Pump laser beam homogenizing and laser amplifying device

Abstract

A homogenized pumping laser beam and laser amplification device belongs to the technical field of laser equipment and comprises a pumping beam combining unit module, a beam shaping subsystem, a collimating lens and a laser resonant cavity subsystem. The pumping beam combining unit module, the beam shaping subsystem, the collimating lens and the laser resonant cavity subsystem are installed together, the pumping beam combining unit module comprises a pumping laser subsystem and a beam combining station, the beam combining station is composed of a multi-face reflecting mirror and at least two focusing reflecting mirrors, the beam shaping subsystem comprises a micro-lens array with a plurality of lenses and a light mixing module, and the micro-lens array is composed of a plurality of lenses. A diaphragm is arranged between the micro-lens array and the multi-surface reflecting mirror; each pump laser subsystem includes a plurality of laser diode pump modules. According to the invention, the light beam can be effectively homogenized under the condition that the number of the pumping modules is small, even if a non-light-beam radiation area exists in the pumping light beam, sufficient homogenization is realized, the stability of a pumping laser subsystem and the like is improved, and the replacement process of the pumping modules is simplified.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a homogenized pumped laser beam and a laser amplification device. Background Technology

[0002] Laser systems (such as high-power solid-state lasers used in sheet metal welding and cutting) require appropriately designed pump power, i.e., the power of the pump modules (the pump modules emit laser light to irradiate the disk gain medium to excite the laser), to couple to the gain medium used for amplification in order to operate stably and reliably. In existing technologies, to obtain high pump power, the laser radiation from multiple pump modules can be coupled into a single pump laser beam within a mixing element. Furthermore, this superimposed pump beam can pass through a crystal multiple times within a designed resonant cavity, such as the disk gain medium used in disk laser amplifiers. The pump laser can generate laser light based on high-power diode laser modules, each containing multiple laser diode bars. Before coupling the pump laser beam to the laser gain medium of the laser system, the output radiation from different pump modules, i.e., different laser bars, can be homogenized in the mixing element to make the output pump laser beam profile more uniform.

[0003] To achieve scalability of the pump power of a laser system, it means that the system can be compatible with different numbers of pump modules. With the rest of the system structure remaining the same, the number of pump modules used can be adjusted according to the specific application. For example, if higher power is required, one or more pump modules need to be added. However, if a lower power is required, the number of pump modules is reduced, and the numerical aperture of the pump laser beam coupled to the mixing element will shrink. This results in the pump laser beam not being fully homogenized or not achieving the homogenization level required by the application. Specifically, the beam with a low numerical aperture does not reflect enough times in the homogenizer, and the light cannot be fully mixed. This situation may increase the sensitivity of the laser system (such as the amplification subsystem of the laser system) to the calibration status of the pump laser beam. Specifically, it manifests as increased sensitivity to changes in the optical path and / or intensity distribution, resulting in increased calibration difficulty and instability of the laser system, leading to the overall equipment being unable to operate stably and reliably. Besides the homogenization problem of pump laser caused by changing the number of pump modules mentioned above, another situation is that the power distribution of the pump beam will change when the pump module is replaced. This is because the new pump module usually has slightly different light output characteristics, especially slightly different beam angle distribution. If the numerical aperture of the focused pump light is too small, the homogenization effect achieved by the mixing element may be insufficient. Therefore, different pump modules may lead to different power distributions, and each distribution has varying degrees of deficiencies, which in turn leads to overall system instability or the need for recalibration. Summary of the Invention

[0004] To overcome the drawbacks of existing laser systems due to structural limitations, as described in the background art, this invention provides a pump beam combining unit module that can be adapted to different numbers of pump modules under the joint action of related mechanisms. The beam shaping subsystem is used to achieve beam homogenization and can effectively homogenize the beam even when the number of pump modules is small. Even when there are areas without beam radiation in the pump beam, sufficient homogenization should be achieved, which improves the stability of the pump laser subsystem and simplifies the pump module replacement process. This invention provides a homogenized pump laser beam and laser amplification device.

