Device for measuring thermal depolarization rate of side pump solid laser amplifier and test method

Abstract

The invention relates to a device for measuring the thermal depolarization rate of a side pump solid laser amplifier and a testing method, belongs to the technical field of solid lasers, and aims to solve the problem of testing the influence of the thermal depolarization effect on the performance of a laser in the prior art. Comprising a seed light source, a beam expanding system, a first half-wave plate, a first PBS, an amplifier to be tested, a second half-wave plate, a second PBS and an energy meter which are sequentially arranged along the axis. The thermal depolarization rate is determined by accurately controlling the polarization state and measuring the energy ratio before and after depolarization. The device is simple in design and convenient to operate, can effectively improve the measurement precision, is suitable for laser amplifiers of crystal bars of different sizes, and has important significance for improving the performance and the application effect of a laser.

Description

Technical Field

[0001] The invention relates to a device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier and a testing method thereof, belonging to the technical field of solid-state lasers. Background Art

[0002] When the side-pumped solid-state laser amplifier is working, the pumping light of the laser diode (LD) array will generate heat inside the solid-state laser working material, which will cause a variety of thermal effects, including thermal depolarization. The thermal depolarization effect refers to the change in the polarization direction of the laser output light due to thermal stress birefringence caused by the temperature gradient distribution. This phenomenon will reduce the quality of the laser beam and affect the performance and application effect of the laser.

[0003] The mechanism of thermal depolarization is mainly due to the uneven temperature distribution inside the laser working material, which leads to thermal expansion and changes in the thermally induced refractive index, thus forming a thermal lens effect and thermal stress birefringence effect inside the laser crystal. These effects will cause the mode and polarization state of the laser beam to change, especially under high-power pumping conditions.

[0004] The thermal depolarization effect of the side-pumped solid-state amplifier mainly affects the performance parameters of the laser, including beam quality, power, efficiency, and in severe cases, it may even damage the optical components. Depolarization will cause the polarization direction of the laser output to change, thereby affecting the quality and stability of the beam and reducing the output beam quality of the laser. The non-uniform temperature distribution caused by the thermal effect will cause the thermal lens effect and thermally induced birefringence effect inside the laser medium, reducing the gain and output power of the laser.

[0005] There is currently no corresponding testing method for thermal depolarization rate. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a device and a test method for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier, which uses a half-wave plate and a polarizing prism (PBS) to select light of different polarization states, and calculates the ratio of the power after depolarization to the power before depolarization as the thermal depolarization rate. The measuring device is simple, the method is simple, and the difficulty of measuring the thermal depolarization rate is reduced.

[0007] The technical solution of the present invention is as follows:

[0008] A device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier comprises a seed light source, a beam expansion system, a first half-wave plate, a first PBS, an amplifier to be measured, a second half-wave plate, a second PBS and an energy meter which are sequentially arranged along an axis;

[0009] The function of the first half-wave plate is to compensate the polarization state of the seed light source. After compensation, it is selected by the first PBS to ensure that the incident seed light source is a pure linear polarized beam.

[0010] The function of the first half-wave plate is to compensate the polarization state of the seed light. After compensation, it is polarized by PBS to ensure that the incident seed light is a pure linear polarized beam.

[0011] The amplifier to be tested includes an LD array and a crystal rod. The thermal stress birefringence caused by the temperature gradient distribution of the crystal causes the polarization direction of the laser output light to change. The second half-wave plate and the second PBS are used to separate the beams of different polarization states after the amplifier is depolarized.

[0012] Design principle: Isotropic laser crystals will produce optical anisotropy under temperature gradients, and birefringence will occur after linearly polarized light is incident. For two beams of light with perpendicular polarization directions, due to different refractive indices, an optical path difference will be generated after passing through the laser crystal, and after exiting, the light will become elliptically polarized light, resulting in a depolarization effect. The essence of measuring the thermal depolarization effect is to measure the change in the polarization characteristics of the laser.

[0013] Preferably, the seed light source generally uses a fundamental mode light spot with high energy density and good beam quality.

[0014] Preferably, the beam expansion system includes a concave mirror and a convex lens. According to the crystal size of the laser to be tested and the spot size of the seed light, the concave mirror and the convex mirror with appropriate focal lengths are selected, the concave mirror is close to the laser, and the convex lens is close to the amplifier to be tested; the selection of the focal lengths of the two lenses depends on the crystal diameter size of the amplifier.

[0015] The seed light source is generally a fundamental mode light spot with good beam quality. For amplifier modules with large crystal rod diameters, the seed light needs to be expanded. The expansion multiple is the convex mirror focal length / concave mirror focal length. The diameter of the seed light source after expansion by the beam expansion system is 80% of the diameter of the amplifier crystal rod to be tested. The seed light source is expanded by matching concave and convex mirrors with different focal lengths.

