Laser beam shaping device and disc laser

Abstract

The present disclosure provides a beam shaping device for a laser and a laser module comprising the same, in one embodiment, the shaping device may comprise: a collimation module for forming an input pump beam into collimated light; the shaping module is used for shaping the beam in the meridian direction and the beam in the sagittal direction of the collimated light; and the focusing module is used for focusing the shaped light beams in the meridian direction and the sagittal direction to form flat-topped light spots. The shaping device provided by the utility model can be suitable for off-axis laser beam shaping, and can form a flat-topped beam on the disc-type gain medium.

Description

A laser beam shaping device and a disk laser Technical Field

[0001] This application relates generally to the field of laser technology, and in particular to a beam shaping device and laser module applicable to disk lasers. Background Technology

[0002] Laser technology has been widely applied in many fields such as communications, medicine, and materials processing. Based on their operating mode, lasers can be divided into continuous lasers and pulsed lasers. Among them, pulsed lasers, due to their high power and high precision, have broad application prospects in circuit manufacturing, wafer dicing, laser surgery, and fiber optic communications. Disk lasers play an important role in the generation of high-power, high-energy ultrashort pulse lasers because they can significantly reduce the thermal effects in the laser gain medium.

[0003] In recent years, high-power ultrashort pulse lasers have demonstrated immense value in scientific research and commercial fields such as optical frequency combs and high-order harmonic generation. This has placed higher demands on disk lasers, a key pumping method. How to obtain output lasers with higher energy and better beam quality has become a problem that needs to be solved.

[0004] Currently, the pump source laser used in multi-stroke disk laser head modules is often first introduced off-axis into the disk gain medium through a parabolic mirror. The greater the off-axis offset, the more severe the degradation of the beam uniformity, which greatly affects the beam spot excited by the final multi-stroke pump. Existing solutions also propose a method to pre-shape the beam into an elliptical spot using a non-spherical symmetric homogenizer, but these methods are difficult to guarantee stable and reliable operation at high power. Summary of the Invention

[0005] To address the aforementioned problems, this application is proposed. Embodiments of this application provide laser beam shaping that can be used off-axis, enabling uniform beam output from, for example, multi-stroke disk lasers.

[0006] According to an exemplary embodiment, a laser beam shaping device is provided, characterized in that it includes: a collimation module for forming an input pump beam into collimated light; a shaping module for shaping the meridional beam and the sagittal beam of the collimated light; and a focusing module for focusing the shaped meridional and sagittal beams to form a flat-topped light spot.

[0007] In some embodiments, the collimation module includes a collimating lens, the numerical aperture of which is larger than the numerical aperture of the input pump beam.

[0008] In some embodiments, the shaping module includes a spherical mirror and a hybrid cylindrical mirror disposed along the beam direction, wherein the spherical mirror is used to adjust the beam size of the collimated light in the meridional and sagittal directions, and the hybrid cylindrical mirror is used to adjust the size of the meridional beam relative to the sagittal beam, so as to form a flat-topped spot on the focal plane of the focusing module.

[0009] In some embodiments, the hybrid cylindrical lens includes a first cylindrical lens and a second cylindrical lens, wherein the first cylindrical lens and the second cylindrical lens are located within the same lens.

[0010] In some embodiments, the first cylindrical mirror has a meridional optical power characteristic, and the second cylindrical mirror has a sagittal optical power characteristic, such that the light beam, after passing through the spherical mirror and the first cylindrical mirror, forms a collimated beam in the meridional direction, and after passing through the spherical mirror and the second cylindrical mirror, forms a collimated beam in the sagittal direction.

[0011] In some embodiments, the spherical mirror is a positive lens, and the first and second cylindrical mirrors of the hybrid cylindrical mirror are negative cylindrical mirrors; or, the spherical mirror is a negative lens, and the first and second cylindrical mirrors of the hybrid cylindrical mirror are positive cylindrical mirrors.

[0012] In some embodiments, the hybrid cylindrical mirror is located between the focal points of the spherical mirror and the spherical mirror.

