Pumping module with controllable thermal focal length, laser and laser amplifier

Abstract

The invention relates to the technical field of laser, and particularly provides a pumping module with a controllable thermal focal length, a disc laser and a laser amplifier, and the pumping module with the controllable thermal focal length comprises a multi-pass coupling cavity which is used for enabling pumping light to be pumped for multiple times in the multi-pass coupling cavity and comprises a lamellar laser crystal; the light source module comprises a plurality of light sources arranged in a matrix, the plurality of light sources arranged in the matrix form a plurality of irradiation areas on the laser crystal respectively, and the power of the plurality of light sources arranged in the matrix is adjusted, so that the optical path differences of the irradiation areas on the laser crystal are consistent; and the collimation module is used for collimating the emergent light beam of the light source module. The light source light spots with specific light intensity distribution are customized according to the surface type of the disc crystal, and the purpose is to achieve uniform distribution of the temperature in the disc. Through the light intensity distribution of the incident light designed for the surface type of the disc crystal, the optical path difference of each point of the disc crystal can be ensured to be consistent in the process of increasing the pumping 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 always been the main goal of laser development. However, the thermal lens effect in solid-state lasers severely limits the further improvement of their output laser power and quality, and even worse, it can cause the gain medium to break. At the same time, the thermal lens effect of the crystal will greatly affect the distribution of the number of particles at the laser energy level, causing the conversion efficiency of the laser to drop sharply. Therefore, in order to further improve the output power, conversion efficiency and output beam quality of semiconductor-pumped solid-state lasers, it is necessary to suppress the thermal lens effect of the laser crystal as much as possible during the operation of the laser system.

[0003] The gain medium of the disk laser is a thin disk with a thickness of usually 100 to 400 µm and a diameter of 10 to 20 mm. It uses materials with excellent thermal conductivity such as diamond or copper-tungsten alloy to connect to the back surface of the disk crystal as a heat sink. The waste heat in the disk crystal is efficiently exported by impact 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] At present, the main methods for compensating the thermal lens effect of Yb:YAG disk crystals are: improving pump uniformity, reducing the thickness of disk crystals, using thicker diamond heat sinks and semiconductor lasers with a wavelength of 969 nm as pump sources. However, given the complexity of multi-pass pumping of disk lasers and the absorption efficiency of disk crystals for pump light, commercial pump modules still face the challenge of thermal lens effects in high-power applications, limiting the 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, a laser and a 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: According to the specific embodiments disclosed in the present invention, the present invention discloses, in a first aspect, a pump module with controllable thermal focal length, comprising: a multi-pass coupling cavity for causing pump light to be pumped multiple times in the multi-pass coupling cavity, comprising a thin sheet-like laser crystal; A light source module, wherein the light source module comprises a plurality of light sources arranged in a matrix, wherein the plurality of light sources arranged in a matrix respectively form a plurality of irradiation areas on the laser crystal, and the power of the plurality of light sources arranged in a matrix is ​​adjusted to make the optical path difference of each irradiation area on the laser crystal consistent; The collimation module is used to collimate the outgoing light beam of the light source module.

[0006] 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.

[0007] Preferably, the beam shaping mirror comprises: a microlens array, a fly-eye lens or an M-type beam shaping mirror.

[0008] 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 a plurality of irradiation areas on the laser crystal, and the light intensity value of each irradiation area is different.

[0009] Preferably, the multi-pass coupling 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 coupling cavity.

[0010] Preferably, the pump module with controllable thermal focal length also 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.

[0011] 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.

[0012] Preferably, the change in the focal length of the thermal lens of the laser crystal is less than 0.005 m -1 .

[0013] 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.

[0014] 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 thermal focal length controllable pump module.

[0015] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects: The present 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. Through the light intensity distribution of the incident light designed for the surface shape of the disk crystal, it can ensure that the optical path difference of each point of the disk crystal remains consistent during the increase of the pump power, so that the change of the focal length of the thermal lens is less than 0.005m. -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the disclosure of the present invention, and together with the specification, are used to explain the principles disclosed in the present invention. Obviously, the drawings described below are only some embodiments disclosed in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings: Figure 1 A schematic structural diagram of a pump module with controllable thermal focal length provided by an embodiment of the present invention; Figure 2 A schematic structural diagram of a pump module provided in another embodiment of the present invention; Figure 3 A schematic diagram of light intensity distribution provided by an embodiment of the present invention.

