uniform light beam.

[0039] The aspherical shaping lens group includes an aspherical incident lens 3 and an aspherical outgoing lens 4. The shape of the aspherical lens is used to correct the propagation path of the light, and the beam intensity is homogenized by changing the phase distribution of the beam. Compared with traditional spherical lenses, aspherical lenses can reduce spherical aberration and other optical aberrations, thereby improving the imaging quality. The primary uniform light beam is refracted by the aspherical incident lens 3 to redistribute the energy, reduce the intensity fluctuations and peaks in the beam, improve the uniformity and stability of the beam, and is collimated by the aspherical outgoing lens 4 to obtain a collimated light beam.

[0040] Although a single aspherical mirror in the aspherical shaping lens group can obtain a uniform flat-top light on the output surface, the flat-top light on the output surface is divergent at this time, and the uniformity will seriously decrease as the propagation distance increases. Therefore, the working distance of the flat-top light is limited. For this reason, two aspherical lenses need to be designed. The aspherical incident lens 3 first homogenizes the beam, and the aspherical outgoing lens 4 collimates the beam.

[0041] The solution steps for the aspherical surface parameters are as follows:

[0042] S1: Establish an input-output beam distribution model. The incident light adopts a fundamental mode Gaussian beam, and the outgoing light adopts a flat-top Lorentz distribution beam;

[0043] S2: According to the law of conservation of energy, establish the mapping relationship between the incident light and the outgoing light; the so-called law of conservation of energy means that assuming the system is a lossless system, the energy within the areas included in the input surface and the output surface is equal:

[0044] ,

[0045] In the formula, is the light intensity distribution of the incident light beam; is the light intensity distribution of the outgoing light beam; is the area microelement of the incident light beam; is the area microelement of the incident light beam;

[0046] In the rectangular coordinate system, it can be expressed as:

[0047] ,

[0048] In the formula, is the coordinate of the incident light beam; is the coordinate of the outgoing light beam;

[0049] S3: Solve the mapping relationship, that is, solve the above integral function relationship. The corresponding relationship between the incident beam coordinates and the corresponding outgoing beam coordinates can be obtained through the fundamental mode Gaussian beam formula and the flat-top Lorentz distribution. This is the mapping relationship. By selecting appropriate input and output models, the calculation amount and difficulty of the mapping relationship can be reduced;

[0050] S4: Solve the aspheric surface type parameters. Through the calculations of the above three steps and combined with Fermat's principle and the law of refraction, the aspheric surface type parameters are solved.

[0051] Furthermore, the focal lengths of the first lens 1 and the second lens 2 in the first beam expander group can be selected according to the aperture of the incident light to adjust the diameter of the first-level uniform beam. This optical path is applicable to laser beams of different apertures. By adjusting the distance between the first lens 1 and the second lens 2 in the first beam expander group, the parallelism of the first-level uniform beam is ensured; by adjusting the distance between the aspheric incident lens 3 and the aspheric outgoing lens 4, the parallelism of the collimated beam is ensured.

[0052] The second beam expander group is a reflective beam expander, including the base of the first reflective beam expander 7 and the first reflector 5 and the second reflector 6 installed in the base of the first reflective beam expander 7. The collimated beam is incident into the second beam expander group, and the collimated beam is expanded at the second level through the refraction of the first reflector 5 and the second reflector 6 to obtain a second-level uniform beam.

[0053] A diaphragm 8 is arranged in the path of the second-level uniform beam, and a diaphragm hole with an adjustable aperture is arranged in the diaphragm 8 to perform apodization processing on the second-level uniform beam. When the large-diameter second-level uniform beam passes through the diaphragm hole, the diaphragm 8 physically blocks part of the edge light, and only allows the central beam with better uniformity to pass through, thereby further improving the uniformity of the beam and obtaining a central beam with high uniformity.

[0054] The traditional hard-edge diaphragm 8 interception method uses an extremely small diaphragm hole to obtain the central beam of the laser, but the energy utilization rate is very low, and there is an obvious near-field diffraction effect when the aperture of the hard-edge diaphragm is small. And the traditional integrating sphere homogenization will cause the beam pulse to broaden, affecting subsequent applications. In the present invention, the laser is expanded twice by the first beam expander group and the second beam expander group before using the diaphragm 8 for apodization operation, so that the second-level uniform beam incident on the diaphragm 8 has a large diameter. Without adjusting the diameter of the diaphragm hole to be very small, a spot with better central uniformity can be selected, and it has a higher energy utilization rate.