[0013] In some embodiments, the focusing module is a parabolic reflector.

[0014] In some embodiments, the collimation module, the shaping module, and the focusing module are made of one or more of fused silica, titanate glass, and borosilicate glass.

[0015] In some embodiments, the flat-top light spot is a symmetrical circular light spot.

[0016] According to an exemplary embodiment, a laser module is also provided, characterized in that it includes: a pump source for outputting a pump beam; the aforementioned laser beam shaping device for converting the pump beam into a flat-topped pump spot; and a disk-type gain medium that receives the energy of the pump spot and generates laser light.

[0017] Based on some implementation methods, the beam shaping apparatus of this application, by separating the beam shaping in both meridional and sagittal directions and combining it with beam focusing operations, can obtain a uniform spot on the focal plane, forming a symmetrical flat-top laser. The beam shaping apparatus and method of this application have wide applicability; for example, they can be applied to off-axis laser beam shaping and pump source beam shaping of multi-stroke disk laser head modules. They can effectively correct the spot degradation introduced by off-axis operation, forming a flat-top beam on the disk gain medium, thereby ensuring stable and reliable operation of the laser system at high power.

[0018] The above and other features and advantages of this invention will become apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. It should be understood that the exemplary embodiments do not necessarily achieve all of these advantages. Therefore, this invention may be embodied or implemented in a manner that achieves or optimizes one or more advantages as taught herein, without necessarily achieving the other advantages as taught or demonstrated herein. Attached Figure Description

[0019] Figure 1 shows a schematic diagram of the pump spot according to the prior art;

[0020] Figure 2 shows a schematic diagram of the overall structure of a shaping device according to an embodiment of this application;

[0021] Figure 3 shows a schematic diagram of the specific structure of a shaping device according to an embodiment of this application;

[0022] Figures 4A-4C show schematic diagrams of the structure of a hybrid cylindrical mirror according to an embodiment of this application;

[0023] Figure 5 shows a schematic diagram of the spot on the disk gain medium after the pump spot has been shaped using the shaping device according to an embodiment of this application.

[0024] The names of the corresponding components indicated by the reference numerals in the figure are as follows:

[0025] 10 - Pump source, 110 - Collimating lens, 122 - Spherical mirror, 124 - Hybrid cylindrical mirror, 130 - Parabolic mirror, 20 - Disk gain medium. Detailed Implementation

[0026] Exemplary embodiments of this application are described below with reference to the accompanying drawings. It is obvious that the described embodiments are merely a portion of the embodiments of this application, and not all of them. In the drawings, the same reference numerals generally represent the same parts. It should be understood that the dimensions and sizes of the parts shown in the drawings are not necessarily drawn to scale, and they may differ from those shown herein for implementation. Furthermore, some embodiments may combine any suitable combination of features from two or more of the drawings.

[0027] As described in the background section, for multi-stroke disk laser head modules, the pump source laser typically needs to be introduced off-axis into the disk gain medium, which leads to degradation of the light wave uniformity. Figure 1 shows a schematic diagram of the pump spot in the prior art, where the left image shows the degraded pump laser spot after a single stroke, and the right image shows the spot after multi-stroke pumping. It can be seen that the degraded spot after a single stroke is elliptical, while the final output spot after multi-stroke pumping is roughly circular due to the superposition effect. However, the energy distribution in the X and Y directions is uneven, the edge energy attenuation is inconsistent, the flat-top effect is poor, and the spot's circularity is not ideal. This non-uniform high-power pump spot leads to irregular surface shape caused by thermal effects and soft aperture superposition. The spot excited by multi-stroke superposition will also degrade, and severe surface shape changes may even cause crystal fragmentation.