[0017] Reference numerals: 10. Light source module, 11. Semiconductor laser, 12. Beam shaping lens, 31. The first parabolic mirror, 32. The second parabolic mirror, 20. Multi-pass coupling cavity, 41. First 45° reflecting mirror group, 42. Second 45° reflecting mirror group, 5. Disc crystal, 6. Disc heat sink, 7. Fixture, 8. Water cooling channel, 30. Collimation module. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages disclosed in the present invention clearer, a pump module, laser and laser amplifier with controllable thermal focus disclosed in the present invention will be further described in detail in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments disclosed in the present invention, not all of the embodiments. Based on the embodiments disclosed in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection disclosed in the present invention.

[0019] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0020] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0021] 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.

[0022] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or device. In the absence of more restrictions, the elements defined by the sentence "comprises a" do not exclude the presence of other identical elements in the product or device including the elements.

[0023] In the correction method of 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 aspherical 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-collimation multi-pass amplifier in the disk laser for extremely small 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.

[0024] Embodiment 1: 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:

[0025] A multi-pass coupling cavity 20, used to allow pump light to be pumped multiple times in the multi-pass coupling cavity, including a thin sheet of laser crystal; A light source module 10, wherein the light source module comprises a plurality of light sources arranged in a matrix, wherein the plurality of light sources arranged in a matrix respectively form a plurality of irradiation areas on the laser crystal, and the power of the plurality of light sources arranged in a matrix is ​​adjusted so that the optical path difference of each irradiation area on the laser crystal is consistent; The collimation module 30 collimates the outgoing light beam of the light source module.

[0026] Compared with the prior art which optimizes the distribution of the outgoing light beam spot to form a uniform light spot on the gain medium, the present invention changes the light intensity of the outgoing light beam spot to form an uneven light 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.

[0027] As an optional implementation, the thin sheet-shaped laser crystal may be a disk crystal used for a disk laser, with a thickness of 0.1-0.5 mm.

[0028] As an optional embodiment, the light source module 10 can be a laser diode array, and the light intensity of each laser diode in the laser diode array is adjusted to form a light spot with uneven light intensity distribution after coupling. Multiple irradiation areas are formed on the disc crystal, and the light intensity value of each irradiation area is different.

[0029] As an optional embodiment, the light source module 10 includes: a semiconductor laser 11 and a beam shaping mirror 12, and the beam shaping mirror 12 is used to shape the laser light emitted by the semiconductor laser 11. After the output light beam of the semiconductor laser passes through the beam shaping mirror, a plurality of irradiation areas are formed on the laser crystal, and the light intensity value of each irradiation area is different.

[0030] 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.

[0031] As an optional implementation, the collimation module 30 is placed on the outgoing light path of the light source module 10 , and is used 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 .

[0032] As an optional implementation, 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.

[0033] Specifically, Figure 2 or Figure 1 As shown, after the light beam emitted by the light source module passes through the first parabolic mirror 31 for the first time, it is focused on the disk crystal 5 for the first time, a part of the light beam is absorbed for the first time, and the remaining unabsorbed light beam is reflected to the second parabolic mirror 32 for the second time, and is incident on the first 45° reflector group 42 as parallel light. After being reflected on the first 45° reflector group 42, it is reflected to the second parabolic mirror 32 as parallel light again, and the light beam is focused on the disk crystal 5 for the second time, completing the secondary pumping. After passing through the first parabolic mirror 31 again, it is reflected back to the first parabolic mirror 31 on the second 45° reflector group 41 as parallel light, and the pumping is repeated in this way.

[0034] Furthermore, in order to achieve efficient heat exchange, a disc heat sink 6 is fixed on 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 arranged therein.

[0035] As an optional implementation, the pump module with controllable thermal focal length further includes: a measurement module and a light intensity adjustment module.

[0036] 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, 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, and the light intensity value of each area on the laser crystal at this time is obtained.

[0037] 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.

[0038] The working principle of a pump module with controllable thermal focal length provided by the present invention is described below.

