A device and method for controlling laser beam shape and quality

Abstract

The present invention relates to the field of laser application, and in particular to a control device and method for the shape and quality of a laser beam. The control device comprises a laser light source, a beam expander, a first reflector, a second reflector, a polarizer, a spatial light modulator, an analyzer, a first lens, a beam splitter, a second lens, a third reflector, a third lens, a CCD camera and a computer. The control method first loads a processed hybrid hologram onto a spatial light modulator, adjusts the polarization angle of the incident light beam, and then incidents on the spatial light modulator and reflects, and adjusts the reflectivity by controlling the gray value of the hybrid hologram. The image of the near field of the spatial light modulator is transmitted to the surface of a workbench for processing by using a 4f system, and the shaped light is transmitted to the CCD camera through a second 4f system by using a beam splitter for observation. The present invention utilizes the wavefront modulation characteristics of the spatial light modulator, combines the wavefront feedback technology, is simple to operate, and is flexible to use, and is an efficient and high-quality laser shaping technology.

Description

Technical Field

[0001] The present invention relates to a device and method for controlling the morphology and quality of a Gaussian beam, and in particular to a device and method for controlling the morphology and quality of a laser beam based on a spatial light modulator, and belongs to the technical field of laser application. Background Art

[0002] Laser is a kind of coherent radiation generated by the stimulation of the medium. It has excellent characteristics such as good monochromaticity, high brightness, good coherence, strong directionality and collimation, which makes the application field of laser technology very wide. Laser processing technology uses the characteristics of the interaction between laser beam and matter to process various materials including metals and non-metals, involving welding, cutting, marking, drilling, heat treatment, molding and other processing technologies. Compared with conventional mechanical processing, laser processing is more precise, accurate and rapid. In the field of aerospace, laser has become an effective means of processing special parts. At present, an important feature of international research on laser processing technology is that it covers a wide range of content and develops rapidly.

[0003] Since the intensity of the laser beam emitted by the laser presents a Gaussian distribution and the propagation path is a hyperbola, this non-uniform energy distribution characteristic will cause heat accumulation in the material in a local area, thereby destroying the material properties and affecting the consistency of the processing effect. This greatly restricts the application of laser micromachining technology in fields such as aviation and aerospace that have high requirements for device reliability.

[0004] In applications such as laser anti-counterfeiting, it is necessary to transform the circular laser spot into a hollow ring, square or other specific shape of spot. Therefore, laser beam shaping technology is extremely important. Among the many shaping methods, the aperture diaphragm method has low energy utilization and poor shaping effect. For modern industries that value efficiency, the aperture diaphragm method is far from meeting the requirements of industrialization. Microlens arrays, diffractive optical elements, telephoto depth shaping systems, birefringent lens groups, aspheric lenses and other methods can obtain shaped beams with high energy utilization or uniform beam energy distribution, but most of these methods use very expensive and sophisticated optical devices, and have a single purpose, complex optical paths and poor control flexibility, which makes it difficult to meet the requirements of simplicity and convenience. Summary of the invention

[0005] The purpose of the present invention is to provide a device for controlling the shape and quality of a laser beam, which can solve the problems of high processing cost, complex optical path and poor adaptability in the prior art.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A device for controlling the shape and quality of a laser beam, comprising a laser light source, a beam expander, a first reflector, a second reflector, a polarizer, a spatial light modulator, an analyzer, a first lens, a beam splitter, a second lens, a third reflector, a third lens, a CCD camera and a computer;

[0008] The Gaussian light emitted by the laser light source is expanded by a beam expander, and the expanded light beam is reflected by a first reflector and a second reflector in sequence, enters a polarizer to adjust the polarization angle, and then is incident on a spatial light modulator and reflected, and the reflected light enters a first lens for focusing after passing through an analyzer, and then is split by a beam splitter, a part of the light is incident on a surface of a third reflector and enters a third lens after being reflected, and the light beam shaped by the third lens enters a CCD camera for quality observation, and another part of the light is transmitted to the second lens, and the light beam acts on a workbench;

[0009] The computer is connected with the laser light source, the spatial light modulator and the CCD camera respectively.

[0010] Furthermore, the first lens and the second lens form a first 4f system, the focal length f1 of the first lens is much larger than the focal length f2 of the second lens, the first lens is located at a time of the focal length f1 behind the spatial light modulator, the second lens is located behind the first lens, and the optical distance between the second lens and the first lens is the sum of the focal lengths of the two lenses;

[0011] The first lens and the third lens form a second 4f system, the focal lengths of the first lens and the third lens are equal, the third lens is located behind the first lens, the optical path between the third lens and the first lens is the sum of the focal lengths of the two, and the CCD camera is located at one focal length behind the third lens.

