A coaxial multi-reflection multi-pass solid laser amplifier with off-axis optical path

Abstract

The application relates to the technical field of solid lasers and their amplification systems, and particularly discloses a multi-pass solid laser amplifier established by a coaxial multi-reflection and off-axis light path, which comprises a casing, a laser gain module, a pump light input module and a cooling assembly, wherein the laser gain module, the pump light input module and the cooling assembly are all installed in the interior of the casing, a coaxial light path module, an off-axis reflection unit and a main control board are further installed in the interior of the casing, and an output window is arranged at one end of the casing. In the application, the amplification efficiency is extremely high: through the combination of the coaxial and off-axis designs, 3-6 effective passes are realized, the pump energy utilization rate is increased by 30%-40%, and the overall amplification efficiency can reach more than 65%; the beam quality is excellent: the multi-pass light path is highly overlapped in the crystal, the gain distribution is effectively smoothed, the spot roundness is increased by 20%, and the wavefront distortion is low; and the structure is compact and stable: the coaxial and small-angle off-axis design is used, the light path is folded compactly, and the anti-interference capability is high.

Description

Technical Field

[0001] This invention relates to the technical field of solid-state lasers and their amplification systems, specifically to a multi-pass solid-state laser amplifier that establishes a coaxial multi-reflection plus off-axis optical path. Background Technology

[0002] Laser amplifiers are used to increase the energy of seed light. Currently, there are two main types of solid-state laser amplifier structures: 1. Single-pass / double-pass amplification: using a linear or V-shaped optical path, the beam passes through the gain medium only once or twice. 2. Traditional multi-pass amplification: to increase the optical path, it typically relies on complex planar mirror arrays or folded cavity structures to achieve multiple passes.

[0003] In practical applications, both of the aforementioned mainstream solid-state laser amplifier structures suffer from the following significant drawbacks: 1. Low energy extraction efficiency: In single-pass or double-pass amplification structures, the interaction distance between the beam and the gain medium is short, making it impossible to fully extract pump energy, resulting in low optical-to-optical conversion efficiency. 2. Complex and unstable structure: Traditional multi-pass amplifiers often have complex optical paths, multiple adjustment dimensions, extremely high requirements for mechanical stability, are difficult to assemble and adjust, and are easily affected by environmental vibrations. 3. Thermal effects: Under high-power pumping, poor beam overlap control can lead to thermal distortion, severely affecting the output beam quality. Summary of the Invention

[0004] The purpose of this invention is to address the problems of low energy utilization in existing solid-state laser amplifiers under single-ended pumping conditions and the complex assembly and adjustment of traditional multi-pass structures. Through innovative optical path design, a highly efficient 3-6 order multi-pass amplification is achieved with a compact structure, and a multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus an off-axis optical path is proposed.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A multi-pass solid-state laser amplifier with coaxial multi-reflection and off-axis optical path establishment includes a housing, a laser gain module, a pump light input module, and a cooling component. The laser gain module, pump light input module, and cooling component are all installed inside the housing. The pump light input module is used to provide a single-ended pump beam to the laser gain module. The cooling component is used to maintain the temperature stability of the gain medium crystal inside the laser gain module. The housing also houses a coaxial optical path module, an off-axis reflection unit, and a main control board. One end of the housing has an output window for exporting the laser beam after multiple gain operations. The coaxial optical path module includes a first and a second reflector arranged coaxially along the optical axis. The first and second reflectors constitute a basic resonant or folding unit, forming a multi-reflection optical path. The off-axis reflection unit is located on the outer optical path of the laser gain module and is used to guide part of the outgoing light back into the gain medium. The pump beam generated by the pump light input module passes through the gain medium crystal at least three times effectively through the coaxial optical path module and the off-axis reflection unit to achieve efficient amplification of the signal light.

