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 invention can be suitable for off-axis laser beam shaping, and can form a flat-topped beam on the disc-type gain medium.

Description

Technical Field

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

[0002] Laser technology has been widely applied in many fields such as communication, medical treatment, and material processing. Classified by working mode, lasers can be divided into continuous lasers and pulsed lasers. Among them, pulsed lasers have broad application prospects in fields such as circuit manufacturing, wafer cutting, laser surgery, and optical fiber communication due to their high power and high precision characteristics. Disk lasers play an important role in the generation of high-power, high-energy ultrashort pulsed lasers because they can greatly reduce the thermal effect in the laser gain medium.

[0003] In recent years, high-power ultrashort pulsed lasers have demonstrated great value in scientific research and commercial fields such as optical frequency combs and high-harmonic generation, which pose relatively high requirements for disk lasers as key pumping means. How to obtain output lasers with higher energy and better beam quality has become a problem to be solved.

[0004] The pump source laser currently applied to multi-stroke disk laser head modules often first enters the disk gain medium off-axis through a parabolic mirror. The larger the off-axis offset, the more serious the deterioration of the spot uniformity, which has a great impact on the spot finally excited by multi-stroke pumping. Existing solutions also propose a method of pre-shaping the beam into an elliptical spot through a non-spherically symmetric light homogenizing tube, but it is difficult to ensure stable and reliable operation at high power. Summary of the Invention

[0005] In view of the above problems, this application is proposed. Embodiments of this application provide laser beam shaping applicable to off-axis, which can achieve uniform beam output of, for example, multi-stroke disk lasers.

[0006] According to an exemplary embodiment, a laser beam shaping device is provided, which is characterized by including: a collimation module for forming collimated light from the input pump beam; a shaping module for shaping the meridional direction beam and the sagittal direction beam of the collimated light; and a focusing module for focusing the meridional direction and sagittal direction beams after shaping to form a flat-top spot.

[0007] In some embodiments, the collimation module includes a collimation lens, and the numerical aperture of the lens of the collimation lens is greater 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 arranged along the direction of the light beam. Among them, the spherical mirror is used to adjust the beam sizes of the collimated light in the meridional direction and the sagittal direction, and the hybrid cylindrical mirror is used to adjust the size of the meridional-direction beam relative to the sagittal-direction beam, so as to form a flat-top light spot on the focal plane of the focusing module.

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

[0010] In some embodiments, the first cylindrical mirror has a focal power characteristic in the meridional direction, and the second cylindrical mirror has a focal power characteristic in the sagittal direction, so that a collimated beam in the meridional direction is formed after the light beam passes through the spherical mirror and the first cylindrical mirror, and a collimated beam in the sagittal direction is formed after passing through the spherical mirror and the second cylindrical mirror.

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

[0012] In some embodiments, the focusing module is a parabolic mirror.

[0013] In some embodiments, the materials of the collimating module, the shaping module, and the focusing module are composed of one or more of fused quartz, titanium silicate glass, and borosilicate glass.

[0014] In some embodiments, the flat-top light spot is a symmetric circular light spot.

[0015] According to an exemplary embodiment, a laser module is further provided, which is characterized by including: a pump source for outputting a pump beam; the aforementioned laser beam shaping device for converting the pump beam into a flat-top pump light spot; and a disk gain medium, which receives the energy of the pump light spot and generates laser light.

[0016] Based on some embodiments, the shaping device of the present application can obtain a uniform light spot on the focal plane and form a symmetric flat-top laser by separating the beam shaping in the meridional and sagittal directions and combining the beam focusing operation. The shaping device and method of the present application are widely applicable. For example, they can be applied to off-axis laser beam shaping and the pump source beam shaping of a multi-stroke disk laser head module. It can effectively correct the spot degradation introduced by off-axis, form a flat-top beam on the disk gain medium, thereby ensuring the stable and reliable operation of the laser system at high power.