[0005] The technical solution adopted by this invention to solve its technical problem is: A homogenized pumped laser beam and laser amplification device includes a pump beam combining unit module, a beam shaping subsystem, a collimating lens, and a laser resonant cavity subsystem. The pump beam combining unit module includes a pump laser subsystem and a beam combining station. Multiple pump laser subsystems are installed at the rear end of the beam combining station, which consists of a multi-faceted mirror and at least two focusing mirrors, with the two focusing mirrors installed at the rear end of the multi-faceted mirror. The beam shaping subsystem is installed at the front end of the beam combining station, as are the collimating lens and the laser resonant cavity system. The beam shaping subsystem includes a microlens array with multiple lenses and a mixing module. The mixing module is installed at the front end of the microlens array, and an aperture is installed between the microlens array and the multi-faceted mirror. Each pump laser subsystem includes multiple laser diode pumping modules.

[0006] Furthermore, the pump beam combining unit module can superimpose multiple laser beams to form a primary pump laser beam. The beam shaping subsystem homogenizes the primary pump laser beam. After passing through the microlens array, the primary pump laser beam passes through the mixing module. The mixing module guides the primary pump laser beam through multiple reflections and outputs a homogenized pump laser beam.

[0007] Furthermore, the pump laser subsystem has at least four components, each of which emits multiple laser beams. The multiple laser beams pass through a beam combiner to form a pump beam. The beam combiner guides the pump beam to a focusing mirror via a multi-faceted mirror. The beam is then focused twice by two focusing mirrors to a suitable beam size before reaching the microlens array for homogenization.

[0008] Furthermore, the light mixing module is provided with an incident surface and an exit surface, and a microlens array of multiple lenses is installed on the incident surface of the light mixing module; the microlens array is an array of cylindrical lenses, and the cylindrical lenses are arranged along the fast axis direction to achieve focusing; the aperture is used to limit the beam size.

[0009] Furthermore, the light mixing module is a light homogenizing rod, which transmits the light beam from its own incident surface to the exit surface through multiple internal total internal reflections. The number of reflections of the light beam in the light homogenizing rod depends on the incident angle of each light beam towards the incident surface, thereby forming a uniform distribution of the exit light beam at the exit surface.

[0010] Furthermore, the length of the homogenizing rod and the number of microlenses through which the pump laser beam passes are designed as follows: when the microlens array is used in conjunction with the set minimum number of pump modules, the intensity fluctuation in the homogenized pump laser beam is less than 15%; the numerical aperture of the microlens array is matched with the divergence angle of the pump laser beam.

[0011] Furthermore, the plurality of laser diode pump modules are arranged adjacent to each other along the fast axis direction, and there is a gap between the primary pump laser beams formed by each laser diode pump module. The laser radiation generated by the laser diode pump modules is aligned side by side through optical elements.

[0012] Furthermore, each laser diode pump module has multiple diode strips for emitting laser beams. In the primary pump laser beam, the laser beams emitted by the diodes of one laser diode pump module are spaced apart along the fast axis of the diode strips. The multi-faceted reflector of the beam combiner station enables the laser radiation from the diode strips of different laser diode pump modules to be superimposed to form the primary pump laser beam. Furthermore, the laser resonant cavity subsystem is provided with a laser active medium to be pumped, and the homogenized pump laser beam generated by the pump beam combining unit module can irradiate the light-receiving surface of the laser active medium through the beam shaping subsystem.

[0013] Furthermore, during the process of the homogenized pump laser beam irradiating the laser-active medium multiple times, the homogenized pump laser beam will rotate.

[0014] Compared with existing technologies, the beneficial effects of this invention are as follows: The pump beam combining unit module in this invention can be adapted to different numbers of pump modules (pump laser subsystems). The beam shaping subsystem is used to achieve beam homogenization and should be able to effectively homogenize the beam even with a small number of pump modules. Even when there are areas without beam radiation in the pump beam, it can achieve a more uniform beam distribution effect regardless of angular space, improving the stability of the pump laser subsystem and laser amplifier system, and simplifying the pump module replacement process. When applied to end-use applications, it can improve the startup characteristics of disk laser systems, thereby helping to achieve a more stable and efficient operating state for disk laser systems. In summary, this invention has good application prospects. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] Figure 1 This is a schematic diagram of the structure of the present invention.

