A pump module, laser and laser amplifier with controllable thermal focal length

Abstract

The present invention relates to the field of laser technology, and specifically provides a pump module with controllable thermal focus, a disk laser, and a laser amplifier. The pump module with controllable thermal focus includes: a multi-pass coupling cavity for pumping the pump light multiple times in the multi-pass coupling cavity, including a thin sheet laser crystal; a light source module including a plurality of matrix-arranged light sources, wherein the plurality of matrix-arranged light sources respectively form a plurality of irradiation areas on the laser crystal, and the power of the plurality of matrix-arranged light sources is adjusted to make the optical path difference of each irradiation area on the laser crystal consistent; and a collimation module for collimating the outgoing light beam of the light source module. The present invention customizes a light source spot with a specific light intensity distribution according to the surface shape of the disk crystal, aiming to achieve uniform temperature distribution inside the disk. By designing the light intensity distribution of the incident light according to the surface shape of the disk crystal, it can be ensured that the optical path difference of each point of the disk crystal remains consistent during the increase of the pump power.

Description

Technical Field

[0001] The present invention relates to the technical field of laser equipment, and in particular to a pump module, a laser and a laser amplifier with controllable thermal focal length. Background Art

[0002] Since the advent of the first laser in 1960, achieving high-power, high-conversion efficiency, and high-beam-quality laser output has been the primary goal of laser development. However, the thermal lensing effect in solid-state lasers severely limits further improvements in output laser power and quality, and can even lead to breakage of the gain medium. Furthermore, the thermal lensing effect of the crystal can significantly affect the population distribution at the laser energy level, causing a sharp drop in the laser's conversion efficiency. Therefore, to further improve the output power, conversion efficiency, and output beam quality of semiconductor-pumped solid-state lasers, it is necessary to minimize the thermal lensing effect of the laser crystal during laser system operation.

[0003] The gain medium of the disk laser is in the shape of a thin disk, usually 100 to 400 µm thick and 10 to 20 mm in diameter. A material with excellent thermal conductivity, such as diamond or copper-tungsten alloy, is connected to the back surface of the disk crystal as a heat sink. The waste heat in the disk crystal is efficiently extracted by shock water cooling, which can suppress the thermal lens effect in solid-state lasers. Therefore, disk lasers have become one of the best choices for achieving high power, high conversion efficiency and high beam quality in lasers, and are widely used in basic scientific research, industrial production, biomedicine, national defense and military fields. Nevertheless, for high-power disk lasers, although the thermal lens effect has been significantly suppressed compared to traditional solid-state lasers, the residual thermal lens effect still has a certain impact on the laser output, becoming a key factor restricting its development.

[0004] Currently, methods for compensating for the thermal lensing effect of Yb:YAG disk crystals primarily include improving pump uniformity, reducing disk crystal thickness, and using thicker diamond heat sinks and 969 nm semiconductor lasers as pump sources. However, due to the complexity of multi-pass pumping of disk lasers and the disk crystal's inefficient absorption of pump light, commercial pump modules still face the challenge of thermal lensing in high-power applications, limiting further improvement and development of disk laser performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a pump module, laser, and laser amplifier with controllable thermal focal length, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows:

[0006] According to a specific embodiment disclosed in the present invention, a first aspect of the present invention discloses a pump module with controllable thermal focal length, comprising: a multi-pass coupled cavity for causing pump light to be pumped multiple times within the multi-pass coupled cavity, comprising a thin sheet-like laser crystal;

[0007] A light source module, the light source module comprising a plurality of light sources arranged in a matrix, the plurality of light sources arranged in the matrix forming a plurality of irradiation areas on the laser crystal, and adjusting the power of the plurality of light sources arranged in the matrix to make the optical path difference of each irradiation area on the laser crystal consistent;

[0008] The collimating module collimates the outgoing light beam of the light source module.

[0009] Preferably, the light source module comprises: a semiconductor laser and a beam shaping mirror, and the outgoing light beam of the semiconductor laser forms a plurality of irradiation areas on the laser crystal after passing through the beam shaping mirror, and the light intensity value of each irradiation area is different.