[0006] Optionally, the laser gain module is used to amplify the input pump beam signal. The gain medium of the laser gain module is an Nd:YVO4, Nd:YAG or Yb:YAG crystal. The crystal is placed at the center of the optical path. The crystal length is 10mm-60mm. Both ends of the crystal are coated with anti-reflection film or high-reflection film. The doping concentration of the crystal is in the range of 0.5-1.5at.

[0007] Optionally, the first reflector is a high-reflectivity mirror with a reflectivity ≥99.8%, the second reflector is a partially transmissive mirror with a reflectivity of 5%-15%, and the installation angle between the first reflector and the second reflector is 25-30 degrees.

[0008] Optionally, the off-axis reflection unit includes at least two off-axis mirrors, with the incident angle of the two off-axis mirrors set to 3-7 degrees, to complete the deflection and double-pass coincidence of the pump beam.

[0009] Optionally, the pump light input module includes a pump source, an optical fiber coupler, a collimating lens, and an incident window. The pump source, optical fiber coupler, and collimating lens are all installed inside the housing, and the pump power range is 10W-100W.

[0010] Optionally, the cooling assembly includes a copper-based water-cooled base, a thermally conductive interface material, and a cooling channel. The flow rate of the coolant inside the cooling channel is 0.5-2.0 L / min, which is used to control the gain dielectric crystal at 24℃-26℃.

[0011] Optionally, the pump beam generated by the pump source can form a four-way to six-way propagation path after being reflected by the first mirror, the second mirror and two off-axis mirrors, and the optical path difference between each path can be controlled within ±0.5mm.

[0012] Optionally, the pump beam has a beam overlap rate of not less than 85% after passing through the gain medium crystal multiple times, and a phase deviation of less than λ / 20, where λ is the laser wavelength.

[0013] Optionally, the main control board is electrically connected to the pump light input module and the cooling component respectively. The main control board is equipped with a main control system, which can simultaneously adjust the pump power and crystal temperature to complete closed-loop control of output power and beam stability.

[0014] The beneficial effects of this invention are: Extremely high amplification efficiency: By combining coaxial and off-axis amplification, 3-6 effective passes are achieved, pump energy utilization is increased by 30%-40%, and the overall amplification efficiency can reach over 65%.

[0015] 2. Excellent beam quality: The multiple optical paths are highly overlapped inside the crystal, with an overlap rate of >85%, which effectively smooths the gain distribution, improves the roundness of the beam spot by 20%, and reduces wavefront distortion.

[0016] 3. Compact and stable structure: Compared with traditional large multi-channel arrays, this structure utilizes coaxial and small-angle off-axis design, resulting in a compact optical path fold and strong anti-interference capability.

[0017] 4. High adjustment precision: With the help of a closed-loop control system, dynamic locking of optical path and phase can be achieved. Attached Figure Description

[0018] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0019] Figure 1 This is a schematic diagram of the overall structure of a multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path proposed in this invention; Figure 2 This is a diagram showing the connection between the gain module and the pump input in this invention; Figure 3 This is a diagram showing the layout of the coaxial mirror assembly and the off-axis optical path in this invention; Figure 4 This is a schematic diagram of the cooling component in this invention; Figure 5 This is a schematic diagram showing the positions of the water inlet and outlet of the cooling component in this invention; Figure 6 This is a schematic diagram showing the flow direction of the coolant inside the cooling channel in this invention; Figure 7 This is a schematic diagram of the multi-path optical propagation principle in this invention.