[0017] Figure 2 This is a partial structural schematic diagram of the present invention. Detailed Implementation

[0018] Figure 1 , 2 As shown, a homogenized pumped laser beam and laser amplification device includes a pump beam combining unit module, a beam shaping subsystem 2, a collimating lens 3, and a laser resonant cavity subsystem 4. The pump beam combining unit module includes a pump laser subsystem 101 and a beam combining station 102 (used to superimpose multiple laser beams to form a primary pump laser beam). There are four pump laser subsystems 101, which are installed at the rear end of the beam combining station 102. The beam combining station 102 uses an octagonal mirror 1021 to guide the pump beam to a focusing mirror, which focuses the beam twice to a suitable size to reach the micro-lens. The system consists of a mirror array for homogenization and two focusing mirrors 1022 (which receive the pump laser from the beam combiner, compress it horizontally and vertically, and reflect it towards the homogenizing plate; its structure is a spherical or aspherical mirror with a rectangular outline, bonded to a mechanical component with UV adhesive; this mechanical component is an optically flexible mechanical component that can adjust the direction of the mirror). The two focusing mirrors 1022 are mounted at the rear end of the octagonal mirror 1021; the beam shaping subsystem 2 is mounted at the front end of the beam combiner 102, the collimating lens 3 is mounted at the front end of the beam shaping subsystem 2, and the laser resonant cavity subsystem 4... The beam shaping subsystem 2 includes a microlens array 21 (each microlens is a rectangular quartz glass plate, one side of which is planar and the other side is a lens array of multiple semi-cylindrical columns) and a beam mixing module 23 (which guides the primary pump laser beam through multiple reflections and outputs a homogenized pump laser beam). The beam mixing module 23 is installed at the front end of the microlens array 21. An aperture 22 (a rectangular copper plate with square and round holes, which is adjusted by pressing a tube) is installed between the microlens array 21 and the octagonal mirror 1021. Cooling is used to filter stray light from the pump module; each pump laser subsystem 101 includes multiple laser diode pump modules, and each of the multiple pump modules corresponds to a laser beam region. Before superposition, two adjacent laser beam regions are arranged adjacent to each other in the primary pump laser beam along the fast axis (the pump module can be understood as a sealed hollow square shell with multiple light-emitting chips distributed inside, which can emit a nearly long elliptical pump laser with a certain divergence angle. The direction with a relatively large divergence angle in the vertical direction and good beam quality is called the fast axis).