[0010] Preferably, the beam shaping mirror comprises: a microlens array, a fly-eye lens or an M-type beam shaping mirror.

[0011] Preferably, the light source module is a laser diode array, and the powers of the laser diodes in the laser diode array are different, so that the outgoing light beam forms multiple irradiation areas on the laser crystal, and the light intensity value of each irradiation area is different.

[0012] Preferably, the multi-pass coupled cavity comprises: a 4f optical system and a laser crystal module, wherein the laser crystal module is placed in the optical path of the 4f optical system, so that the light beam emitted by the light source module is pumped multiple times in the multi-pass coupled cavity.

[0013] Preferably, the pump module with controllable thermal focal length further includes: a measurement module connected to the multi-pass coupling cavity, for obtaining the temperature gradient distribution of the laser crystal and the optical path difference of the irradiated area during pumping; taking the temperature of the area with the smallest optical path difference as the reference temperature, determining the incident light power corresponding to other areas on the laser crystal, making the temperature of the other areas close to the reference temperature, and obtaining the light intensity value of each area on the laser crystal at this time.

[0014] Preferably, the thermal focal length controllable pump module also includes: a light intensity adjustment module, which is connected to the light source module, and adjusts the outgoing light beam of the light source module according to the light intensity value of each area on the laser crystal, so that the energy distribution of the light spot of the outgoing light beam corresponds to the light intensity value of each area on the laser crystal.

[0015] Preferably, the change in the focal length of the thermal lens of the laser crystal is less than 0.005 m -1 .

[0016] According to a specific embodiment disclosed in the present invention, a second aspect of the present invention discloses a disk laser, comprising the above-mentioned pump module with controllable thermal focal length.

[0017] According to a specific embodiment disclosed in the present invention, a third aspect of the present invention discloses a disk laser amplifier, comprising the above-mentioned pump module with controllable thermal focal length.

[0018] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects:

[0019] This invention customizes the pump light source spot with a specific light intensity distribution according to the surface shape of the disk crystal, aiming to achieve uniform temperature distribution inside the disk. By designing the incident light intensity distribution according to the surface shape of the disk crystal, it can ensure that the optical path difference at each point of the disk crystal remains consistent during the process of increasing the pump power, so that the change of the thermal lens focal length is less than 0.005m. -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are incorporated into and constitute a part of the specification, illustrating embodiments consistent with the present disclosure and, together with the specification, explaining the principles of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort. In the drawings:

[0021] Figure 1 A schematic structural diagram of a pump module with controllable thermal focal length provided by an embodiment of the present invention;

[0022] Figure 2 A schematic structural diagram of a pump module provided in another embodiment of the present invention;

[0023] Figure 3 A schematic diagram of light intensity distribution provided by an embodiment of the present invention.

[0024] Reference numerals:

[0025] 10. Light source module, 11. Semiconductor laser, 12. Beam shaping lens,

[0026] 31. First parabolic mirror, 32. Second parabolic mirror,

[0027] 20. Multi-pass coupled cavity, 41. First 45° reflector group, 42. Second 45° reflector group, 5. Disc crystal, 6. Disc heat sink, 7. Fixture, 8. Water cooling channel, 30. Collimation module. DETAILED DESCRIPTION

[0028] To further clarify the objectives, technical solutions, and advantages of the present invention, a pump module, laser, and laser amplifier with controllable thermal focus disclosed herein will be described in further detail below with reference to the accompanying drawings. It should be understood that the embodiments described herein represent only a portion of the embodiments disclosed herein, and not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments disclosed herein without inventive effort are intended to fall within the scope of protection disclosed herein.

[0029] The terms used in the examples of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms "a," "the," and "the" used in the examples of this application and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0030] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0031] It should be understood that although the terms first, second, third, etc. may be used to describe in the embodiments of the present application, these should not be limited to these terms. These terms are only used to distinguish. For example, without departing from the scope of the embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0032] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprising a" does not exclude the presence of other identical elements in the product or device comprising the element.