[0039] When the surface shape of the disk crystal is known, the temperature distribution on the disk crystal is measured with the help of reference light, using a thermal imager and an interferometer or a wavefront sensor, and the optical path difference of each measurement point on the disk crystal is obtained with the help of software. Thermal simulation is performed using COMSOL Multiphysics finite element analysis software to obtain a pump light intensity distribution that can meet the change in the focal length of the thermal lens. According to the obtained light intensity distribution result, the light spots of each point light source in the light source module 10 are adjusted to present the light intensity distribution obtained by the simulation.

[0040] 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.

[0041] 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 disk crystal. When the output light of the light source module 10 increases to a pump power that meets the pump power density, the output light at a certain moment is measured. 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 measuring point on the disk crystal is deduced. In this example, 10 kW / cm 2 The pump power density is .

[0042] 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 central 4×4 area, and the optical path difference of each point in the central 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 into 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 . In addition, there is a relationship between the optical path differences of various regions: .

[0043] 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. The maximum value of .

[0044] Combined with software analysis, we need to get Figure 3 The laser diode array light intensity distribution diagram that can make the optical path difference of each point on the disk crystal consistent is shown as type M. According to the adjustment requirements, a 10x10 laser diode array is selected, and the output parameters of each laser diode in the laser diode array are adjusted. The size is represented by the gray level, which increases first and then decreases from the inside to the outside.

[0045] 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 lens 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.

[0046] 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 .

[0047] Alternatively, a semiconductor laser 11 is used as a pump light source, and the beam shaping mirror 12 is a microlens array. By adjusting the parameters of each microlens on the microlens array, the light spot of the light beam emitted through the microlens has the light intensity distribution of the simulation result. In this embodiment, each light beam emitted through the microlens can be considered to be equivalent to a point light source. By changing the position or shape of each microlens, the output light beam has different power values, so that multiple irradiation areas with different light intensities are formed on the laser crystal, and the optical path difference of each irradiation area on the laser crystal is consistent.

[0048] Embodiment 2: The present invention also provides a device embodiment that is consistent with the above embodiment. The explanation based on the same name meaning is the same as the above embodiment, and has the same technical effect as the above embodiment, which will not be repeated here.

[0049] The present invention discloses a disk laser, comprising: a pump module with controllable thermal focal length.

[0050] Embodiment 3: The present invention also provides a device embodiment that is consistent with the above embodiment. The explanation based on the same name meaning is the same as the above embodiment, and has the same technical effect as the above embodiment, which will not be repeated here.

[0051] The invention discloses a disk laser amplifier, comprising a pump module with controllable thermal focal length.

[0052] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the system or device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0053] 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, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. 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 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 of laser crystal; A light source module, wherein the light source module comprises a plurality of light sources arranged in a matrix, wherein the plurality of light sources arranged in a matrix respectively form a plurality of irradiation areas on the laser crystal, and the power of the plurality of light sources arranged in a matrix is ​​adjusted to make the optical path difference of each irradiation area on the laser crystal consistent; The collimation module is used to collimate the outgoing light beam of the light source module.

2. The thermal focus controllable pump module according to claim 1, characterized in that: The light source module comprises: 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.

3. The pump module with controllable thermal focus according to claim 2, characterized in that: The beam shaping mirror comprises: a microlens array, a fly-eye lens or an M-type beam shaping mirror.

4. The thermal focus controllable pump module according to claim 1, characterized in that: The light source module is a laser diode array. The powers of the laser diodes in the laser diode array are different, so that the outgoing light beam forms a plurality of irradiation areas on the laser crystal, and the light intensity value of each irradiation area is different.

5. The thermal focus controllable pump module according to claim 1, characterized in that: The multi-pass coupling cavity comprises: a 4f optical system and a laser crystal module. 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.

6. The pump module with controllable thermal focus according to claim 2 or 4, characterized in that: Also includes: The measuring 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.

7. The pump module with controllable thermal focus according to claim 6, characterized in that: Also includes: 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.

8. The thermal focus controllable pump module according to claim 7, characterized in that: The change in focal length of the thermal lens of the laser crystal is less than 0.005m -1 .

9. A disk laser amplifier, characterized in that: It comprises the pump module with controllable thermal focal length as described in any one of claims 1-8.

10. A disk laser, characterized in that: It comprises the pump module with controllable thermal focal length as described in any one of claims 1-8.

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