[0012] Furthermore, the focal lengths of the first lens and the third lens are both 1000 mm, and the focal length of the second lens is 30 mm.

[0013] Furthermore, the beam splitter is located behind the first lens, and the optical path between the beam splitter and the first lens 8 is between f1 and 3f1.

[0014] Furthermore, the spatial light modulator is a liquid crystal spatial light modulator.

[0015] The present invention also provides a method for controlling the shape and quality of a laser beam, which is implemented by the above-mentioned control device and includes the following steps:

[0016] S1. Generate a grayscale image using the control software of the spatial light modulator or Matlab software, and then add a geometric mask to the grayscale image using mapping software to form a hybrid hologram;

[0017] S2, loading the hybrid hologram obtained in step S1 onto the spatial light modulator, adjusting the polarizer angle α1 and the angle α2 between the analyzer and the polarizer;

[0018] S3, the Gaussian light emitted by the laser light source is expanded and enters the polarizer to adjust the polarization angle, and then is incident on the spatial light modulator at an incident angle less than 10° and reflected;

[0019] S4, after the reflected light passes through the analyzer, it is split by a beam splitter;

[0020] S5. Use the first 4f system to transmit the image on the spatial light modulator to the processing table after being transmitted through the beam splitter. Use the beam splitter to transmit the 1% energy reflected light through the second 4f system to transfer the shaped light beam to the CCD camera for observation.

[0021] Furthermore, in step S1 of the above solution, the grayscales of the geometric mask area and the non-mask area in the hybrid hologram are both 0-255.

[0022] Furthermore, in step S1 of the above solution, the grayscale value of the geometric mask area in the mixed hologram is 0, and the grayscale value of the remaining grayscale images is 255.

[0023] Furthermore, in step S1 of the above solution, the grayscale value of the geometric mask area in the hybrid hologram is distributed according to an inverse Gaussian intensity distribution to improve energy utilization.

[0024] Further, in step S2 of the above scheme, the angle α1 of the polarizer is 0°, and the angle α2 between the analyzer 7 and the polarizer 5 is 0° or 90°;

[0025] In step S5, the first 4f system is composed of a first lens and a second lens, the focal length of the first lens is 1000 mm, and the focal length of the second lens is 30 mm;

[0026] The second 4f system is composed of a first lens and a third lens, and the focal length of the third lens is equal to that of the first lens.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The control device of the present invention utilizes the wavefront modulation characteristics of the spatial light modulator and combines the wavefront feedback technology. It is simple to operate and flexible to use. It is an efficient and high-quality laser shaping technology. The spatial light modulator in the present invention is easy to operate and flexible to use.

[0029] 2. The hybrid hologram used in the control method of the present invention is a graphic combining a grayscale image and a geometric mask, which does not require complex calculations and saves time.

[0030] 3. The control method of the present invention utilizes the different laser reflectances corresponding to different grayscales in amplitude modulation, and the obtained shaped light beam does not need to be filtered, thereby avoiding the interference of the spatial filter on the shaped light beam and improving the light beam quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the hybrid hologram formed in step S1 in the control method of the present invention.

[0032] Figure 2 The present invention is a schematic diagram of the principle of a device for controlling the shape and quality of a laser beam.

[0033] Figure 3 It is the reflectivity corresponding to different grayscale values ​​in step S1 of the control method involved in the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description, the purpose, technical solutions and advantages of the present invention will become clearer. It should be noted that the described embodiments are preferred embodiments of the present invention, rather than all embodiments.

[0035] Combination Figure 2 As shown, a device for controlling the shape and quality of a laser beam includes a laser light source 1, a beam expander 2, a first reflector 3, a second reflector 4, a polarizer 5, a spatial light modulator 6, an analyzer 7, a first lens 8, a beam splitter 9, a second lens 10, a third reflector 12, a third lens 13, a CCD camera 14 and a computer 15.