[0017] The above and other features and advantages of the present invention will become apparent from the following description of exemplary embodiments in conjunction with the accompanying drawings. It should be understood that the exemplary embodiments do not necessarily achieve all of these advantages. Thus, the present invention may be embodied or implemented in a manner that realizes or optimizes one or a group of advantages as taught herein, without necessarily realizing other advantages as taught or suggested herein. Description of the Drawings

[0018] Figure 1 Schematic diagram of a pump light spot according to the prior art is shown;

[0019] Figure 2 Schematic diagram of the overall structure of a shaping device according to an embodiment of the present application is shown;

[0020] Figure 3 Schematic diagram of the specific structure of a shaping device according to an embodiment of the present application is shown;

[0021] Figures 4A - 4C Schematic diagram of the structure of a hybrid cylindrical lens according to an embodiment of the present application is shown;

[0022] Figure 5 Schematic diagram of the light spot at the disk gain medium after shaping the pump light spot by using the shaping device according to an embodiment of the present application is shown.

[0023] The corresponding component names represented by the reference numerals in the drawings are as follows:

[0024] 10 - pump source, 110 - collimating lens, 122 - spherical mirror, 124 - hybrid cylindrical lens, 130 - parabolic mirror, 20 - disk gain medium. Detailed Description of the Embodiments

[0025] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments of the present application. In the drawings, the same reference numerals generally represent the same components. It should be understood that the sizes and dimensions of the components shown in the drawings are not necessarily drawn to scale, and they may be different from those in the embodiments shown herein for implementation. In addition, some embodiments may combine any suitable combination of features from two or more drawings.

[0026] As described in the background art section, for a multi - stroke disk laser head module, it is usually necessary to off - axis introduce the pump source laser into the disk gain medium, which will lead to the deterioration of the light wave uniformity. Figure 1The schematic diagram of the pump spot in the prior art is shown. The left figure shows the pump laser spot after single - stroke degradation, and the right figure shows the spot after multi - stroke pumping. It can be seen that the degraded spot after a single stroke is elliptical, and the final output spot after multi - stroke is generally circular through the superposition effect. However, the energy distribution is uneven in the X and Y directions, the energy attenuation at the edge is different, the flat - top effect is poor, and the true - roundness of the spot is not good. This uneven high - power pump spot will cause surface irregularities due to thermal effects and the superposition of soft apertures. The spot excited by multi - stroke superposition will also deteriorate, and when the surface changes seriously, it may even cause the crystal to break.

[0027] To solve this technical problem, the embodiments of the present application provide a device and method for shaping a laser beam. Figure 1 The schematic diagram of the overall structure of a laser shaping device according to an embodiment of the present application is shown. As Figure 1 shown, the laser shaping device may include a collimation module 110, a shaping module 120, and a focusing module 130. Among them, the collimation module 110 can be used to receive the pump light output by the pump source 10 (for example, a semiconductor laser) and shape the input pump beam into a collimated light; the shaping module 120 is coaxially arranged with the collimation module 110 (that is, along the optical axis direction of the pump beam). It receives the collimated beam and shapes the meridional - direction beam and the sagittal - direction beam of the collimated light; the focusing module 130 can be arranged off - axis with respect to the shaping module 110 and the collimation module. It focuses the shaped beam (including the meridional - direction and sagittal - direction beams) and forms a flat - top spot. The energy of this flat - top pump spot can be received and absorbed by the laser gain medium 20 arranged at the focal plane to generate laser.

[0028] The technical solution of the embodiments of the present application can be applied to the shaping of the pump source beam of a multi - stroke disk - type laser head module. By separating the shaping of the meridional and sagittal beams and combining the characteristics of the focusing module, it can correct the spot degradation introduced by off - axis, realize obtaining a uniform spot at the focal plane, and thus ensure the stable and reliable operation of the laser system at high power.

[0029] The following will illustrate some specific embodiments of the present invention through the specific structure of the shaping device. However, it can be understood that this description only shows the preferred solutions of the present invention and does not limit the embodiments of the present invention.

[0030] Figure 3 The schematic diagram of the structure of a shaping device applicable to a disk - type laser system according to an embodiment of the present application is shown, and it also shows the single - stroke pump optical path. As described in detail below, Figure 3 the shown disk - type laser module generally includes a pump source, a shaping device, and a laser output module.

[0031] The pump source 10 is used to output pump light. For example, a pulsed semiconductor laser, a solid laser, etc. can be selected for pumping. The wavelength of the pump light generated by the pump source is within the absorption spectrum range of the laser gain medium 20, such as 700 - 1500 nm, preferably 800 - 1000 nm of laser. In one example, the beam emitted by the pump source 10 is a Gaussian beam with a circular distribution. It can be understood that this is only an example, and the beam is not limited to the Gaussian distribution. For example, it can also be an Airy distribution.