[0019] Figure 1 , 2As shown, the pump beam combining unit module can superimpose multiple laser beams to form a primary pump laser beam (the advantage of superposition is that different numbers of pump modules can be selected as needed, thereby determining the actual pump laser power of the pump source as needed. In addition, the advantage of superimposing the pump beams of multiple pump modules is that the power requirements of a single pump module and the number and heat of the light-emitting chips can be reduced, thereby extending the lifespan of the light-emitting chips in a single pump module). The beam shaping subsystem can homogenize the primary pump laser beam. After passing through the microlens array 21, the primary pump laser beam passes through the mixing module. The mixing module guides the primary pump laser beam through multiple reflections and outputs a homogenized pump laser beam through the collimating lens 3 (the goal of homogenization is to output a pump laser spot with a consistent laser power distribution and shape, which is also more uniform when absorbed by the crystal in the rear resonant cavity without obvious power gradient distribution, thus making the heating on the resonant cavity crystal more uniform). There are at least four pump laser subsystems 101, each emitting multiple laser beams. These beams are combined by a beam combiner to form a pump beam. The beam combiner guides the pump beam to a focusing mirror 1022 via at least eight mirrors 1021. The beam is then focused twice by two focusing mirrors 1022 to a suitable size before reaching the microlens array 21 for homogenization. The beam mixing module has an incident surface and an exit surface. The microlens array 21, consisting of multiple lenses, is mounted on the incident surface of the beam mixing module or near it. The microlens array 21 is an array of cylindrical lenses arranged along the fast axis to achieve focusing (its function is to compress the homogenized spot again and focus it onto the incident end face of the octagonal prism homogenizing rod). An aperture 22 is used to limit the beam size. The beam mixing module 23 is a homogenizing rod that guides the light beam from its incident surface to the exit surface through multiple internal total internal reflections. The number of reflections of the beam in the homogenizing rod 23 depends on the incident angle of each beam hitting the incident surface, thereby creating a uniform distribution of the exit beam at the exit surface. The length of the homogenizing rod 23 and the number of pump laser beams passing through the microlenses are designed as follows: when the microlens array is used in conjunction with the minimum set number of pump modules, the intensity fluctuation in the homogenized pump laser beam is less than 15%; the numerical aperture of the microlens array 21 is matched with the divergence angle of the pump laser beam (the divergence angle is matched by selecting the refractive index of the glass substrate of the homogenizing rod, the size of the incident end face, and the distance of the incident end face from the homogenizer, so that the pump laser with a certain divergence angle emitted from the homogenizer can all enter the homogenizing rod without total internal reflection at the incident end face). Four laser diode pump modules are arranged adjacent to each other along the fast axis. There is a gap between the primary pump laser beams formed by each laser diode pump module. The laser radiation generated by the laser diode pump modules is aligned side by side through optical elements (which can be understood as the light-emitting surfaces of the light-emitting chips are arranged in a gap facing one direction, and the lasers of multiple chips can be directly combined into one beam after being reflected by a mirror).Each laser diode pump module has multiple diode strips for emitting the laser beam. In the primary pump laser beam, the laser beams emitted by the diodes of one laser diode pump module are spaced apart along the fast axis of the diode strips. The multifaceted reflector 1021 of the beam combiner station allows the laser radiation from the diode strips of different laser diode pump modules to be superimposed to form the primary pump laser beam. The laser resonant cavity subsystem 4 is equipped with a laser-active medium to be pumped (its main function is to absorb the pump laser and then excite the laser through electronic energy level transitions). The homogenized pump laser beam generated by the pump combining unit module can irradiate the light-receiving surface of the laser-active medium. After the photons in the homogenized pump laser beam are absorbed by the laser crystal, the electrons in the laser crystal absorb energy and jump from a low energy state to a high energy state and remain in the high energy state (statistically, the distribution of electron states in the low energy state is less than that in the high energy state, that is, energy state inversion occurs, and energy state inversion is a basic condition for laser excitation).