[0036] The Gaussian light emitted by the laser light source 1 is expanded by the beam expander 2, and the expanded light beam is reflected by the first reflector 3 and the second reflector 4 in sequence and enters the polarizer 5 to adjust the polarization angle, and then is incident on the spatial light modulator 6 and reflected. The reflected light passes through the analyzer 7 and enters the first lens 8 for focusing, and then is split by the beam splitter 9. A part of the light is incident on the surface of the third reflector 12 and enters the third lens 13 after reflection. The light beam shaped by the third lens 13 enters the CCD camera 14 for quality observation, and the other part of the light is transmitted to the second lens 10, and the light beam acts on the workbench 11 for processing. The computer 15 is connected to the laser light source 1, the spatial light modulator 6 and the CCD camera 14 respectively, and is used to control the operation of the laser light source 1, the spatial light modulator 6 and the CCD camera 14. The spatial light modulator 6 is preferably a liquid crystal spatial light modulator, and a pure phase spatial light modulator produced by Hamamatsu can be used, the model is X10468-02, and the frame rate is 60Hz. The laser light source 1 may be a picosecond laser produced by EdgeWave, with a pulse width of 12 ps and a single pulse energy of 100 μj.

[0037] The first lens 8 and the second lens 10 constitute a first 4f system, the focal length f1 of the first lens 8 is 1000 mm, the focal length f2 of the second lens 10 is 30 mm, the first lens 8 is located 1000 mm behind the spatial light modulator 6, and the second lens 10 is located 1030 mm behind the first lens 8. The reflected light from the spatial light modulator 6 passes through the first 4f system and is finally imaged into a parallel shaped light beam.

[0038] The first lens 8 and the third lens 13 form a second 4f system. The focal length of the third lens 13 is also 1000mm. The optical path of the third lens 13 after the first lens 8 is the sum of the focal lengths of the two, that is, 2000mm. The CCD camera 14 is located at an optical path of 1000mm after the third lens 13. The beam splitter 9 is located after the first lens 8, and the distance between the beam splitter 9 and the first lens 8 is between f1 and 3f1. Through the second 4f system and the beam splitter 9, 1% of the energy of the reflected light is shaped and introduced into the CCD camera 14 to observe the shape and energy distribution state of the shaped light spot. The test results show that the shaped light beam is a flat-top hexagon and a square.

[0039] The present invention also provides a method for controlling the shape and quality of a laser beam, which is implemented by the above-mentioned control device and includes the following steps:

[0040] S1. Use the control software of the spatial light modulator 6 or Matlab software to generate a grayscale image, and then use the mapping software to add a geometric mask to the grayscale image. Taking a square as an example, adjust the grayscale value of the geometric mask area to 0 and the grayscale value of the non-mask area to 255 to form Figure 1 The hybrid hologram shown, wherein the grayscale value of the geometric mask area in the hybrid hologram follows an inverse Gaussian intensity distribution;

[0041] S2, loading the hybrid hologram obtained in step S1 onto the spatial light modulator 6, moving the hologram position so that the center of the pattern coincides with the center of the laser spot, adjusting the polarizer angle α1 and the angle α2 between the analyzer 7 and the polarizer 5, adjusting the angle α1 of the polarizer 5 to 0°, and the angle α2 between the analyzer 7 and the polarizer 5 to 0° or 90°, so as to obtain the maximum amplitude modulation amount;

[0042] S3, the Gaussian light emitted by the laser light source 1 is expanded and enters the polarizer 5 to adjust the polarization angle, and the polarization direction of the incident light is adjusted to horizontal polarization. Then it is incident on the spatial light modulator 6 at an incident angle less than 10° and reflected;

[0043] S4, after the reflected light is amplitude modulated by the polarizer 7, it is split by the beam splitter 9. Figure 3As shown in the figure, the grayscale values ​​in the hologram are different, and the reflectivity is also different. In the reflected light beam, the light beam with a more uniform energy distribution in the central area of ​​the Gaussian beam is reflected by the geometric mask area, and the reflectivity is much greater than that of the non-mask area;

[0044] S5. Use the first 4f system to transmit the image on the spatial light modulator 6 through the beam splitter 9 to the processing table 11 for processing, and use the beam splitter 9 to transmit the energy 1% reflected light through the second 4f system to transmit the shaped light beam to the CCD camera for observation. In this step, the first 4f system is composed of a first lens 8 and a second lens 10. The focal length of the first lens 8 is 1000mm, the focal length of the second lens 10 is 30mm, and the second lens 10 is located 1030mm behind the first lens 8; the image is finally formed into a parallel shaped light beam through the first 4f system.

