A laser resonator active cavity mirror

Abstract

The application discloses an active cavity mirror of a laser resonant cavity, comprising a temperature controller, a pump source and a gain medium microsheet which are sequentially arranged in the temperature controller and cooperated with each other to form the active cavity mirror; the gain medium microsheet comprises a microsheet crystal, one side of the microsheet crystal is provided with a dichromatic film layer corresponding to the pump source, and the other side is provided with a high-reflection film layer. The application integrates the generation function of a single-frequency seed laser and the cavity mirror function of a high-energy laser into a gain medium microsheet assembly to realize self-injection locking of the single-frequency seed light, and simplifies the structure of the seed injection laser while guaranteeing the mode alignment precision and the frequency stability.

Description

Technical Field

[0001] This invention relates to the technical field of all-solid-state lasers, and more particularly to an active cavity mirror for a laser resonator. Background Technology

[0002] Lasers, with their excellent monochromaticity, coherence, directionality, and high brightness, have attracted widespread attention and in-depth research in scientific research, manufacturing, medical diagnosis, and communication detection. Among them, high-energy single-frequency solid-state lasers, with their core advantages of high energy, narrow linewidth, high coherence, and frequency stability, are experiencing a surge in demand in cutting-edge fields such as quantum technology, precision measurement, and lidar.

[0003] Injection locking is a core technology for achieving the "narrow linewidth + high energy + low noise" performance of high-energy single-frequency solid-state lasers. Its principle involves injecting a low-noise single-frequency seed light into the slave laser (slave cavity), forcing the slave laser to lock to the seed light frequency and suppressing other longitudinal modes while maintaining high energy output. The key challenges of this technology lie in the precise control of spatial mode coupling, injection coupling efficiency, and frequency stability.

[0004] The typical features of existing single-frequency seed injection technology include: (1) Spatial mode shaping: Beam expansion, collimation and wavefront correction components are required to ensure that the seed light and the slave laser fundamental mode overlap efficiency is >90% to reduce mode competition; (2) Isolation and polarization control: Faraday isolators are configured to suppress backlight interference, and polarization states of the seed light and the slave laser are matched by polarizers to reduce transmission loss; (3) Frequency locking and feedback control: Active detection feedback tuning methods such as PDH frequency stabilization are used to ensure that the injected seed and the slave cavity longitudinal mode are matched. Based on the current status of laser technology and related patents (such as US5343485A, CN201044323Y), the existing technology can be clearly defined as "laser with seed injection". Its core architecture is that the single-frequency seed light generation module and the high-energy laser module are independent of each other. The seed light needs to be injected into the high-energy laser through an additional optical path (including lenses, isolators and other components).

[0005] The aforementioned split-structure seed injection locking scheme has inherent defects: First, the additional optical path components lead to a complex overall structure of the laser and low integration; second, it is difficult to align the seed light with the spatial mode of the slave cavity and is susceptible to external interference; third, the collaborative operation of multiple components increases the risk of failure, the seed light injection stability is poor, and it is difficult to adapt to the application requirements of extreme environments. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention provides an active cavity mirror for a laser resonator, which simplifies the optical path structure while ensuring mode alignment accuracy and frequency stability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An active cavity mirror for a laser resonator includes a temperature controller. Inside the temperature controller, a pump source and a gain medium microplate are arranged in sequence to form an active cavity mirror. The gain medium microplate includes a microplate crystal. One side of the microplate crystal corresponding to the pump source has a bicolor film layer, and the other side has a high-reflection film layer.

[0008] The dual-color film layer and the high-reflectivity film layer form the resonant cavity of the microchip laser. After the microchip crystal is pumped and stored, a single-frequency seed laser is output from the high-reflectivity film layer.

[0009] Preferably, the pump source is a vertical external cavity surface-emitting laser and integrates a pump light collimating microlens. The center wavelength of the pump source is 808nm, the maximum output power is 1W, and the emitted pump light is focused by the collimating microlens and transmitted to the gain medium microplate. The focused spot radius is about 50μm.

[0010] Preferably, the microcrystal is made of Nd:YAG crystal, Yb:YAG crystal or laser gain material, and has a thickness of 0.3~1mm; Preferably, the dual-color film layer is a dual-color film coated with 1064HR / 808HT, satisfying R(1064nm, 0°)≥99.8% and T(808nm, 0°)≥99%; Preferably, the back surface film is a high reflectance film coated with 1064HR, satisfying R(1064nm, 0°)=99%.