[0032] The shaping device includes a collimation module 110, a shaping module 120, and a focusing module 130. Among them, the collimation module 110 includes a collimation lens, which is used to collimate the input pump light into a parallel beam. In one example, the numerical aperture (NA) of the lens of the collimation lens 110 is greater than the numerical aperture of the input pump beam (i.e., the output spot of the pump source 10). In this way, the collimation lens can be installed relative to the pump source with a large margin and all the energy of the pump light can be optically coupled. In this sense, it can also be considered that the pump source 10 and the collimation lens together form the collimation module 110. As shown in the figure, in one example, the beam output from the collimation lens to the subsequent shaping module 120 is an expanded beam, which also satisfies the Gaussian distribution or is other optical distributions.

[0033] Combined Figure 1 and Figure 3 , the shaping module 120 of this embodiment includes two parts of structures arranged along the beam direction: a spherical mirror 122 and a hybrid cylindrical mirror 124. The collimated beam passes through the spherical mirror 122 and the hybrid cylindrical mirror 124 in sequence. Among them, the spherical mirror 122 can be used to adjust the beam sizes of the input collimated light in the meridional direction and the sagittal direction, and the hybrid cylindrical mirror 124 can be used to adjust the size of the meridional direction beam relative to the sagittal direction beam (it can also be said to adjust the sagittal direction beam relative to the meridional direction beam), so as to form a flat-top spot at the focal plane of the subsequent focusing module 130.

[0034] In one embodiment, the collimated light can be normally incident on the spherical mirror 122, so as to ensure that the adjustment of the beam sizes in the meridional direction and the sagittal direction is equivalent or basically the same. The spherical mirror 122 can be a positive lens or a 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 uses a positive lens (correspondingly, the lens 124 can use a negative cylindrical lens for collimation); when the shaping module 120 is used for beam contraction and shaping, the lens 122 uses a negative lens (correspondingly, the lens 124 can use a positive cylindrical lens for collimation).

[0035] Typically, as Figure 3As shown, the shaping module 120 is used for beam expansion and shaping. For example, the hybrid cylindrical lens 124 is located between the spherical mirror 122 and its focal point, and the size of the final output light spot can be adjusted by controlling the size of the light spot converging at the lens 124 by adjusting the position of the hybrid cylindrical lens 124 relative to the spherical mirror 122. In one example, the focal length of the spherical mirror 122 is 50 - 100 mm, and the distance between the hybrid cylindrical lens 124 and the spherical mirror 122 is 15 - 40 mm. This distance can be adjusted to first converge the light spot size to an appropriate size, and then the hybrid cylindrical lens 124 collimates and expands the light beam.

[0036] In this article, the meaning of "hybrid cylindrical lens" is that the cylindrical lens includes multiple cylinders or is composed of multiple cylindrical lenses. These multiple cylinders or cylindrical lenses can be respectively used for shaping the meridional direction and sagittal direction of the light beam, so as to adjust the size of the meridional direction light beam relative to the sagittal direction light beam as a whole, and at the same time adjust the phase of the light beam for uniform light processing. In one example, the hybrid cylindrical lens 124 may include a first cylindrical lens and a second cylindrical lens arranged in sequence, and the light beam is incident on the first cylindrical lens and the second cylindrical lens in sequence. In this way, the hybrid cylindrical lens 124 can achieve separate shaping of the light beam in the meridional direction and sagittal direction. For example, the first cylindrical lens has a focal power characteristic in the meridional direction (YZ direction), that is, it collimates at least the meridional direction light beam, and may not have a shaping effect on the sagittal direction light beam. The second cylindrical lens has a focal power characteristic in the sagittal direction (XZ direction), that is, it collimates the sagittal direction light beam, and may not have a shaping effect on the meridional direction light beam, and the focal power characteristics of the two may be different. In this way, the light beam forms a collimated light beam in the meridional direction after passing through the spherical mirror 122 and the first cylindrical lens, and the light beam forms a collimated light beam in the sagittal direction after passing through the spherical mirror 122 and the second cylindrical lens. Alternatively, the light beam forms a collimated light beam in the sagittal direction after passing through the spherical mirror 122 and the first cylindrical lens, and the light beam forms a collimated light beam in the meridional direction after passing through the spherical mirror 122 and the second cylindrical lens. Here, "collimation" is intended to indicate that the divergence angle of the light beam decreases after shaping, not that an absolutely parallel light beam is formed.

