A single-frequency continuous-wave tunable alexandrite laser

Abstract

The application discloses a single-frequency continuous wave tunable tsavorite laser, relates to the technical field of tsavorite lasers, and comprises a first pump light path, a second pump light path, a first laser crystal, a second laser crystal and a laser resonant cavity; the two pump light paths are used for cross-injection of the split pump light to four end faces of the two crystals, the polarization adjusting elements are used for equalizing the power of the four-end-face incident pump light and making the polarization directions of the four-end-face incident pump light meet the optimal absorption polarization direction of the tsavorite crystal; the laser resonant cavity is provided with a etalon locking feedback system and a cavity length adjusting element; the etalon locking feedback system is used for locking the transmission peak of the etalon to the oscillation frequency of the laser resonant cavity; and the cavity length adjusting element is used for realizing the continuous tuning of the laser frequency by changing the cavity length of the laser resonant cavity. The application can realize the uniform pumping of the tsavorite crystal, improve the crystal heat distribution, improve the laser conversion efficiency and output stability, and realize the continuous tuning of the frequency of the single-frequency laser.

Description

Technical Field

[0001] This application relates to the field of alexandrite laser technology, and in particular to a single-frequency continuous-wave tunable alexandrite laser. Background Technology

[0002] All-solid-state single-frequency continuous-wave tunable lasers have the characteristics of narrow linewidth, high frequency stability, excellent beam quality and wavelength tunability, and have important application value in fields such as precision spectroscopy, atomic and molecular physics, lidar, and biomedical imaging.

[0003] Ti:sapphire lasers are a typical type of wide-tunable solid-state laser, possessing a broad gain bandwidth and excellent single-frequency operation characteristics. However, Ti:sapphire crystals typically require pumping with a green laser, resulting in a relatively complex pumping system and higher overall size and maintenance costs. In contrast, alexandrite crystals can achieve tunable laser output in the visible and near-infrared bands and can be directly pumped with semiconductor lasers, offering advantages such as compact pump source structure, high system integration, and strong practicality.

[0004] Aldehyde crystals exhibit significant absorption differences in the polarization direction of pump light, altering the distribution of thermal deposition and the intensity of thermal lensing within the crystal. Furthermore, under high-power end-face pumping, thermal deposition occurs within the aldehyde crystal, creating a non-uniform temperature field that causes refractive index changes and end-face deformation, affecting the laser's conversion efficiency, cavity stability, and output beam quality. Currently, research on single-frequency continuously tunable lasers based on aldehyde crystals is relatively limited, and the continuous tuning structure combining intracavity etalon locking, resonant cavity length adjustment, and feedback control still requires further design and refinement. Summary of the Invention

[0005] The purpose of this application is to provide a single-frequency continuous-wave tunable alexandrite laser that can achieve uniform pumping of alexandrite crystal to improve crystal thermal distribution and enhance laser conversion efficiency and output stability, while simultaneously achieving continuous frequency tuning of the single-frequency laser.