[0016] Preferably, the amplifier to be tested is placed on an optical platform.

[0017] Preferably, both surfaces of the first PBS and the second PBS are coated with anti-reflection films.

[0018] A method for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier based on the above-mentioned device comprises the following steps:

[0019] (1) According to the size of the amplifier crystal rod to be tested and the spot size of the seed light source, a concave mirror and a convex lens are selected to form a beam expansion system;

[0020] (2) placing the first half-wave plate and the first PBS behind the beam expansion system in sequence;

[0021] (3) Place the amplifier to be tested on an optical platform, adjust the optical platform so that the seed light source and the end face of the crystal rod are concentric, ensure that the seed light is evenly irradiated to the end face of the crystal, power on the amplifier to be tested, and increase the current to the specified working current;

[0022] (4) Record the energy meter reading, which is the total energy;

[0023] (5) Place the second half-wave plate and the second PBS behind the amplifier to be tested;

[0024] (6) Power on the amplifier to be tested, increase the current to the specified operating current, record the reading on the energy meter at this time, record it as the energy after depolarization, and calculate the thermal depolarization rate:

[0025] Thermal depolarization rate = 1-energy after depolarization / total energy.

[0026] Preferably, in step (2), the first half-wave plate is rotated until the energy transmitted through the first half-wave plate is maximum;

[0027] The first PBS is placed behind the first half-wave plate, and the mirror surface of the first PBS is perpendicular to the optical axis of the seed light source. The seed light source is divided into p-light and s-light.

[0028] Preferably, in step (5), the second half-wave plate is rotated until the energy transmitted through the second half-wave plate is maximum.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention utilizes two groups of half-wave plates and PBS to obtain pure linear polarized light, thereby improving the accuracy of the test.

[0031] 2. The beam expansion multiples of the present invention can be obtained by using different concave mirrors and convex mirrors to obtain different expansion multiples. It has a wide range of applications and is suitable for crystal rods of various sizes, which is of great significance for improving laser performance and application effects.

[0032] 3. The present invention uses a half-wave plate and a polarizing prism (PBS) to select light of different polarization states and calculate the thermal depolarization rate. The measuring device is simple and the method is simple, which reduces the difficulty of measuring the thermal depolarization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0034] Figure 1 It is a schematic diagram of a device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to the present invention;

[0035] In the figure: 1-seed light source, 2-beam expansion system, 3-first half-wave plate, 4-first PBS, 5-amplifier to be tested, 6-second half-wave plate, 7-second PBS, 8-energy meter. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described, but not limited to this. Anything not fully described in the present invention shall be based on conventional techniques in the art.

[0037] Example 1

[0038] A device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier comprises a seed light source 1, a beam expansion system 2, a first half-wave plate 3, a first PBS 4, an amplifier to be measured 5, a second half-wave plate 6, a second PBS 7 and an energy meter 8 which are sequentially arranged along an axis;

[0039] The function of the first half-wave plate 3 is to compensate the polarization state of the seed light source, and after compensation, the first PBS 4 is selected to ensure that the incident seed light source 1 is a pure linear polarized light beam;

[0040] The first half-wave plate 3 is used to compensate the polarization state of the seed light. After compensation, the first PBS is used for polarization selection to ensure that the incident seed light is a pure linear polarization beam.

[0041] The amplifier to be tested 5 includes an LD array and a crystal rod. The thermal stress birefringence caused by the temperature gradient distribution of the crystal causes the polarization direction of the laser output light to change. The second half-wave plate 6 and the second PBS 7 are used to separate the beams of different polarization states after the amplifier is depolarized.

[0042] Design principle: Isotropic laser crystals will produce optical anisotropy under temperature gradients, and birefringence will occur after linearly polarized light is incident. For two beams of light with perpendicular polarization directions, due to different refractive indices, an optical path difference will be generated after passing through the laser crystal, and after exiting, the light will become elliptically polarized light, resulting in a depolarization effect. The essence of measuring the thermal depolarization effect is to measure the change in the polarization characteristics of the laser.

[0043] The seed light source 1 generally uses a fundamental mode light spot with high energy density and good beam quality.

[0044] The beam expansion system 2 includes a concave mirror and a convex lens. According to the crystal size of the laser to be tested and the spot size of the seed light, the concave mirror and convex mirror with appropriate focal length are selected. The concave mirror is close to the laser and the convex lens is close to the amplifier to be tested. The selection of the focal length of the two lenses depends on the crystal diameter size of the amplifier.

[0045] The seed light source is generally a fundamental mode light spot with good beam quality. For amplifier modules with large crystal rod diameters, the seed light needs to be expanded. The expansion multiple is the convex mirror focal length / concave mirror focal length. The diameter of the seed light source after expansion by the beam expansion system is 80% of the diameter of the amplifier crystal rod to be tested. The seed light source is expanded by matching concave and convex mirrors with different focal lengths.