[0037] Figures 4A - 4C The structural schematic diagram of the hybrid cylindrical lens 124 according to an embodiment of the present application is shown. As Figure 4A shown, the hybrid cylindrical lens 124 includes two cylinders, front and back, along the optical axis (Z axis) of the light beam. Or rather, it includes two cylindrical lenses, front and back, which are respectively used for shaping the meridional direction light beam and the sagittal direction light beam. Preferably, as shown in the figure, the two cylindrical lenses are integrally processed and formed within the same lens, so as to ensure that component crosstalk is not introduced due to alignment and adjustment, and improve the shaping effect of the output light spot. However, the present application is not limited thereto. In some examples, two separate lenses may also be used to form the cylindrical shaping part.

[0038] Figures 4B - 4C shows Figure 4A the front side view and the oblique side view of the hybrid cylindrical lens. As shown in the figure, the hybrid cylindrical lens 124 can be regarded as composed of the cylindrical lens 124-1 and the cylindrical lens 124-2. The cross-section (XY plane) of the two cylindrical lenses is circular. Among them, the cylindrical lens 124-1 has the optical power characteristic in the YZ direction and can collimate the meridional direction beam, and the cylindrical lens 124-2 has the optical power characteristic in the XZ direction and can collimate the sagittal direction beam. The beam first passes through the cylindrical lens 124-1 to form a collimated beam in the meridional direction, and then passes through the cylindrical lens 124-2 to form a collimated beam in the sagittal direction. In the figure, the cylindrical lens 124-1 and the cylindrical lens 124-2 are shown as negative lenses (concave surfaces). Combined with Figure 3 , it can form an expanding and shaping module with the spherical mirror 122. It can be understood that when the spherical mirror 122 is selected as a negative lens, the cylindrical lens 124-1 and the cylindrical lens 124-2 can be positive cylindrical lenses (convex surfaces) to achieve beam shrinking and shaping. It can also be understood that the positions of the cylindrical lens 124-2 and the cylindrical lens 124-1 can be interchanged, that is, the beam first passes through the cylindrical lens 124-2 and then passes through the cylindrical lens 124-1 for beam shaping.

[0039] In a preferred embodiment, the materials of the collimating lens 110, the spherical mirror 122 and the hybrid cylindrical lens 124 can be composed of one or more of fused silica, titanium silicate glass, borosilicate glass, including but not limited to optical glasses such as ULE and BK7, which have a low coefficient of thermal expansion and can withstand high-power pump light.

[0040] Return Figure 3, a focusing module 130 is disposed off-axis on the output optical path after the beam is shaped by the spherical mirror and the hybrid cylindrical mirror. The focusing module 130 can be a parabolic mirror for focusing the beam and guiding it to the disk-shaped gain medium 20 coaxial with the parabolic mirror. Similar to the lenses 110, 122, and 124, the parabolic mirror 130 can also be made of materials such as fused quartz, titanium silicate glass, and borosilicate glass. As shown in the figure, the focused beam will be obliquely incident on the laser gain medium 20. The laser gain medium 20 is used to absorb the pump light and provide gain to generate stimulated radiation light. For example, it can use laser crystal materials, 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 can 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 axial heat dissipation ability of the thin crystal is better, which is beneficial to stable operation. In one example, when the input pump beam is loaded onto the disk-shaped gain medium 20, a large amount of waste heat will be generated. To eliminate its adverse effects on optical devices, heat dissipation treatment is required. For this purpose, a heat sink and other heat dissipation devices 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. Regarding the heat sink and the setting method with the disk crystal, reference can be made to the Chinese patent application CN 202520164712.0 of the present inventor and applicant, and the entire content of this patent document is incorporated into this application by reference herein.

[0041] As described above, since the pump beam has been separated and shaped in the meridional direction and the sagittal direction, the embodiment of the present application can achieve a symmetric flat-top pump spot at the disk crystal 20 in a single stroke. Figure 5 The schematic diagram of the single-stroke pump spot obtained after shaping the pump light by the shaping device of the embodiment of the present application is shown. As shown in the figure, the beam passes through the lenses 122, 124, and the parabolic mirror 130, and a flat-top uniform spot with a larger spot size can be obtained. The spot is a symmetric circular spot, and the energy at each part of the spot is relatively uniform. Due to the existence of the damage threshold of the disk crystal, a larger pump uniform spot size is beneficial to high-power laser output and ensures the stable operation of the system at high power.