[0028] To address this technical problem, embodiments of this application provide a laser beam shaping apparatus and method. Figure 1 shows a schematic diagram of the overall structure of a laser shaping apparatus according to an embodiment of this application. As shown in Figure 1, the laser shaping apparatus may include a collimation module 110, a shaping module 120, and a focusing module 130. The collimation module 110 can receive pump light output from a pump source 10 (e.g., a semiconductor laser) and shape the input pump beam into collimated light. The shaping module 120 is coaxially arranged with the collimation module 110 (i.e., along the optical axis of the pump beam), receives the collimated beam, and shapes the meridional and sagittal beams of the collimated beam. The focusing module 130 can be off-axis arranged with the shaping module 110 and the collimation module, and focuses the shaped beam (including the meridional and sagittal beams) to form a flat-topped spot. The energy of this flat-topped pump spot can be received and absorbed by a laser gain medium 20 disposed at the focal plane to generate laser light.

[0029] The technical solution of this application embodiment can be applied to the pump source beam shaping of a multi-stroke disk laser head module. By separating the beam shaping in the meridional and sagittal directions and combining it with the characteristics of the focusing module, it can correct the spot degradation caused by off-axis, and achieve a uniform spot at the focal plane, thereby ensuring the stable and reliable operation of the laser system at high power.

[0030] The following describes some specific embodiments of the present invention through the specific structure of the shaping device. However, it should be understood that this description only shows the preferred solution of the present invention and is not a limitation on the implementation of the present invention.

[0031] Figure 3 shows a schematic diagram of a shaping device applicable to a disk laser system according to an embodiment of this application, and also illustrates a single-stroke pump optical path. As described in detail below, the disk laser module shown in Figure 3 generally includes a pump source, a shaping device, and a laser output module.

[0032] Pump source 10 is used to output pump light, and can be selected from pulsed semiconductor lasers, solid-state lasers, etc. The wavelength of the pump light generated by the pump source is within the absorption spectrum range of the laser gain medium 20, for example, 700-1500 nm, preferably 800-1000 nm. In one example, the beam emitted from pump source 10 is a circularly distributed Gaussian beam. It is understood that this is merely an example, and the beam is not limited to a Gaussian distribution; for example, it could also be an Airy distribution.

[0033] The shaping device includes a collimation module 110, a shaping module 120, and a focusing module 130. The collimation module 110 includes a collimating lens for collimating the input pump light into a parallel beam. In one example, the numerical aperture (NA) of the collimating lens 110 is larger than the numerical aperture of the input pump beam (i.e., the output spot of the pump source 10), thus allowing for a larger margin in mounting the collimating lens relative to the pump source and enabling optical coupling of all pump light energy. In this sense, the pump source 10 and the collimating lens can be considered to together constitute the collimation module 110. As shown in the figure, in one example, the beam output from the collimating lens to the subsequent shaping module 120 is an extended beam, which also satisfies a Gaussian distribution or other optical distribution.

[0034] Referring to Figures 1 and 3, the shaping module 120 of this embodiment includes two parts arranged along the beam direction: a spherical mirror 122 and a hybrid cylindrical mirror 124. The collimated beam passes sequentially through the spherical mirror 122 and the hybrid cylindrical mirror 124. The spherical mirror 122 can be used to adjust the beam size of the input collimated light in the meridional and sagittal directions, and the hybrid cylindrical mirror 124 can be used to adjust the size of the meridional beam relative to the sagittal beam (or, in other words, adjust the size of the sagittal beam relative to the meridional beam), thereby forming a flat-topped spot at the focal plane of the subsequent focusing module 130.

[0035] In one embodiment, the collimated light can be incident orthogonally onto the spherical mirror 122, thus ensuring that the size of the adjusted beam is equivalent or substantially the same in the meridional and sagittal directions. The spherical mirror 122 can be a positive or negative lens, such as a plano-convex or biconvex positive lens, or a plano-concave or biconcave negative lens. Preferably, when the shaping module 120 is used for beam expansion and shaping, the lens 122 is a positive lens (correspondingly, the lens 124 can be a negative cylindrical mirror for collimation); when the shaping module 120 is used for beam contraction and shaping, the lens 122 is a negative lens (correspondingly, the lens 124 can be a positive cylindrical mirror for collimation).