[0033] In the method of correcting the thermal lens effect of disk lasers, reducing the thickness of the disk crystal helps to weaken the temperature and stress gradient inside the disk crystal, thereby achieving compensation. However, due to the need to take into account both the complexity of the disk laser multi-pass pumping system and the absorption efficiency of the disk crystal to the pump light, the thickness of the doped disk crystal in the commercial disk crystal module cannot be less than 100μm. After using a flat-top / super-Gaussian pump source with a wavelength of 969 nm, the aspheric term of the thermal lens effect of the existing commercial disk crystal equipped with a diamond heat sink has almost been reduced to the limit. However, as the pump power density increases to 5kW / cm2 When the optical power of the disk crystal is changed, it will still produce a certain degree of optical focal length change, which cannot meet the requirements of the near-collimated multi-pass amplifier in the disk laser for minimal optical focal length change. In order to better suppress the thermal lens effect, the present invention proposes a pump module with controllable thermal focal length. Figure 1-3 Alternative embodiments of the present invention are described in detail.

[0034] Example 1:

[0035] like Figure 1 As shown, according to a specific embodiment of the present invention, the present invention provides a pump module with controllable thermal focal length, comprising:

[0036] A multi-pass coupling cavity 20, for pumping the pump light multiple times in the multi-pass coupling cavity, comprising a thin sheet of laser crystal;

[0037] A light source module 10, comprising a plurality of light sources arranged in a matrix, wherein the plurality of light sources arranged in the matrix form a plurality of irradiation areas on the laser crystal, and wherein the power of the plurality of light sources arranged in the matrix is adjusted so that the optical path difference of each irradiation area on the laser crystal is consistent;

[0038] The collimating module 30 collimates the outgoing light beam of the light source module.

[0039] Compared with the existing technology that optimizes the distribution of the outgoing beam spot to form a uniform spot on the gain medium, the present invention changes the light intensity of the outgoing beam spot to form an uneven spot on the gain medium, thereby keeping the optical path difference of each area on the disk crystal consistent and reducing the thermal lens effect.

[0040] As an optional embodiment, the thin-sheet laser crystal may be a disk crystal used for a disk laser, with a thickness of 0.1-0.5 mm.

[0041] As an optional embodiment, the light source module 10 can be a laser diode array. By adjusting the luminous intensity of each laser diode in the laser diode array, the light spots with uneven light intensity distribution are formed after coupling. Multiple irradiation areas are formed on the disk crystal, and the light intensity value of each irradiation area is different.

[0042] As an optional embodiment, the light source module 10 includes a semiconductor laser 11 and a beam shaping lens 12. The beam shaping lens 12 shapes the laser light emitted by the semiconductor laser 11. After passing through the beam shaping lens, the output beam of the semiconductor laser forms multiple irradiation areas on the laser crystal, each irradiation area having a different light intensity.

[0043] Specifically, the beam shaping mirror may be a microlens array, a fly-eye lens, or an M-type beam shaping mirror capable of adjusting the light intensity distribution of the outgoing light beam.

[0044] As an optional embodiment, the collimating module 30 is placed on the outgoing light path of the light source module 10 to collimate the outgoing light beam adjusted by the light source module 10 so that the collimated light beam enters the multi-pass coupling cavity 20 .

[0045] As an optional embodiment, the multi-pass coupling cavity 20 includes: a 4f optical system and a laser crystal module, wherein the laser crystal module is placed in the optical path of the 4f optical system so that the light beam emitted by the light source module is pumped multiple times in the multi-pass coupling cavity.

[0046] Specifically, such as Figure 2 or Figure 1 As shown, the light beam emitted by the light source module passes through the first parabolic mirror 31 for the first time and is focused on the disk crystal 5. A portion of the light beam is absorbed the first time, and the remaining unabsorbed light beam is reflected a second time by the second parabolic mirror 32 and incident on the first 45° reflector assembly 42 as parallel light. After reflecting from the first 45° reflector assembly 42, the light beam is reflected again as parallel light by the second parabolic mirror 32 and focused a second time on the disk crystal 5, completing the secondary pumping. After passing through the first parabolic mirror 31 again, the light beam is reflected back to the first parabolic mirror 31 as parallel light by the second 45° reflector assembly 41, completing the reciprocating pumping cycle.