[0006] To achieve the above objectives, this application provides the following solution: This application provides a single-frequency continuous-wave tunable alexandrite laser, comprising: a first pump optical path, a second pump optical path, a first laser crystal, a second laser crystal, and a laser resonant cavity; Both the first and second laser crystals are emerald green crystals, symmetrically arranged within the laser resonant cavity; The first pump optical path includes a first pump source, a first polarization beam splitter, a first focusing group, a second focusing group, a fifth focusing group, and a first beam steering group; the pump light output from the first pump source is collimated by the fifth focusing group and then incident on the first polarization beam splitter, which splits it into a first transmitted light and a first reflected light. The first transmitted light is incident on the first end face of the first laser crystal through the first focusing group, and the first reflected light is redirected by the first beam steering group and then incident on the second end face of the second laser crystal through the second focusing group. The second pump optical path includes a second pump source, a second polarization beam splitter, a third focusing group, a fourth focusing group, a sixth focusing group, and a second beam steering group. The pump light output from the second pump source is collimated by the sixth focusing group and then incident on the second polarization beam splitter. The second polarization beam splitter splits the light into a second transmitted light and a second reflected light. The second transmitted light is incident on the first end face of the second laser crystal through the third focusing group. The second reflected light is redirected by the second beam steering group and then incident on the second end face of the first laser crystal through the fourth focusing group. The first pump optical path has a first polarization adjustment element before the first polarization beam splitter, and the second pump optical path has a second polarization adjustment element before the second polarization beam splitter. By adjusting the first polarization adjustment element and the second polarization adjustment element, the power of the transmitted light and the reflected light after being split by each polarization beam splitter is equal. The first beam steering group is provided with a third polarization adjustment element, and the second beam steering group is provided with a fourth polarization adjustment element. The third polarization adjustment element is used to adjust the polarization direction of the first reflected light to be consistent with the polarization direction of the first transmitted light, and the fourth polarization adjustment element is used to adjust the polarization direction of the second reflected light to be consistent with the polarization direction of the second transmitted light. The adjusted polarization directions both satisfy the optimal absorption polarization direction of the emerald crystal, so that the pump light incident on all end faces of the two laser crystals has equal power and consistent polarization state, forming a dual-crystal gain structure with double-ended symmetrical pumping. The laser resonant cavity is equipped with an etalon locking feedback system and a cavity length adjustment element. The etalon locking feedback system locks the transmission peak of the etalon to the oscillation frequency of the laser resonant cavity, and the cavity length adjustment element achieves continuous tuning of the laser frequency by changing the cavity length of the laser resonant cavity.

[0007] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a single-frequency continuous-wave tunable alexandrite laser. It employs two pump optical paths to cross-pump two alexandrite crystals. Each pump optical path includes a polarization adjustment element, ensuring that the pump light incident on all end faces of the two laser crystals has equal power and a consistent polarization state. This constitutes a dual-crystal gain structure with symmetrical dual-end pumping, thereby achieving uniform pumping of the alexandrite crystals, improving the energy and heat distribution within the crystals, alleviating the problem of uneven thermal deposition caused by the difference between the pump light polarization direction and the crystal's b-axis absorption, and improving the laser's conversion efficiency and output stability. Furthermore, by placing a first polarization adjustment element before the first polarization beam splitter and a second polarization adjustment element before the second polarization beam splitter, this application achieves balanced adjustment of the transmitted and reflected light power after beam splitting by each polarization beam splitter, ensuring equal power of the incident pump light at both ends, further improving the accuracy and pump light utilization efficiency of symmetrical dual-end pumping. This application incorporates a third polarization adjustment element in the first beam steering group and a fourth polarization adjustment element in the second beam steering group. This adjusts the polarization direction of the reflected light to match that of the transmitted light, ensuring that the polarization direction of all pump light incident on the crystal end face satisfies the optimal absorption polarization direction of the emerald crystal, thus maximizing the crystal's absorption efficiency for the pump light. Furthermore, this application achieves continuous frequency tuning of the single-frequency laser by incorporating an etalon-locked feedback system and a cavity length adjustment element within the laser resonant cavity. The etalon-locked feedback system locks the transmission peak of the etalon to the resonant cavity oscillation frequency, while the cavity length adjustment element changes the cavity length. This ensures continuous tunable output and frequency stability of the laser across a wide wavelength range. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of a single-frequency continuous-wave tunable alexandrite laser provided in an embodiment of this application; Figure 2 This is a schematic diagram of the continuous tuning experiment results provided in an embodiment of this application.

[0010] Figure reference numerals: First pump source and its coupling system-1, Second pump source and its coupling system-2, Laser resonant cavity-3, First laser crystal-4, Second laser crystal-5, First intracavity lens-6, Second intracavity lens-7, Optical one-way mirror-8, Birefringent filter-9, Erebaum-10, Galvanometer motor-11, Piezoelectric ceramic-12, Optical beam splitter-13, Photodetector-14, Servo controller-15, First pump source-1-1, First half-wave plate-1-2, First pump coupling lens-1-3, First polarizing beam splitter-1-4, Second pump coupling lens-1-5, First pump reflector-1-6, Second half-wave plate-1-7, Second pump reflector-1-8, Third pump coupling lens-1-9 Second pump source-2-1, third half-wave plate-2-2, fourth pump coupling lens-2-3, second polarizing beam splitter-2-4, fifth pump coupling lens-2-5, third pump reflector-2-6, fourth half-wave plate-2-7, fourth pump reflector-2-8, sixth pump coupling lens-2-9, first cavity mirror-3-1, second cavity mirror-3-2, third cavity mirror-3-3, fourth cavity mirror-3-4, fifth cavity mirror-3-5, sixth cavity mirror-3-6, first end face of first laser crystal-4-1, second end face of first laser crystal-4-2, first end face of second laser crystal-5-1, second end face of second laser crystal-5-2, natural rotation compensation plate-8-1, permanent magnetic field terbium gallium garnet crystal-8-2. Detailed Implementation