[0020] In the diagram: 1. Laser gain module; 3. Collimating lens; 4. First reflector; 5. Second reflector; 6. Off-axis reflector; 7. Cooling assembly; 8. Main control board; 9. Output window; 10. Housing. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Reference Figures 1-7 A multi-pass solid-state laser amplifier with coaxial multi-reflection and off-axis optical path establishment includes a housing 10, a laser gain module 1, a pump light input module, and a cooling component 7. The laser gain module 1, the pump light input module, and the cooling component 7 are all installed inside the housing 10. The pump light input module is used to provide a single-ended pump beam to the laser gain module 1. The cooling component 7 is used to maintain the temperature stability of the gain medium crystal inside the laser gain module 1. The housing 10 also houses a coaxial optical path module, an off-axis reflection unit, and a main control board 8. One end of the housing 10 has an output window 9 for exporting the laser beam after multiple gains. The coaxial optical path module includes a first reflector 4 and a second reflector 5 arranged coaxially along the optical axis. The first reflector 4 and the second reflector 5 constitute a basic resonant or folding unit to form a multi-reflection optical path. The off-axis reflection unit is arranged on the outer optical path of the laser gain module 1 to guide part of the outgoing light back into the gain medium. The pump beam generated by the pump light input module passes through the gain medium crystal at least three times effectively through the coaxial optical path module and the off-axis reflection unit to complete the efficient amplification of the signal light.

[0023] In this embodiment, "coaxial" refers to the physical arrangement of the mirrors along the optical axis, with the light beam traveling back and forth between them; "off-axis" refers to the light beam being reflected back after deviating from the principal optical axis. "Multi-pass" refers to the fact that this embodiment achieves 3-6 passes, which differs from the ordinary two-pass (2-pass) amplification in the prior art.

[0024] The above design has the following significant advantages: 1. Extremely high amplification efficiency: By combining coaxial and off-axis amplification, 3-6 effective passes are achieved, pump energy utilization is increased by 30%-40%, and the overall amplification efficiency can reach over 65%.

[0025] 2. Excellent beam quality: The multiple optical paths are highly overlapped inside the crystal, with an overlap rate of >85%, which effectively smooths the gain distribution, improves the roundness of the beam spot by 20%, and reduces wavefront distortion.

[0026] 3. Compact and stable structure: Compared with traditional large multi-channel arrays, this structure utilizes coaxial and small-angle off-axis design, resulting in a compact optical path fold and strong anti-interference capability.

[0027] 4. High adjustment precision: With the help of a closed-loop control system, dynamic locking of optical path and phase can be achieved.

[0028] As a technical optimization of the present invention, the laser gain module 1 is used to amplify the input pump beam signal. The gain medium of the laser gain module 1 is Nd:YVO4, Nd:YAG or Yb:YAG crystal. The crystal is placed in the center of the optical path. The length of the crystal is 10mm-60mm. Both ends of the crystal are coated with anti-reflection film or high reflection film. The doping concentration of the crystal is in the range of 0.5-1.5at.

[0029] As an optimized technical solution of the present invention, the first reflecting mirror 4 is a high-reflectivity mirror with a reflectivity ≥99.8%, and the second reflecting mirror 5 is a partially transmissive mirror with a reflectivity of 5%-15%. The installation angle between the first reflecting mirror 4 and the second reflecting mirror 5 is 25-30 degrees. The first reflecting mirror 4 and the second reflecting mirror 5 are placed coaxially with an angle of approximately 28°, and the pump beam forms a double-reflection path between the mirror groups.

[0030] As a technical optimization of this invention, the off-axis reflection unit includes at least two off-axis mirrors 6, with the incident angle of the two off-axis mirrors 6 set to 3-7 degrees, used to complete the deflection and double-pass coincidence of the pump beam. The off-axis reflection unit is set on the outer optical path of the laser gain module 1. Its function is to fully concentrate and utilize the beam that is about to escape, allowing it to pass through the crystal again. An off-axis mirror 6 (installation angle 5°) is set on the outer side of the optical path. After the beam undergoes coaxial reflection, part of the beam is intercepted and reflected by the off-axis mirror 6, allowing it to re-enter the crystal, ultimately achieving four-way propagation. Comparison shows that under a pump power of 40W, after the above optical path amplification, the output power reaches 22W. The coincidence rate of the beam passing through the crystal four times reaches 90%, which not only fully utilizes the pump energy but also achieves M 2 High-quality beam with a strength of less than 1.3.