[0047] Furthermore, in order to achieve efficient heat exchange, a disc heat sink 6 is fixed to the back of the disc crystal 5 by a clamp 7. The disc heat sink 6 is made of a material with good thermal conductivity such as diamond or copper tungsten, and a water cooling channel 8 is set inside it.

[0048] As an optional implementation, the pump module with controllable thermal focal length further includes: a measurement module and a light intensity adjustment module.

[0049] Furthermore, a measurement module is connected to the multi-pass coupling cavity and is used to obtain the temperature gradient distribution of the laser crystal and the optical path difference of the irradiated area during pumping; the temperature of the area with the smallest optical path difference is used as the reference temperature to determine the incident light power corresponding to other areas on the laser crystal, so that the temperature of the other areas is close to the reference temperature, and the light intensity value of each area on the laser crystal at this time is obtained.

[0050] The light intensity adjustment module is connected to the light source module and adjusts the outgoing light beam of the light source module according to the light intensity values of each area on the laser crystal, so that the energy distribution of the light spot of the outgoing light beam corresponds to the light intensity values of each area on the laser crystal.

[0051] The working principle of a pump module with controllable thermal focal length provided by the present invention is described below.

[0052] Once the surface shape of the disk crystal is known, the temperature distribution on the disk crystal is measured using a thermal imager and interferometer or a wavefront sensor with reference light. Software is then used to determine the optical path difference at each measurement point on the disk crystal. Thermal simulation is performed using COMSOL Multiphysics finite element analysis software to obtain a pump light intensity distribution that matches the focal length of the thermal lens. Based on this intensity distribution, the individual point light source spots in the light source module 10 are adjusted to reflect the simulated intensity distribution.

[0053] Using a laser diode array as the light source Figure 3 Take the light intensity distribution diagram corresponding to the spherical disk crystal shown as an example.

[0054] In this embodiment, when measuring the optical path difference, it is assumed that the laser array produces a uniform light spot. After a period of irradiation, a thermal lens effect will occur on the disc crystal. When the output light of the light source module 10 increases to a pump power that meets the pump power density, the measurement at a certain moment is performed. t Optical path difference The moment was measured by a thermal imager. t The temperature gradient distribution value of the disk crystal at that moment is obtained by interferometer, and the optical path difference of each measurement point on the disk crystal is deduced. In this example, 10 kW / cm 2 The pump power density.

[0055] According to the difference in optical path difference, the measurement area on the disk crystal can be roughly divided into four areas. For example, point D is located in the center of the 4×4 area. The optical path difference of each point in the center area is almost the same, which is expressed as , the corresponding light intensity value is expressed as Point C is located in the outer circle of the central area, which is recorded as the second area. The optical path difference of each point in the second area is almost the same, which is expressed as , the light intensity value is expressed as Similarly, it can be expanded outward to the third area and the outermost area, and the optical path difference of each point in it is expressed as ; The light intensity values are expressed as and Moreover, there is a relationship between the optical path differences of various regions: .

[0056] In order to make the optical path difference of each point on the disk crystal consistent and minimize the thermal lens effect, the optical path difference The temperature corresponding to the minimum point is the reference for adjustment. By reducing the heat generated in the area with the largest optical path difference, the optical path difference is reduced, that is, the incident light intensity in the area with the largest optical path difference is lowered. At this time, the adjustment amount of the incident light intensity is The maximum value of .

[0057] Combined with software analysis, we need to get Figure 3 The light intensity distribution diagram of a laser diode array, which can achieve consistent optical path differences at all points on a disk crystal, is shown as an M-shaped pattern. Based on the adjustment requirements, a 10x10 laser diode array was selected and the output parameters of each laser diode within the array were adjusted. The grayscale represents the intensity, with increasing intensity followed by decreasing intensity from the inside out.

[0058] In this embodiment, if Figure 1 As shown, each laser diode in the laser diode array outputs in the form of fiber coupling. At this time, the collimating module 30 used for collimation can be a microlens array, which couples and collimates the point light sources with different powers adjusted by the laser diode array.