[0046] The amplifier 5 to be tested is placed on an optical platform.

[0047] Anti-reflection films are coated on both sides of the first PBS 4 and the second PBS 7 .

[0048] Example 2

[0049] A method for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier based on the device of embodiment 1 comprises the following steps:

[0050] (1) According to the size of the crystal rod of the amplifier to be tested 5 and the spot size of the seed light source 1, a concave mirror and a convex lens are selected to form a beam expansion system; the diameter of the seed light after beam expansion is 80% of the diameter of the amplifier crystal, and the beam expansion factor is approximately the focal length of the convex mirror / the focal length of the concave mirror. For example, if the crystal diameter of the amplifier to be tested is 8mm and the seed light source is 1mm, a concave mirror with a focal length of 560mm and a convex mirror with a focal length of 100mm are required. The concave mirror is close to the laser, and the convex mirror is close to the amplifier to be tested.

[0051] (2) Place the first half-wave plate 3 and the first PBS 4 behind the beam expansion system 2 in sequence; rotate the first half-wave plate 3 until the energy transmitted through the first half-wave plate 3 is the largest and the energy meter reading is the largest; place the first PBS 4 behind the first half-wave plate 3, and the mirror surface of the first PBS 4 is perpendicular to the optical axis of the seed light source, and the seed light source is divided into p-light and s-light. Note that after passing through the PBS, the laser in the direction perpendicular to the optical axis is shielded by a light blocking plate.

[0052] (3) Place the amplifier 5 to be tested on an optical platform, adjust the optical platform so that the seed light source and the end face of the crystal rod are concentric, ensure that the seed light is evenly irradiated to the end face of the crystal, power on the amplifier to be tested, and increase the current to the specified working current;

[0053] (4) Record the energy meter reading, which is the total energy;

[0054] (5) placing the second half-wave plate 6 and the second PBS 7 behind the amplifier 5 to be tested, and rotating the second half-wave plate until the energy passing through the second half-wave plate is maximum;

[0055] (6) Power on the amplifier 5 to be tested, increase the current to the specified working current, record the reading of the energy meter at this time, record it as the energy after depolarization, and calculate the thermal depolarization rate:

[0056] Thermal depolarization rate = 1-energy after depolarization / total energy.

[0057] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier, characterized in that: It includes a seed light source, a beam expansion system, a first half-wave plate, a first PBS, an amplifier to be tested, a second half-wave plate, a second PBS and an energy meter which are sequentially arranged along an axis; The function of the first half-wave plate is to compensate the polarization state of the seed light source. After compensation, it is selected by the first PBS to ensure that the incident seed light source is a pure linear polarized beam. The amplifier under test includes an LD array and a crystal rod.

2. The device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 1, characterized in that: The seed light source uses a fundamental mode light spot.

3. The device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 2, characterized in that: The beam expansion system includes a concave mirror and a convex lens, wherein the concave mirror is close to the laser and the convex lens is close to the amplifier to be tested; The diameter of the seed light source after beam expansion by the beam expansion system is 80% of the diameter of the crystal rod of the amplifier to be tested.

4. The device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 3, characterized in that: The amplifier to be tested is placed on an optical platform.

5. The device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 4, characterized in that: Anti-reflection films are coated on both sides of the first PBS and the second PBS.

6. A method for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier based on the device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 5, characterized in that: The steps include: (1) According to the size of the amplifier crystal rod to be tested and the spot size of the seed light source, a concave mirror and a convex lens are selected to form a beam expansion system; (2) placing the first half-wave plate and the first PBS behind the beam expansion system in sequence; (3) Place the amplifier to be tested on an optical platform, adjust the optical platform so that the seed light source and the end face of the crystal rod are concentric, ensure that the seed light is evenly irradiated to the end face of the crystal, power on the amplifier to be tested, and increase the current to the working current; (4) Record the energy meter reading, which is the total energy; (5) Place the second half-wave plate and the second PBS behind the amplifier to be tested; (6) Power on the amplifier to be tested, increase the current to the operating current, record the reading on the energy meter at this time, record it as the energy after depolarization, and calculate the thermal depolarization rate: Thermal depolarization rate = 1-energy after depolarization / total energy.

7. The measuring method of the device for measuring the thermal depolarization rate of a side-pumped solid-state laser amplifier according to claim 6, characterized in that: In step (2), the first half-wave plate is rotated until the energy transmitted through the first half-wave plate is maximum; The first PBS is placed behind the first half-wave plate, and the mirror surface of the first PBS is perpendicular to the optical axis of the seed light source. The seed light source is divided into p-light and s-light.

8. The method for measuring the thermal depolarization rate of the device for measuring the side-pumped solid-state laser amplifier according to claim 6, characterized in that: In step (5), the second half-wave plate is rotated until the energy passing through the second half-wave plate is maximum.

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