[0011] Preferably, the temperature controller includes a copper heat sink with a channel that runs through both ends. The pump source and the gain medium microchip are respectively placed at both ends of the channel. The dual-color film layer is close to the pump source. The copper heat sink has an assembly hole near the microchip crystal. A temperature sensor is installed in the assembly hole. A semiconductor cooling element is provided at the end of the copper heat sink used to install the pump source. The hot side of the semiconductor cooling element is provided with a heat sink.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention integrates the generation function of a single-frequency seed laser with the resonant cavity mirror function of a high-energy laser into a gain medium microchip assembly, thereby achieving self-injection locking of the single-frequency seed light. While simplifying the structure of the seed injection laser, it also ensures mode alignment accuracy and frequency stability. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the active cavity mirror of the laser resonator in an embodiment of the present invention; Figure 2 This is a schematic diagram of the assembly between the temperature controller, pump source, and gain medium microplate of the present invention; Figure 3This is a schematic diagram of the optical path structure of the active cavity mirror of the present invention applied to a high-energy laser; Figure 4 This is the output spectrum of a solid-state laser using a common high-reflectivity cavity mirror; Figure 5 This is the output spectrum of a solid-state laser using the active cavity mirror of this invention.

[0014] Figure labels: 1. Pump source, 2. Gain medium microplate, 21. Front surface of the dual-color film, 22. Microplate crystal, 23. Back surface of the high-reflectivity film, 3. Temperature controller, 31. Copper heat sink, 32. Temperature sensor, 33. Semiconductor cooling device, 34. Heat sink, 4. Active cavity mirror, 5. Laser crystal, 6. Output cavity mirror. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0016] Example like Figure 1 The laser resonator active cavity mirror 4 shown includes a temperature controller 3. Inside the temperature controller 3, a pump source 1 and a gain medium microplate 2 are arranged in sequence to form the active cavity mirror 4. The gain medium microplate 2 includes a microplate crystal 22. One side of the microplate crystal 22 corresponding to the pump source 1 is provided with a bicolor film layer 21, and the other side is provided with a high-reflection film layer 23. The pump source 1 is a vertical external cavity surface emitter laser and integrates a pump light collimating microlens.

[0017] In practice, the pump light emitted from pump source 1 is transmitted to gain medium microplate 2 via a coupler (pump light collimating microlens) for pumping to output a single-frequency seed laser. Specifically, the dichroic film layer 21 and the high-reflectivity film layer 22 form a microplate laser resonant cavity. After being pumped and energized, the microplate crystal 22 outputs a single-frequency seed laser from the high-reflectivity film layer 23. The temperature controller 3 precisely controls the temperature of the gain medium microplate 2 to ensure the stability of the single-frequency seed laser wavelength.

[0018] When this active cavity mirror is applied to high-energy lasers, such as... Figure 3 As shown, the active cavity mirror 4, together with the laser crystal 5 and the output cavity mirror 6 of the high-energy laser, form a complete resonant cavity. The single-frequency seed laser generated by the active cavity mirror is injected into the resonant cavity to achieve wavelength locking, and finally outputs a single-frequency high-energy laser.

[0019] The pump source 1, which integrates a pump light collimating microlens, can directly transmit pump light to the gain medium microplate 2 without the need for additional lens components. Furthermore, the radius of the pump focusing spot formed inside the gain medium microplate 2 is smaller than the radius of the laser fundamental mode, thereby ensuring the stable generation of single-frequency seed laser.

[0020] The structure of the temperature controller 3 is shown in the figure. It includes a copper heat sink 31 with a channel extending through both ends. The pump source 1 and the gain medium microchip 2 are respectively placed at the two ends of the channel. The dual-color film layer 21 is close to the pump source 1. The copper heat sink 31 has a mounting hole near the microchip crystal 22, and a temperature sensor 32 is installed in the mounting hole. A semiconductor cooler 33 is provided at the end of the copper heat sink 31 where the pump source 1 is installed. The hot side of the semiconductor cooler 33 is provided with a heat sink 34. The semiconductor cooler 33 and the temperature sensor 32 are both connected to a closed-loop feedback control system. In operation, the temperature sensor 32 accurately measures the temperature of the microchip crystal 22 and feeds it back to the control system. The control system regulates the temperature of the copper heat sink 31 by controlling the semiconductor cooler 33, thereby regulating the temperature of the gain medium microchip 2. The temperature change accuracy of the gain medium microchip 2 is better than 0.1℃.