[0059] It has been verified that by changing the energy distribution of the light source spot, the focal length of the thermal lens of the disk crystal can be changed to less than 0.005m. -1 .

[0060] Alternatively, a semiconductor laser 11 is used as the pump light source, and the beam shaping lens 12 is a microlens array. By adjusting the parameters of each microlens in the microlens array, the light spot of the light beam emitted by the microlens can be made to have the light intensity distribution of the simulation results. In this embodiment, each light beam emitted by the microlens can be considered as a point light source. By changing the position or shape of each microlens, the output light beam can have different power values, thereby forming multiple irradiation areas with different light intensities on the laser crystal, and ensuring that the optical path difference of each irradiation area on the laser crystal is consistent.

[0061] Example 2:

[0062] The present invention also provides device embodiments that are consistent with the above embodiments. The interpretations based on the same name meanings are the same as those of the above embodiments, and have the same technical effects as the above embodiments, which will not be repeated here.

[0063] The present invention discloses a disk laser, comprising a pump module with controllable thermal focal length.

[0064] Example 3:

[0065] The present invention also provides device embodiments that are consistent with the above embodiments. The interpretations based on the same name meanings are the same as those of the above embodiments, and have the same technical effects as the above embodiments, which will not be repeated here.

[0066] The present invention discloses a disk laser amplifier, comprising a pump module with controllable thermal focal length.

[0067] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. References to the common and similar parts between the various embodiments will be sufficient. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, their descriptions are relatively simple; for relevant details, refer to the descriptions of the methods.

[0068] The above embodiments are only used to illustrate the technical solutions disclosed in the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments disclosed in the present invention.

Claims

1. A pump module with controllable thermal focal length, characterized in that: include: A multi-pass coupling cavity, used to allow pump light to be pumped multiple times in the multi-pass coupling cavity, including a thin-sheet laser crystal; A light source module is capable of forming multiple irradiation areas on the laser crystal, and the power of the light source module is adjusted to make the optical path difference of each irradiation area on the laser crystal consistent; A collimating module, for collimating the outgoing light beam of the light source module; The light source module includes: a semiconductor laser and a beam shaping mirror. The outgoing light beam of the semiconductor laser forms a plurality of irradiation areas on the laser crystal after passing through the beam shaping mirror. The light intensity value of each irradiation area is different. The beam shaping mirror is an M-type beam shaping mirror; or The light source module is a laser diode array. The power of each laser diode in the laser diode array is different, so that the outgoing light beam forms multiple irradiation areas on the laser crystal, and the light intensity value of each irradiation area is different.

2. The thermal focus controllable pump module according to claim 1, characterized in that: The multi-pass coupling cavity further includes: a 4f optical system, and the laser crystal is placed in the optical path of the 4f optical system, so that the light beam emitted by the light source module is pumped multiple times in the multi-pass coupling cavity.

3. The pump module with controllable thermal focus according to claim 1, wherein: Also includes: A measurement module is connected to the multi-pass coupling cavity and is used to obtain the temperature gradient distribution of the laser crystal and the optical path difference of the irradiated area during pumping; the temperature of the area with the smallest optical path difference is used as the reference temperature, and the incident light power corresponding to other areas on the laser crystal is determined so that the temperature of the other areas is close to the reference temperature, thereby obtaining the light intensity value of each area on the laser crystal at this time.

4. The thermal focus controllable pump module according to claim 3, characterized in that: When the light source module is a laser diode array, the thermal focus controllable pump module further includes: a light intensity adjustment module, which is connected to the light source module and adjusts the outgoing light beam of the light source module according to the light intensity values of each area on the laser crystal, so that the energy distribution of the light spot of the outgoing light beam corresponds to the light intensity values of each area on the laser crystal.

5. The thermal focus controllable pump module according to claim 4, characterized in that: The change in focal length of the thermal lens of the laser crystal is less than 0.005m -1 .

6. A disk laser amplifier, characterized in that: The invention comprises the pump module with controllable thermal focal length as described in any one of claims 1 to 5.

7. A disk laser, characterized in that: The invention comprises the pump module with controllable thermal focal length as described in any one of claims 1 to 5.

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