[0042] Although Figure 3Only a single - stroke optical path is shown. It can be understood that by setting total - reflection mirrors (not shown), multi - stroke pumping can be achieved. For example, the laser gain medium 20 receives part of the energy of the pump light and reflects the unabsorbed part at the same time. Total - reflection mirrors on the reflection path (for example, one can be set above and below the laser gain medium 20 respectively) can conduct the reflected pump light to the laser gain medium 20 again and absorb the remaining energy of the pump light. After multiple strokes, 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 sufficient energy extraction is output through the parabolic mirror 130, that is, the parabolic mirror 130 also constitutes a part of the laser output module at the same time.

[0043] An exemplary embodiment of the present invention further provides a disk laser or an optical system including the above - mentioned laser beam shaping device. As described above, the shaping device can be used to convert the pump beam into a flat - topped pump light spot. In addition to this shaping device, it can also include components such as a pump source, a laser output module, etc. Among them, the laser output module can include a disk - type gain medium, an output parabolic mirror, etc. (which can also be used as the focusing lens in the shaping device at the same time). This laser amplification device can be applied to fields such as circuit manufacturing, radar detection, and optical fiber communication.

[0044] The above refers to Figures 2 - 5 The exemplary structures and compositions of the laser beam shaping device of the present application and the disk - type laser module including it are described. By, for example, the shaping module, beam shaping in the two directions of the meridional and sagittal directions can be separated, and combined with the beam focusing operation, the spot degradation caused by off - axis can be corrected, a uniform spot can be obtained on the focal plane, and a symmetric flat - topped laser can be formed, which helps the laser optical system to operate stably and reliably at high power.

[0045] It should be understood that although terms such as "first" or "second" may be used in this article to describe different components or features, these components or features are not limited to these terms. Using the above terms, only one part is distinguished from another part, rather than emphasizing the order, positional relationship, etc. For example, without departing from the scope of the present disclosure, the first component can be called the second component; and the second component can also be called the first component. That is to say, modifiers without quantifiers such as "first" and "second" are interchangeable.

[0046] In this article, words such as "including", "comprising", "having", etc. are open - ended words, meaning "including but not limited to", and can be used interchangeably with each other. The word "or" and "and" used here refer to the word "and / or", and can be used interchangeably with each other unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to", and can be used interchangeably with each other.

[0047] The embodiments of the present application have been described above. The above description is exemplary and not exhaustive, and is also not limited to the disclosed embodiments. Many combinations, modifications, and changes will be obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A laser beam shaping device, characterized in that: include: A collimation module, which is used to form an input pump beam into a collimated light; A shaping module, used for shaping the meridional beam and the sagittal beam of the collimated light; as well as A focusing module is used to focus the shaped light beams in the meridian and sagittal directions to form a flat-top spot.

2. The laser beam shaping device according to claim 1, characterized in that: The collimating module comprises a collimating lens, and the numerical aperture of the lens of the collimating lens is greater than the numerical aperture of the input pump light beam.

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

4. The laser beam shaping device according to claim 3, characterized in that: The hybrid cylindrical mirror comprises a first cylindrical mirror and a second cylindrical mirror, wherein the first cylindrical mirror and the second cylindrical mirror are located in the same lens.

5. The laser beam shaping device according to claim 4, characterized in that: The first cylindrical mirror has an optical focal length characteristic in the meridional direction, and the second cylindrical mirror has an optical focal length characteristic in the sagittal direction, so that the light beam forms a collimated light beam in the meridional direction after passing through the spherical mirror and the first cylindrical mirror, and forms a collimated light beam in the sagittal direction after passing through the spherical mirror and the second cylindrical mirror.

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

7. The laser beam shaping device according to claim 1 or 2, characterized in that: The focusing module is a parabolic reflector.

8. The laser beam shaping device according to claim 1 or 2, characterized in that: The collimating module, the shaping module and the focusing module are made of one or more materials selected from the group consisting of fused quartz, titania silicate glass and borosilicate glass.

9. The laser beam shaping device according to 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: A pump source, used for outputting a pump beam; The laser beam shaping device according to any one of claims 1 to 9, used for converting the pump beam into a flat-top pump spot; as well as The disk gain medium receives the energy of the pump light spot and generates laser.

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