[0045] The second 4f system is composed of a first lens 8 and a third lens 13. The focal length of the third lens 13 is equal to that of the first lens 8. The optical path of the third lens 13 after the first lens 8 is the sum of the focal lengths of the two, that is, 2000 mm. The CCD camera 14 is located at an optical path of 1000 mm after the third lens 13. The beam splitter 9 is located after the first lens 8, and the distance between the beam splitter 9 and the first lens 8 is between f1 and 3f1. Through the second 4f system and the beam splitter 9, 1% of the energy of the reflected light is shaped and introduced into the CCD camera 14 to observe the shape and energy distribution state of the shaped light spot. The test results show that the shaped light beam is a flat-top beam.

[0046] The control method of the present invention can also add an automatic conversion function of the hybrid hologram, cooperate with the repetition frequency of the laser and the motion control of the platform, to achieve high-quality processing with rapid conversion of the laser beam morphology and controllable energy distribution.

[0047] The above is only a description of the preferred embodiment of the present invention, and is not intended to limit the scope of protection of the present invention. Obviously, any technician familiar with the field can easily think of replacements or changes to obtain other embodiments based on the above embodiments, which should all be included in the scope of protection of the present invention.

Claims

1. A method for controlling the shape and quality of a laser beam, implemented by a device for controlling the shape and quality of a laser beam, characterized in that: The device for controlling the shape and quality of the laser beam comprises a laser light source, a beam expander, a first reflector, a second reflector, a polarizer, a spatial light modulator, an analyzer, a first lens, a beam splitter, a second lens, a third reflector, a third lens, a CCD camera and a computer; The Gaussian light emitted by the laser light source is expanded by a beam expander, and the expanded light beam is reflected by a first reflector and a second reflector in sequence, enters a polarizer to adjust the polarization angle, and then is incident on a spatial light modulator and reflected, and the reflected light enters a first lens for focusing after passing through an analyzer, and then is split by a beam splitter, a part of the light is incident on a surface of a third reflector and enters a third lens after being reflected, and the light beam shaped by the third lens enters a CCD camera for quality observation, and another part of the light is transmitted to the second lens, and the light beam acts on a workbench; The computer is connected to the laser light source, the spatial light modulator and the CCD camera respectively. The control method comprises the following steps: S1. Generate a grayscale image using the control software of the spatial light modulator or Matlab software, and then add a geometric mask to the grayscale image using mapping software to form a hybrid hologram; S2, loading the hybrid hologram obtained in step S1 onto the spatial light modulator, adjusting the polarizer angle α1 and the angle α2 between the analyzer and the polarizer; S3, the Gaussian light emitted by the laser light source is expanded and enters the polarizer to adjust the polarization angle, and then is incident on the spatial light modulator at an incident angle less than 10° and reflected; S4, after the reflected light passes through the analyzer, it is split by a beam splitter; S5. Use the first 4f system to transmit the image on the spatial light modulator to the processing table after being transmitted through the beam splitter. Use the beam splitter to transmit the 1% energy reflected light through the second 4f system to transfer the shaped light beam to the CCD camera for observation.

2. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In the laser beam shape and quality control device, the first lens and the second lens form a first 4f system, the focal length f1 of the first lens is 1000 mm, the focal length f2 of the second lens is 30 mm, the first lens is located at a time of the focal length f1 behind the spatial light modulator, the second lens is located behind the first lens, and the optical path between the second lens and the first lens is the sum of the focal lengths of the two lenses; The first lens and the third lens form a second 4f system, the focal lengths of the first lens and the third lens are equal, the third lens is located behind the first lens, the optical path between the third lens and the first lens is the sum of the focal lengths of the two, and the CCD camera is located at one focal length behind the third lens.

3. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In the device for controlling the shape and quality of the laser beam, the beam splitter is located behind the first lens, and the optical path between the beam splitter and the first lens is between f1 and 3f1.

4. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In the laser beam morphology and quality control device, the spatial light modulator is a liquid crystal spatial light modulator.

5. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In step S1, the grayscales of the geometric mask area and the non-mask area in the hybrid hologram are both 0-255.

6. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In step S1, the grayscale value of the geometric mask area in the mixed hologram is 0, and the grayscale of the remaining grayscale images is 255.

7. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In step S1, the grayscale value of the geometric mask area in the hybrid hologram follows an inverse Gaussian intensity distribution.

8. The method for controlling the shape and quality of a laser beam according to claim 1, characterized in that: In step S2, the angle α1 of the polarizer is 0°, and the angle α2 between the analyzer and the polarizer is 0° or 90°; In step S5, the first 4f system is composed of a first lens and a second lens, the focal length of the first lens is 1000 mm, and the focal length of the second lens is 30 mm; The second 4f system is composed of a first lens and a third lens, and the focal length of the third lens is equal to that of the first lens.

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