[0021] The active cavity mirror for a laser resonator disclosed in this invention includes the following working process: 1. Pumping and seed light generation process: Pump source 1 (including pump light coupler) outputs pump light, which is collimated and coupled to be incident perpendicularly onto the front surface 21 of the dichroic film. The pump light is efficiently transmitted into the microchip crystal 22 to achieve population inversion. The front surface 21 of the dichroic film and the rear surface 23 of the high reflectivity film constitute the resonant cavity of the microchip laser, which satisfies the laser oscillation condition and forms a single longitudinal mode oscillation inside the microchip. Finally, a single-frequency seed laser is output from the rear surface 23 of the high reflectivity film.

[0022] 2. Self-injection locking process: The active cavity mirror 4 directly serves as a cavity mirror of the high-energy laser resonator. Its output single-frequency seed laser is self-injected into the high-energy laser resonator along the optical axis of the resonator. The seed light is naturally coaxial with the fundamental mode of the high-energy laser crystal, realizing automatic mode alignment with an overlap efficiency of nearly 100%, thus completely solving the problem of difficult mode alignment in traditional schemes.

[0023] 3. Temperature control and frequency stabilization process: Temperature controller 3 implements high-precision closed-loop temperature control on microcrystal 22, suppresses thermally induced wavelength drift, and ensures that the seed light frequency is continuously and accurately matched with the longitudinal mode of the high-energy laser resonator cavity. This fundamentally improves the system's frequency stability and anti-interference capability, solving the problems of poor stability and susceptibility to environmental disturbances in traditional solutions.

[0024] In this embodiment, the pump source 1 is a vertical external cavity surface-emitting laser (VECSEL), which integrates a pump light collimating microlens (i.e., a pump light coupler) in its external cavity. The pump source is electrically connected to an external driving power supply. The center wavelength of the pump source is 808nm, and the maximum output power is 1W. The emitted pump light is focused by the collimating microlens and then transmitted to the gain medium microplate 2. The radius of the focused spot is about 50μm, which is smaller than the radius of the laser fundamental mode, providing the basic conditions for the generation of single-frequency seed laser.

[0025] The specific parameters of the gain medium microchip 2 are as follows: the microchip crystal 22 is an Nd:YAG crystal with a doping concentration of 2%, a light-transmitting area size of Φ3mm, and a length of 0.5mm; the front surface film 21 is coated with a 1064HR / 808HT dual-color film, satisfying R(1064nm, 0°)≥99.8% and T(808nm, 0°)≥99%; the rear surface film 23 is coated with a 1064HR high-reflection film, satisfying R(1064nm, 0°)=99%; the front surface film 21 and the rear surface film 23 form the microchip laser resonant cavity, and after the microchip crystal 22 is pumped and stored, a single-frequency seed laser is output from the rear surface film 23.

[0026] The temperature controller 3 uses a Φ20mm×10mm copper heat sink 31, paired with a Φ20mm / Φ10mm toroidal semiconductor cooler 33, and a high-precision NTC temperature sensor 32. The gain dielectric microchip 2 is welded to the copper heat sink, and the temperature sensor 32 is mounted close to the microchip crystal 22. The semiconductor cooler 33 and the temperature sensor 32 are connected to a closed-loop feedback control system. The control system compares the temperature signal of the microchip crystal 22 collected in real time by the temperature sensor 32 with the 25℃ setpoint, and quickly adjusts the cooling / heating power of the semiconductor cooler 33 using a PID algorithm to stabilize the temperature of the microchip crystal 22 at 25℃±0.1℃. This temperature control accuracy is better than 0.1℃, effectively suppressing the influence of thermal drift on the seed laser wavelength.