[0036] Typically, as shown in Figure 3, the shaping module 120 is used for beam expansion and shaping. For example, it positions the hybrid cylindrical lens 124 between the spherical lens 122 and its focal point, and the size of the final output beam spot can be adjusted by controlling the size of the beam converged at the lens 124 through adjusting the position of the hybrid cylindrical lens 124 relative to the spherical lens 122. In one example, the focal length of the spherical lens 122 is 50-100mm, and the distance between the hybrid cylindrical lens 124 and the spherical lens 122 is 15-40mm. This distance is adjustable to first converge the beam to a suitable size, and then collimate and expand the beam through the hybrid cylindrical lens 124.

[0037] In this text, "hybrid cylindrical mirror" means that the cylindrical mirror comprises multiple cylindrical surfaces or is composed of multiple cylindrical mirrors. These multiple cylindrical surfaces or cylindrical mirrors can be used to shape the beam in the meridional and sagittal directions, thereby adjusting the overall size of the meridional beam relative to the sagittal beam, and simultaneously adjusting the phase of the beam for homogenization. In one example, the hybrid cylindrical mirror 124 may include a first cylindrical mirror and a second cylindrical mirror arranged sequentially, with the beam incident on the first cylindrical mirror and the second cylindrical mirror sequentially. In this way, the hybrid cylindrical mirror 124 can achieve separate shaping of the beam in the meridional and sagittal directions. For example, the first cylindrical mirror has a meridional (YZ direction) optical power characteristic, that is, it at least collimates the beam in the meridional direction, but may not have a shaping effect on the beam in the sagittal direction. The second cylindrical mirror has a sagittal (XZ direction) optical power characteristic, that is, it collimates the beam in the sagittal direction, but may not have a shaping effect on the beam in the meridional direction. Furthermore, the optical power characteristics of the two mirrors may be different. Thus, after passing through spherical mirror 122 and the first cylindrical mirror, the beam becomes a collimated beam in the meridional direction, and after passing through spherical mirror 122 and the second cylindrical mirror, the beam becomes a collimated beam in the sagittal direction. Alternatively, after passing through spherical mirror 122 and the first cylindrical mirror, the beam becomes a collimated beam in the sagittal direction, and after passing through spherical mirror 122 and the second cylindrical mirror, the beam becomes a collimated beam in the meridional direction. Here, "collimated" is intended to indicate that the divergence angle of the beam is reduced after shaping, and does not mean that an absolutely parallel beam is formed.

[0038] Figures 4A-4C show schematic diagrams of the structure of a hybrid cylindrical lens 124 according to an embodiment of this application. As shown in Figure 4A, the hybrid cylindrical lens 124 includes two cylindrical surfaces along the beam axis (Z-axis), or in other words, it includes two cylindrical mirrors, which are used to shape the meridional beam and the sagittal beam, respectively. Preferably, as shown, the two cylindrical mirrors are integrally formed within the same lens, thereby ensuring that component crosstalk is not introduced due to assembly and adjustment, and improving the shaping effect of the output beam spot. However, this application is not limited to this. In some examples, two separate lenses can also be used to form the cylindrical shaping part.

[0039] Figures 4B-4C show the front and oblique side views of the hybrid cylindrical mirror in Figure 4A. As shown, the hybrid cylindrical mirror 124 can be considered as composed of cylindrical mirror 124-1 and cylindrical mirror 124-2. The cross-sections (XY planes) of the two cylindrical mirrors are circular. Cylindrical mirror 124-1 has optical power characteristics in the YZ direction and can collimate the beam in the meridional direction. Cylindrical mirror 124-2 has optical power characteristics in the XZ direction and can collimate the beam in the sagittal direction. The beam first passes through cylindrical mirror 124-1 to form a collimated beam in the meridional direction, and then passes through cylindrical mirror 124-2 to form a collimated beam in the sagittal direction. The figures show that cylindrical mirror 124-1 and cylindrical mirror 124-2 are negative lenses (concave). Combined with Figure 3, they can form a beam expanding and shaping module with spherical mirror 122. It is understandable that when spherical mirror 122 is selected as a negative lens, cylindrical mirrors 124-1 and 124-2 can be positive cylindrical mirrors (convex surfaces) to achieve beam shaping. It is also understandable that the positions of cylindrical mirrors 124-2 and 124-1 can be changed, meaning the beam first passes through cylindrical mirror 124-2 and then through cylindrical mirror 124-1 for beam shaping.