[0031] As an optimized technical solution of the present invention, the pump light input module includes a pump source, an optical fiber coupler, a collimating lens 3, and an incident window. The pump source, optical fiber coupler, and collimating lens 3 are all installed inside the housing 10. The optical fiber coupler is installed at one end of the pump source, and the pump power range is 10W-100W. The pump light is output from the optical fiber coupler, corrected by the collimating lens 4, and then incident on the crystal along the optical axis. In one embodiment, the pump power is 40W, and the output light power reaches 22W; in another embodiment, when the pump power is increased to 80W, the output efficiency is 68%, and the beam quality remains M2 < 1.3 due to multi-pass amplification.

[0032] As an optimized technical solution of the present invention, the cooling component 7 includes a copper-based water-cooled base, a thermally conductive interface material, and a cooling channel. The flow rate of the coolant inside the cooling channel is 0.5-2.0 L / min, used to control the gain dielectric crystal at 24℃-26℃. Figure 4 As shown, the cooling component 7 is located on the upper and lower sides of the laser gain module 1, including a copper-based water-cooled base and a thermally conductive silicone grease layer. The thermally conductive silicone grease layer is located between the copper-based water-cooled base and the laser gain module 1, so that the thermally conductive silicone grease layer can quickly conduct the high temperature generated during the operation of the laser gain module 1 to the inside of the copper-based water-cooled base. The main control board 8 controls the flow rate and temperature of the coolant inside the copper-based water-cooled base, keeping the crystal at 25°C. With the closed-loop feedback of the main control board 8, the laser gain module 1 is ensured to operate stably for a long time.

[0033] As a technical optimization of the present invention, the pump beam generated by the pump source is reflected by the first reflecting mirror 4, the second reflecting mirror 5 and the two off-axis reflecting mirrors 6 to form a four-way to six-way propagation path, and the optical path difference between each path is controlled within ±0.5mm.

[0034] As a technical optimization of the present invention, the beam overlap rate of the pump beam after passing through the gain medium crystal multiple times is not less than 85%, and the phase deviation is less than λ / 20, where λ is the laser wavelength.

[0035] As a technical optimization of the present invention, the main control board 8 is electrically connected to the pump light input module and the cooling component 7 respectively. The main control board 8 is equipped with a preset main control system, which can simultaneously adjust the pump power and crystal temperature to complete the closed-loop control of output power and beam stability. Working Principle: This invention employs a composite optical path strategy of "coaxial multi-reflection + off-axis folding". The pump light is injected into the gain medium at one end. The signal light first undergoes reciprocating reflection between the "coaxial mirror group" arranged along the optical axis (forming a basic multi-path), and then part of the beam is captured and deflected by the "off-axis reflection unit" and re-injected into the gain medium for a new round of amplification. This design cleverly utilizes spatial geometry, significantly increasing the optical path length and gain order without substantially increasing the cavity length.

[0036] Best practice: like Figure 1-7 As shown, the present invention provides a multi-pass solid-state laser amplifier established by coaxial multi-reflection plus off-axis optical path.

[0037] Core optical path layout: 1. Gain medium: Nd:YAG crystal (30mm in length) is selected.

[0038] 2. Coaxial optical path: The first reflecting mirror 4 and the second reflecting mirror 5 are placed coaxially along the optical axis of the crystal, with the included angle set at approximately 28° (this angle needs to be finely adjusted according to the actual optical path design to form a fold). The beam forms a preliminary reciprocating path between these two mirrors.

[0039] 3. Off-axis optical path: An off-axis reflector 6 (installation angle 5°) is set on the outside of the optical path. After the beam is reflected coaxially, part of the beam is intercepted and reflected by the off-axis reflector 6, allowing it to re-enter the crystal and ultimately achieve four-way propagation. Performance: Under a pump power of 40W, the output power reaches 22W after amplification via the aforementioned optical path. The overlap rate of the beams passing through the crystal four times reaches 90%, which not only fully utilizes the pump energy but also achieves M... 2 High-quality beam with a strength of less than 1.3.