[0011] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0012] The purpose of this application is to improve the pump energy distribution and heat distribution within the crystal, and to provide a single-frequency continuous-wave tunable alexandrite laser to improve laser output performance and operational stability, and to achieve continuous tunability over a wide wavelength range.

[0013] This application provides a single-frequency continuous-wave tunable alexandrite laser, comprising a pump source and its coupling system, a laser resonant cavity 3, an alexandrite crystal, a lens, an optical one-way transducer 8, a birefringent filter 9, an etalon 10, a galvanometer motor 11, a piezoelectric ceramic 12, an optical beam splitter 13, a photodetector 14, and a servo controller 15. This application employs a dual-crystal structure with symmetrical pumping at both ends. Through polarization adjustment and polarization splitting, pump light is incident from opposite ends of the first laser crystal 4 and the second laser crystal 5 with the same polarization state and power, achieving uniform pumping of the dual crystals. Simultaneously, longitudinal mode selection is performed using the intracavity etalon 10, and the cavity length is adjusted in conjunction with the piezoelectric ceramic 12 to achieve continuous tuning of the laser frequency. This application improves the pump light utilization efficiency and enhances the thermal distribution characteristics of the laser crystal by optimizing the pumping method and resonant cavity structure, thus achieving stable single-frequency continuous-wave tunable alexandrite laser output.

[0014] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] In one exemplary embodiment, such as Figure 1 As shown, a single-frequency continuous-wave tunable alexandrite laser is provided, comprising: a first pump optical path, a second pump optical path, a first laser crystal 4, a second laser crystal 5, and a laser resonant cavity 3.

[0016] The first laser crystal 4 and the second laser crystal 5 are both emerald crystals and are symmetrically arranged in the laser resonant cavity 3.

[0017] The first pump optical path includes a first pump source 1-1, a first polarization beam splitter (which may be a first polarization beam splitter prism 1-4 in this embodiment), a first focusing group, a second focusing group, a fifth focusing group, and a first beam steering group; the pump light output from the first pump source 1-1 is collimated by the fifth focusing group and then incident on the first polarization beam splitter, which splits it into a first transmitted light and a first reflected light. The first transmitted light is incident on the first end face 4-1 of the first laser crystal 4 through the first focusing group, and the first reflected light is incident on the second end face 5-2 of the second laser crystal 5 through the second focusing group after the direction is changed by the first beam steering group.

[0018] The second pump optical path includes a second pump source 2-1, a second polarization beam splitter (which may be a second polarization beam splitter prism 2-4 in this embodiment), a third focusing group, a fourth focusing group, a sixth focusing group, and a second beam steering group. The pump light output from the second pump source 2-1 is collimated by the sixth focusing group and then incident on the second polarization beam splitter. The second polarization beam splitter splits the light into a second transmitted light and a second reflected light. The second transmitted light is incident on the first end face 5-1 of the second laser crystal 5 through the third focusing group. The second reflected light is redirected by the second beam steering group and then incident on the second end face 4-2 of the first laser crystal 4 through the fourth focusing group.

[0019] The first pump optical path has a first polarization adjustment element before the first polarization beam splitter, and the second pump optical path has a second polarization adjustment element before the second polarization beam splitter. By adjusting the first polarization adjustment element and the second polarization adjustment element, the power of the transmitted light and the reflected light after being split by each polarization beam splitter is equal.

[0020] The first beam steering group is provided with a third polarization adjustment element, and the second beam steering group is provided with a fourth polarization adjustment element. The third polarization adjustment element is used to adjust the polarization direction of the first reflected light to be consistent with the polarization direction of the first transmitted light, and the fourth polarization adjustment element is used to adjust the polarization direction of the second reflected light to be consistent with the polarization direction of the second transmitted light. The adjusted polarization directions both satisfy the optimal absorption polarization direction of the emerald crystal, so that the pump light incident on all end faces of the two laser crystals has equal power and consistent polarization state, forming a dual-crystal gain structure with double-ended symmetrical pumping.