[0027] Application examples See Figure 3 When the active cavity mirror 4 of this invention is applied to a high-energy laser, it together with the laser crystal 5 and the output cavity mirror 6 of the high-energy laser to form a complete resonant cavity. Among them, the micro-crystal 22 of the active cavity mirror 4 and the laser crystal 5 are made of the same Nd:YAG laser gain material to ensure mode matching compatibility. The single-frequency seed laser generated by the active cavity mirror 4 is directly injected into the resonant cavity and propagates along the optical axis of the resonant cavity. It is naturally aligned with the mode of the high-energy laser crystal. Through mode competition, the high-energy laser is forced to lock to the seed laser frequency, thereby achieving stable single-frequency output.

[0028] In this application example, the laser crystal 5 of the high-energy laser is a side-pumped Nd:YAG crystal rod with a diameter of 2mm and a diameter of 63.5mm, and the output cavity mirror 6 is an output coupling mirror with a reflectivity of 50%. Based on the above parameters, the laser finally achieves a single longitudinal mode laser output with an average power of 5W and a beam quality of M²=1.3.

[0029] Verification Example To verify the effectiveness of this invention, the laser output spectra of lasers using a conventional high-reflectivity cavity mirror and the active cavity mirror of this invention were compared and measured: see [link / reference]. Figure 4-5 , Figure 4 When using a conventional high-reflectivity cavity mirror, the output spectrum exhibits significant multi-longitudinal mode beat frequency modulation, with noticeable jitter in the center wavelength and morphology. Figure 5 When the active cavity mirror of the present invention is used, the output spectrum exhibits a smooth single-peak shape and the center wavelength is stable without jitter, proving that the present invention can achieve stable single-longitudinal-mode laser output.

[0030] This invention addresses the technical pain points of traditional seed-injection locked lasers—namely, difficulty in mode alignment, weak anti-interference, low integration, and poor stability—through three core technologies: microchip-cavity mirror integration, pump-coupling integration, and high-precision closed-loop temperature control of microchips. It achieves breakthrough improvements in alignment accuracy, environmental adaptability, and cost control, and can broadly expand the application scenarios of single-frequency high-energy lasers in extreme environments.

[0031] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. An active cavity mirror for a laser resonator, characterized in that, The device includes a temperature controller (3), which has a pump source (1) and a gain medium microplate (2) arranged in sequence to form an active cavity mirror (4). The gain medium microplate (2) includes a microplate crystal (22). The microplate crystal (22) has a bicolor film layer (21) on one side corresponding to the pump source (1) and a high-reflectivity film layer (23) on the other side. The bicolor film layer (21) and the high-reflectivity film layer (23) form a microplate laser resonant cavity. After being pumped and stored, the microplate crystal (22) outputs a single-frequency seed laser from the high-reflectivity film layer (23).

2. The active cavity mirror for a laser resonator according to claim 1, characterized in that, The pump source (1) is a vertical external cavity surface-emitting laser and integrates a pump light collimating microlens. The center wavelength of the pump source is 808nm and the maximum output power is 1W. The emitted pump light is focused by the collimating microlens and transmitted to the gain medium microplate (2). The focused spot radius is about 50μm.

3. The active cavity mirror for a laser resonator according to claim 2, characterized in that, The microcrystal (22) is made of Nd:YAG crystal, Yb:YAG crystal or laser gain material, and has a thickness of 0.3~1m.

4. The active cavity mirror for a laser resonator according to claim 3, characterized in that, The dual-color film layer (21) is a dual-color film coated with 1064HR / 808HT, satisfying R(1064nm, 0°)≥99.8% and T(808nm, 0°)≥99.

5. The active cavity mirror for a laser resonator according to claim 3, characterized in that, The back surface film (23) is a high reflectance film with 1064 HR, satisfying R(1064 nm, 0°) = 99%.

6. The laser resonator active cavity mirror according to any one of claims 1-5, characterized in that, The temperature controller (3) includes a copper heat sink (31), which has a channel that runs through both ends. The pump source (1) and the gain medium microplate (2) are respectively placed at both ends of the channel. The dual-color film layer (21) is close to the pump source (1). The copper heat sink (31) has an assembly hole near the microplate crystal (22). A temperature sensor (32) is provided in the assembly hole. A semiconductor cooling element (33) is provided at one end of the copper heat sink (31) for mounting the pump source (1). A heat sink (34) is provided on the hot side of the semiconductor cooling element (33).

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