[0040] In a preferred embodiment, the collimating lens 110, the spherical mirror 122, and the hybrid cylindrical mirror 124 may be made of one or more of fused silica, titanate glass, and borosilicate glass, including but not limited to optical glass such as ULE and BK7, which have a low coefficient of thermal expansion and can withstand high-power pump light.

[0041] Referring back to Figure 3, a focusing module 130 is positioned off-axis in the output optical path after the beam is shaped by a spherical mirror and a hybrid cylindrical mirror. This module can be a parabolic mirror, used to focus the beam and guide it to a disk-shaped gain medium 20 coaxial with the parabolic mirror. Similar to lenses 110, 122, and 124, the parabolic mirror 130 can also be made of materials such as fused silica, titanate glass, or borosilicate glass. As shown, the focused beam is obliquely incident onto the laser gain medium 20. The laser gain medium 20 is used to absorb pump light and provide gain to generate stimulated emission light. For example, it can be a laser crystal material, including but not limited to one or more of ytterbium-doped yttrium aluminum garnet (Yb:YAG), ytterbium-doped lutetium oxide (Yb:Lu2O3), or ytterbium-doped lutetium aluminum garnet (Yb:LuAG). In one embodiment, the laser gain medium 20 may have a disk shape with a diameter of, for example, 5-16 mm and a thickness of, for example, 0.2-1 mm, preferably less than 0.5 mm. The thin-film crystal has good axial heat dissipation capability, which is beneficial for stable operation. In one example, the input pump beam generates a large amount of waste heat when loaded onto the disk-shaped gain medium 20. To eliminate its adverse effects on optical devices, heat dissipation is required. Therefore, a heat sink or other heat dissipation device can be provided on the back of the disk-shaped gain medium 20, which can be used to support and fix the laser gain medium and absorb the heat generated by the laser gain medium during operation. For information on the heat sink and the arrangement of the disk-shaped crystal, please refer to the Chinese patent application CN 202520164712.0 of the inventors and applicant, the entire contents of which are incorporated herein by reference.

[0042] As described above, due to the separation and shaping of the pump beam in the meridional and sagittal directions, the embodiments of this application can achieve symmetrical flat-topped pump spots at 20 locations on the disk crystal during a single stroke. Figure 5 shows a schematic diagram of the single-stroke pump spot obtained after shaping the pump beam using the shaping device of this embodiment. As shown in the figure, the beam passes through lenses 122 and 124 and the parabolic mirror 130, resulting in a larger, uniform flat-topped spot. This spot is a symmetrical circular spot, and the energy is relatively uniform throughout the spot. Due to the existence of the disk crystal damage threshold, a larger uniform pump spot size is beneficial for high-power laser output and ensures stable system operation at high power.

[0043] Although Figure 3 only shows a single-stroke optical path, it can be understood that multi-stroke pumping can be achieved by setting a total internal reflection mirror (not shown). For example, the laser gain medium 20 receives part of the pump light energy and reflects the unabsorbed part. The total internal reflection mirrors on the reflection path (for example, one can be set above and one below the laser gain medium 20) can guide the reflected pump light back to the laser gain medium 20 and absorb the remaining energy of the pump light. After multi-stroke, the laser gain medium can generate laser light. At the same time, the parabolic mirror 130 (coated with a semi-transparent and semi-reflective film) and the laser gain medium 20 form a resonant cavity. The laser light generated after fully extracting energy is output through the parabolic mirror 130. That is, the parabolic mirror 130 also constitutes part of the laser output module.