[0021] The laser resonant cavity 3 is equipped with a standard etalon 10 locking feedback system and a cavity length adjustment element. The standard etalon 10 locking feedback system locks the transmission peak of the standard etalon 10 to the oscillation frequency of the laser resonant cavity 3. The cavity length adjustment element achieves continuous tuning of the laser frequency by changing the cavity length of the laser resonant cavity 3.

[0022] This embodiment provides a single-frequency continuous-wave tunable alexandrite laser. It employs two pump optical paths to cross-pump two alexandrite crystals. Each pump optical path includes a polarization adjustment element, ensuring that the pump light incident on all end faces of the two laser crystals has equal power and a consistent polarization state. This constitutes a dual-crystal gain structure with symmetrical dual-end pumping, thereby achieving uniform pumping of the alexandrite crystals, improving the energy and heat distribution within the crystals, alleviating the problem of uneven thermal deposition caused by the difference in absorption between the pump light polarization direction and the crystal's b-axis, and improving the laser's conversion efficiency and output stability. Furthermore, by placing a first polarization adjustment element before the first polarization beam splitter and a second polarization adjustment element before the second polarization beam splitter, this embodiment achieves balanced adjustment of the transmitted and reflected light power after beam splitting by each polarization beam splitter, ensuring equal power of the incident pump light at both ends, further improving the accuracy and pump light utilization efficiency of symmetrical dual-end pumping. In this embodiment, a third polarization adjustment element is set in the first beam steering group and a fourth polarization adjustment element is set in the second beam steering group. This adjusts the polarization direction of the reflected light to be consistent with the polarization direction of the transmitted light, ensuring that the polarization direction of all pump light incident on the crystal end face satisfies the optimal absorption polarization direction of the emerald crystal, thus maximizing the crystal's absorption efficiency of the pump light. In this embodiment, by setting a etalon 10 locking feedback system and a cavity length adjustment element within the laser resonant cavity 3, the etalon 10 locking feedback system locks the transmission peak of the etalon 10 to the resonant cavity oscillation frequency, and the cavity length adjustment element changes the cavity length, achieving continuous frequency tuning of the single-frequency laser and ensuring continuous tunable output and frequency stability of the laser over a wide wavelength range.

[0023] In another exemplary embodiment of this application, the first focusing group, the second focusing group, the third focusing group, and the fourth focusing group are all pump-coupled lenses; the first pump optical path is further provided with a fifth focusing group before the first polarization beam splitter, for collimating the pump light output from the first pump source 1-1 and then incident it onto the first polarization beam splitter; the second pump optical path is further provided with a sixth focusing group before the second polarization beam splitter, for collimating the pump light output from the second pump source 2-1 and then incident it onto the second polarization beam splitter.

[0024] The first polarization adjustment element, the second polarization adjustment element, the third polarization adjustment element, and the fourth polarization adjustment element are all half-wave plates.

[0025] The pump light output from the first pump source 1-1 passes sequentially through the first polarization adjustment element, the fifth focusing group, and the first polarization beam splitter. The transmitted light from the first polarization beam splitter is incident on the first end face 4-1 of the first laser crystal 4 via the first focusing group. The reflected light from the first polarization beam splitter passes sequentially through the first mirror (which can be selected as the first pump mirror 1-6 in this embodiment), the third polarization adjustment element, the second mirror (which can be selected as the second pump mirror 1-8 in this embodiment), and the second focusing group before being incident on the second end face 5-2 of the second laser crystal 5.

[0026] The pump light output from the second pump source 2-1 passes sequentially through the second polarization adjustment element, the sixth focusing group, and the second polarization beam splitter. The transmitted light from the second polarization beam splitter is incident on the first end face 5-1 of the second laser crystal 5 via the third focusing group. The reflected light from the second polarization beam splitter passes sequentially through the third reflecting mirror (which can be selected as the third pump reflecting mirror 2-6 in this embodiment), the fourth polarization adjustment element, the fourth reflecting mirror (which can be selected as the fourth pump reflecting mirror 2-8 in this embodiment), and the fourth focusing group before being incident on the second end face 4-2 of the first laser crystal 4.