[0020] Figure 1 , 2 As shown, the beam shaping subsystem 2 also has an amplification unit submodule, which includes a gain medium and a disk amplifier. In practical applications, the wavelength of the pump laser subsystem 101 needs to match the pump light characteristics required by the disk crystal within the laser cavity (the laser cavity refers to the laser resonant cavity after the pump source, generally referring to a conventional FP resonant cavity or a multi-pump resonant cavity of a disk laser; a typical structure of the resonant cavity is two mirrors with a laser crystal in the middle). A pump module consists of multiple laser bars, each bar composed of multiple laser diodes arranged in a stacked manner with spacing between them, along the fast axis of the output beam. The output beam is as follows: Figure 1 The laser intensity distribution diagram shown in Figure 103 illustrates this; a single elliptical spot is generated by a diode bar corresponding to the pump module, and after combination, a primary pump laser beam with a rectangular cross-section can be obtained. Multiple pump modules can be used. Figure 1 This describes four pump modules. The beams emitted by these four pump modules are reflected by eight mirrors 1021 arranged at intervals in the beam combiner station 102 onto the first focusing mirror 1022, forming a beam like... Figure 1The cross-sectional distribution of the light spot shown in Figure 104 is obtained by combining the beam into a single spot through two reflecting focusing mirrors. Then, the mixing element is placed in a suitable position on the second reflecting focusing mirror to shape and homogenize the light spot. In order to ensure the homogenization effect of the laser beam (the compressed pump laser beam from the reflecting mirror 2), the following conditions should be met as much as possible: (1) The cylindrical microlens array 21 is placed close to the entrance of the homogenizing rod 23, and it is necessary to ensure that the pump laser beam passes through at least five cylindrical lenses 21 to ensure that the homogenizing rod 23 can effectively mix the light. (2) The width of each cylindrical microlens 21 must be less than 1 / 5 of the entrance width of the light homogenizing rod 23 in order to obtain a sufficient number of spatial sampling points (i.e., the number of sub-light sources). The above can be understood as the smaller the width, the greater the density of light homogenization. The light homogenizing rod is composed of many small semi-circular strip focusing lenses. Their adjacent arrangement can cut the incident light plate into more long light spots and then refocus and compress it into a finer and shorter linear light spot. The finer the semi-circular strip focusing lens on the light homogenizing rod, the more light spots can be cut into, i.e., the more spatial sampling points there are, and the finer the linear light spot in the refocused and compressed light spot. (3) Based on the focal length f of the microlens array 21 and the offset / spacing p between adjacent lenses (for cylindrical lenses, the offset in the curvature direction), the numerical aperture of the microlens array 21 can be determined: NA_microlens array = p / (2f). In this way, multiple parallel "new light sources" with specific angular distribution can be created at the entrance of the homogenizing rod 23, thereby greatly improving the homogenization effect. The design principle of the homogenizing rod 23 is that the incident light is reflected multiple times through the incident surface of the homogenizing rod 23 to the exit surface of the homogenizing rod. The number of reflections of the beam in the homogenizing rod usually depends on the incident angle of the corresponding beam, thereby forming a uniform (or more uniform) distribution of the exit beam on the exit surface. The cross-sectional area of ​​the homogenizing rod depends on different applications and can be rectangular, hexagonal or octagonal. Figure 1Figure 105 shows the intensity distribution of the homogenized octagonal spot. When the pump laser subsystem is configured to accommodate different numbers of pump modules, the design conditions for the length of the homogenizing rod and the number of cylindrical lenses through which the light is transmitted are such that when used with the minimum set number of pump modules in conjunction with the mixing element, the intensity fluctuation of the homogenized pump laser beam is less than 15%. After the pump beam is homogenized by the mixing element 23 (mixing module), it can be applied to a laser amplification system, such as the laser resonator subsystem 4 of a disk laser amplification system. The homogenized pump laser is collimated by a lens, then focused by a parabolic mirror, and then illuminates the disk gain medium. After multiple reflections by the disk, prism, and parabolic mirror, the pump laser passes through the gain medium multiple times and is absorbed multiple times. The parabolic mirror has a central opening, and the laser generated by stimulated emission from the gain medium exits through this central opening. In addition, homogenized pumped laser beam devices can also be used in laser amplification systems that use slab or columnar crystals as the gain medium, or for optical pumping of semiconductor lasers (typically in continuous and pulsed applications).

[0021] Figure 1 , 2 As shown, through all the above technical solutions, in this invention, the pump beam combining unit module can be adapted to different numbers of pump modules (pump laser subsystems), and the beam shaping subsystem is used to achieve beam homogenization. It should be able to effectively homogenize the beam even when the number of pump modules is small. Even when there are no beam radiation areas in the pump beam, it can achieve a beam distribution effect with better uniformity without depending on the angular space, thereby improving the stability of the pump laser subsystem and the laser amplifier system and simplifying the pump module replacement process. When applied to end-use applications, it can improve the startup characteristics (e.g., transient response speed and stability) of disk laser systems, thereby helping to achieve a more stable and efficient operating state for disk laser systems, etc.

[0022] Those skilled in the art should understand that although this specification describes embodiments, the embodiments do not necessarily contain only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. Therefore, the scope of protection of this application is defined by the claims.