[0044] An exemplary embodiment of this invention also provides a disk laser or optical system including the aforementioned laser beam shaping device. As described above, the shaping device can be used to convert a pump beam into a flat-topped pump spot. Besides the shaping device, it may also include components such as a pump source and a laser output module. The laser output module may include a disk-type gain medium, an output parabolic mirror, etc. (which can also be used as a focusing lens in the shaping device). This laser amplification device can be applied in fields such as circuit manufacturing, radar detection, and fiber optic communication.

[0045] The exemplary structure and composition of the laser beam shaping device of this application and the disk laser module including the device are described above with reference to FIG2-5. The beam shaping in the two directions of separation of meridional and sagittal is achieved by, for example, the shaping module. Combined with the beam focusing operation, the beam deterioration caused by off-axis can be corrected, and a uniform beam spot can be obtained on the focal plane to form a symmetrical flat-top laser. This helps the laser optical system to operate stably and reliably at high power.

[0046] It should be understood that although terms such as "first" or "second" may be used herein to describe different parts or features, these parts or features are not limited to these terms. The use of these terms distinguishes one part from another without emphasizing order, positional relationship, etc. For example, without departing from the scope of this disclosure, the first part may be referred to as the second part; and the second part may also be referred to as the first part. That is to say, modifiers without quantifiers, such as "first" and "second," are interchangeable.

[0047] In this text, words such as “including,” “contains,” and “has” are open-ended terms meaning “including but not limited to,” and are used interchangeably. The words “or” and “and” as used herein refer to the words “and / or” and are used interchangeably unless the context explicitly indicates otherwise. The word “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably.

[0048] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many combinations, modifications, and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of this application should be determined by the claims.

Claims

1. A laser beam shaping device, characterized in that, include: Collimation module, which is used to collimate the input pump beam; A shaping module is used to shape the meridional beam and the sagittal beam of the collimated light; And a focusing module, which is used to focus the shaped meridional and sagittal beams to form a flat-topped spot.

2. The laser beam shaping device as described in claim 1, characterized in that, The collimation module includes a collimating lens, the numerical aperture of which is larger than the numerical aperture of the input pump beam.

3. The laser beam shaping device as described in claim 1, characterized in that, The shaping module includes a spherical mirror and a hybrid cylindrical mirror arranged along the beam direction. The spherical mirror is used to adjust the beam size of the collimated light in the meridional and sagittal directions, and the hybrid cylindrical mirror is used to adjust the size of the meridional beam relative to the sagittal beam, so that a flat-topped spot is formed on the focal plane of the focusing module.

4. The laser beam shaping device as described in claim 3, characterized in that, The hybrid cylindrical lens includes a first cylindrical lens and a second cylindrical lens, which are located within the same lens.

5. The laser beam shaping device as described in claim 4, characterized in that, The first cylindrical mirror has a meridional optical power characteristic, and the second cylindrical mirror has a sagittal optical power characteristic, so that the light beam forms a collimated beam in the meridional direction after passing through the spherical mirror and the first cylindrical mirror, and forms a collimated beam in the sagittal direction after passing through the spherical mirror and the second cylindrical mirror.

6. The laser beam shaping device as described in claim 4, characterized in that, The spherical mirror is a positive lens, and the first and second cylindrical mirrors of the hybrid cylindrical mirror are negative cylindrical mirrors; or, the spherical mirror is a negative lens, and the first and second cylindrical mirrors of the hybrid cylindrical mirror are positive cylindrical mirrors.

7. The laser beam shaping device as described in claim 3, characterized in that, The hybrid cylindrical mirror is located between the focal points of the spherical mirror and the spherical mirror.

8. The laser beam shaping device as described in claim 1 or 2, characterized in that, The focusing module is a parabolic reflector.

9. The laser beam shaping device as described in claim 1 or 2, characterized in that, The flat-top light spot is a symmetrical circular light spot.

10. A disk laser, characterized in that, include: Pump source, used to output a pump beam; The laser beam shaping apparatus according to any one of claims 1-9 is used to convert the pump beam into a flat-topped pump spot; And a disk-type gain medium, which receives the energy of the pump spot and generates laser light.

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