[0040] Temperature control: Cooling component 7 keeps the crystal at 25℃, and in conjunction with the closed-loop feedback of main control board 8, ensures stable operation over a long period of time.

[0041] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A multi-pass solid-state laser amplifier with coaxial multi-reflection and off-axis optical path establishment, comprising a housing (10), a laser gain module (1), a pump light input module, and a cooling assembly (7), characterized in that, The laser gain module (1), pump light input module and cooling component (7) are all installed inside the housing (10). The pump light input module is used to provide a single-ended pump beam to the laser gain module (1). The cooling component (7) is used to maintain the temperature stability of the gain medium crystal inside the laser gain module (1). The housing (10) is also equipped with a coaxial optical path module, an off-axis reflection unit and a main control board (8). One end of the housing (10) is provided with an output window (9) for exporting the laser beam after multiple gains. The coaxial optical path module includes a first reflector (4) and a second reflector (5) arranged coaxially along the optical axis. The first reflector (4) and the second reflector (5) constitute a basic resonant or folding unit to form a multi-reflection optical path. The off-axis reflection unit is set on the optical path outside the laser gain module (1) to guide part of the outgoing light back into the gain medium. The pump beam generated by the pump light input module passes through the gain medium crystal at least three times under the combined action of the coaxial optical path module and the off-axis reflection unit to complete the efficient amplification of the signal light.

2. The multi-pass solid-state laser amplifier established by coaxial multi-reflection and off-axis optical paths according to claim 1, characterized in that, The laser gain module (1) is used to amplify the input pump beam signal. The gain medium of the laser gain module (1) is Nd:YVO4, Nd:YAG or Yb:YAG crystal. The crystal is placed in the center of the optical path. The length of the crystal is 10mm-60mm. Both ends of the crystal are coated with anti-reflection film or high-reflection film. The doping concentration of the crystal is in the range of 0.5-1.5at.

3. The multi-pass solid-state laser amplifier established by coaxial multi-reflection and off-axis optical paths according to claim 1, characterized in that, The first reflector (4) is a high-reflectivity mirror with a reflectivity ≥99.8%, and the second reflector (5) is a partial-transmission mirror with a reflectivity of 5%-15%. The installation angle between the first reflector (4) and the second reflector (5) is 25-30 degrees.

4. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in claim 1, characterized in that, The off-axis reflection unit includes at least two off-axis mirrors (6), and the incident angle of the two off-axis mirrors (6) is set to 3-7 degrees to complete the deflection and double-pass coincidence of the pump beam.

5. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in claim 1, characterized in that, The pump light input module includes a pump source, an optical fiber coupler, a collimating lens (3) and an incident window. The pump source, optical fiber coupler and collimating lens (3) are all installed inside the housing (10), and the pump power range is 10W-100W.

6. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in claim 1, characterized in that, The cooling component (7) includes a copper-based water-cooled base, a thermally conductive interface material, and a cooling channel. The flow rate of the coolant inside the cooling channel is 0.5-2.0 L / min, which is used to control the gain medium crystal at 24℃-26℃.

7. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in any one of claims 1-6, characterized in that, The pump beam generated by the pump source is reflected by the first reflector (4), the second reflector (5) and two off-axis reflectors (6) to form a four-way to six-way propagation path, and the optical path difference between each path is controlled within ±0.5mm.

8. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in claim 7, characterized in that, The pump beam has a beam overlap rate of no less than 85% after passing through the gain medium crystal multiple times, and a phase deviation of less than λ / 20, where λ is the laser wavelength.

9. A multi-pass solid-state laser amplifier based on a coaxial multi-reflector plus off-axis optical path as described in claim 1, characterized in that, The main control board (8) is electrically connected to the pump light input module and the cooling component (7) respectively. The main control board (8) is equipped with a main control system, which can simultaneously adjust the pump power and crystal temperature to complete the closed-loop control of output power and beam stability.

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