[0055] The diameter of the emitted central beam can be adjusted by finely tuning the aperture size of the aperture stop, thereby adjusting the diameter of the target uniform beam. Before using the aperture stop 8 for apodization operation, the aspherical beam shaping lens group is used to homogenize the laser beam. Adjusting the aperture size of the aperture stop will not have a great impact on the uniformity of the emitted central beam, thereby improving the convenience of adjusting the diameter of the central beam.

[0056] The third beam expander group is a reflective beam expander, including the base of the second reflective beam expander 11 and the third mirror 9 and the fourth mirror 10 installed in the base of the second reflective beam expander 11. The central beam enters the third beam expander group, and the central beam is expanded three times through the refraction of the third mirror 9 and the fourth mirror 10 to obtain a target uniform beam that meets the usage requirements.

[0057] In the second beam expander group and the third beam expander group, the first mirror 5 and the second mirror 6 form a 90° angle, the third mirror 9 and the fourth mirror 10 form a 90° angle, and the second mirror 6 and the third mirror 9 are arranged in parallel and emit and expand in the same direction to ensure that the aperture stop 8 does not deform.

[0058] In the entire homogenization optical path, there are no light rays that are reflected or refracted back and forth multiple times, so laser homogenization without pulse broadening can be achieved.

[0059] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A laser homogenization system based on aspheric beam shaping, characterized in that: include: A laser and a first beam expander group, an aspheric shaping lens group, a second beam expander group, an aperture and a third beam expander group which are sequentially arranged along the optical path of the laser to be homogenized emitted by the laser; The laser acts as a point light source to emit laser light to be homogenized; The first beam expander group performs primary beam expansion on the laser emitted by the laser to obtain a primary uniform beam; The aspheric shaping lens group performs beam collimation and homogenization on the primary uniform light beam to obtain a collimated light beam; The second beam expander group performs secondary beam expansion on the collimated light beam to obtain a secondary uniform light beam; The diaphragm is provided with an diaphragm hole with adjustable aperture, and the diaphragm performs a toe-cutting process on the secondary uniform light beam to obtain a central light beam with high uniformity; The third beam expander group performs three-stage beam expansion on the central light beam to obtain a target uniform light beam.

2. The laser homogenization system based on aspheric beam shaping according to claim 1, characterized in that: The first beam expander lens assembly includes a first lens and a second lens.

3. The laser homogenization system based on aspheric beam shaping according to claim 1, characterized in that: The aspheric shaping lens assembly comprises an aspheric incident lens and an aspheric exit lens.

4. The laser homogenization system based on aspheric beam shaping according to claim 4, characterized in that: The steps for solving the aspheric surface parameters of the aspheric shaping lens group are as follows: S1: Establish the input and output beam distribution model. The incident light adopts the fundamental mode Gaussian beam, and the output light adopts the flat-top Lorentz distribution beam. S2: According to the law of conservation of energy, the mapping relationship between the incident light and the outgoing light is established; the so-called law of conservation of energy means that when the system is assumed to be a lossless system, the energy within the area covered by the input surface and the output surface is equal: ， In the formula, is the light intensity distribution of the incident light beam; is the intensity distribution of the outgoing beam; is the area element of the incident beam; is the area element of the incident beam; In the rectangular coordinate system it can be expressed as: ， In the formula, is the incident beam coordinate; is the outgoing beam coordinate; S3: The corresponding relationship between the coordinates of the incident beam and the corresponding coordinates of the outgoing beam is obtained through the fundamental mode Gaussian beam formula and the flat-top Lorentz distribution. This is the mapping relationship. By selecting appropriate input and output models, the calculation amount and difficulty of the mapping relationship can be reduced. S4: Through the calculation of the above three steps, combined with Fermat's principle and the law of refraction, the aspheric surface parameters are solved.

5. The laser homogenization system based on aspheric beam shaping according to claim 1, characterized in that: The second collimator mirror group and the third collimator mirror group are reflective collimators, the second collimator mirror group includes a first reflective collimator base and a first reflector and a second reflector installed in the first reflective collimator base; the third collimator mirror group is a reflective collimator, including a second reflective collimator base and a third reflector and a fourth reflector installed in the second reflective collimator base.

6. The laser homogenization system based on aspheric beam shaping according to claim 6, characterized in that: The first reflector and the second reflector form an angle of 90°, and the third reflector and the fourth reflector form an angle of 90°.

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