Claims

1. A homogenized pump laser beam and laser amplification device, comprising a pump beam combining unit module, a beam shaping subsystem, a collimating lens, a laser resonator cavity subsystem; characterized in that, The pump beam combining unit module comprises pump laser subsystems, a beam combining station, the pump laser subsystems are multiple, the multiple pump laser subsystems are installed at the rear side end of the beam combining station, the beam combining station is composed of a plurality of reflecting mirrors and at least two focusing mirrors, the two focusing mirrors are installed at the rear end of the eight reflecting mirrors; the beam shaping subsystem is installed at the front side end of the beam combining station, a collimating lens is installed at the front side end of the beam shaping subsystem, and a laser resonant cavity subsystem is installed at the front side end of the collimating lens; the beam shaping subsystem comprises a microlens array with multiple lenses and a light mixing module, the light mixing module is installed at the front side end of the microlens array, and a diaphragm is installed between the microlens array and the plurality of reflecting mirrors; each pump laser subsystem comprises multiple laser diode pumping modules.

2. A homogenized pump beam and laser amplification device as claimed in claim 1, wherein, The pump beam combining unit module can superimpose multiple laser beams to form a primary pump laser beam, the beam shaping subsystem homogenizes the primary pump laser beam, the primary pump laser beam passes through the microlens array and then passes through the light mixing module, the light mixing module reflects and guides the primary pump laser beam multiple times and outputs a homogenized pump laser beam.

3. A homogenized pump beam and laser amplification device as claimed in claim 1, wherein, The pump laser subsystems are at least four, each pump laser subsystem emits multiple laser beams, and the multiple laser beams pass through the beam combining station to form a pump beam; the beam combining station guides the pump beam to the focusing mirror through the plurality of reflecting mirrors, and the pump beam is focused twice by the two focusing mirrors to a suitable beam size to reach the microlens array for homogenization.

4. The homogenized pump beam and laser amplification device of claim 1, wherein, The light mixing module is provided with an incident surface and an exit surface, and the microlens array with multiple lenses is installed on the incident surface of the light mixing module; the microlens array is an array of cylindrical lenses arranged along the fast axis direction to achieve focusing; and the diaphragm is used to limit the beam size.

5. The homogenized pump beam and laser amplification device of claim 1, wherein, The light mixing module is a light homogenizing rod, which conducts the light beams from the incident surface to the exit surface through multiple internal total reflections, and the number of reflections of the light beams in the light homogenizing rod depends on the incident angle of each light beam on the incident surface, so that a uniform distribution of the exit light beams is formed at the exit surface.

6. A homogenized pump beam and laser amplification device as claimed in claim 1, wherein, The length of the light homogenizing rod and the number of microlenses through which the pump laser beam passes are designed as follows: when the microlens array is combined with the minimum number of pump modules set, the intensity fluctuation in the homogenized pump laser beam is less than 15%; and the numerical aperture of the microlens array is matched with the divergence angle of the pump laser beam.

7. The homogenized pump beam and laser amplification device of claim 1, wherein, The multiple laser diode pumping modules are arranged adjacent to each other along the fast axis direction, and there is a gap between the primary pump laser beams formed by each laser diode pumping module, wherein the laser radiation generated by the laser diode pumping modules is aligned side by side through optical elements.

8. The homogenized pump beam and laser amplification device of claim 1, wherein, Each laser diode pumping module has multiple diode bars for emitting laser beams, wherein in the primary pump laser beam, the laser beams emitted by the diodes of one laser diode pumping module are arranged in a spaced manner along the fast axis direction of the diode bar; and the plurality of reflecting mirrors of the beam combining station can superimpose the laser radiation of the diode bars of different laser diode pumping modules to form the primary pump laser beam.

9. The homogenized pump beam and laser amplification device of claim 1, wherein, The laser resonant cavity subsystem is provided with a laser active medium to be pumped, and the homogenized pump laser beam generated by the pump beam combining unit module can irradiate the light receiving surface of the laser active medium through the beam shaping subsystem.

10. The homogenized pump beam and laser amplification device of claim 1, wherein, During the process that the homogenized pump laser beam irradiates the laser active medium continuously for multiple times, the homogenized pump laser beam will rotate.

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