[0027] The first polarization adjustment element is used to adjust the polarization direction of the output beam of the first pump source 1-1 to change the power ratio of the transmitted light to the reflected light of the first polarization beam splitter; the second polarization adjustment element is used to adjust the polarization direction of the output beam of the second pump source 2-1 to change the power ratio of the transmitted light to the reflected light of the second polarization beam splitter.

[0028] In another exemplary embodiment of this application, the laser resonant cavity 3 is a ring resonant cavity; the laser resonant cavity 3 includes a first cavity mirror 3-1, a second cavity mirror 3-2, a third cavity mirror 3-3, a fourth cavity mirror 3-4, a fifth cavity mirror 3-5, and a sixth cavity mirror 3-6.

[0029] The first laser crystal 4 is disposed in the optical path between the first cavity mirror 3-1 and the second cavity mirror 3-2, and the second laser crystal 5 is disposed in the optical path between the first cavity mirror 3-1 and the third cavity mirror 3-3.

[0030] In a clockwise direction, the laser light generated by the stimulated emission of the first laser crystal 4 and the second laser crystal 5 is reflected by the second cavity mirror 3-2 and then passes sequentially through the first intracavity lens 6 and the fifth cavity mirror 3-5. The fifth cavity mirror 3-5 reflects the incident light to the optical one-way mirror 8, and after passing through the optical one-way mirror 8, it enters the sixth cavity mirror 3-6. The sixth cavity mirror 3-6 transmits a portion of the incident light as the output beam of the laser resonant cavity 3, and reflects the other portion to the wavelength tuning element. After being tuned by the wavelength... After frequency selection by the component, the incident light is incident on the fourth cavity mirror 3-4, which reflects the incident light to the etalon 10. After mode selection by the etalon 10, the incident light is incident on the second intracavity lens 7, and then on the third cavity mirror 3-3. The third cavity mirror 3-3 reflects the incident light and passes through the second laser crystal 5 before being incident on the first cavity mirror 3-1. The first cavity mirror 3-1 reflects the incident light and passes through the first laser crystal 4 before being incident on the second cavity mirror 3-2, forming a ring optical path.

[0031] In another exemplary embodiment of this application, the first cavity mirror 3-1, the second cavity mirror 3-2, the third cavity mirror 3-3, the fourth cavity mirror 3-4, the fifth cavity mirror 3-5, and the sixth cavity mirror 3-6 are all planar reflecting mirrors that are tilted at 45° relative to the incident light.

[0032] The first cavity mirror 3-1, the second cavity mirror 3-2 and the third cavity mirror 3-3 are all used to transmit pump light into the laser resonant cavity 3 and to make the laser reflect and oscillate within the cavity. Each cavity mirror is coated with a film layer that is highly transparent to the pump light wavelength and highly reflective to the laser wavelength.

[0033] The fourth cavity mirror 3-4 and the fifth cavity mirror 3-5 are both used to reflect and oscillate the laser within the cavity, and each cavity mirror is coated with a film layer that is highly reflective to the laser wavelength.

[0034] The sixth cavity mirror 3-6 is used to output part of the laser from the cavity and to reflect part of the laser back into the cavity to continue oscillation. The sixth cavity mirror 3-6 is coated with a film layer that transmits part of the laser wavelength.

[0035] In another exemplary embodiment of this application, the first cavity mirror 3-1, the second cavity mirror 3-2 and the third cavity mirror 3-3 are all coated with a film layer that has a transmittance of more than 95% for 638 nm pump light and a reflectance of more than 99.9% for 700 nm to 850 nm laser light.

[0036] Both the fourth cavity mirror 3-4 and the fifth cavity mirror 3-5 are coated with a film layer with a reflectivity greater than 99.9% for lasers in the range of 700 nm to 850 nm.

[0037] The sixth cavity mirror 3-6 is coated with a film layer that has a transmittance of 1% for lasers in the range of 700 nm to 850 nm.

[0038] In another exemplary embodiment of this application, the first pump source 1-1 and the second pump source 2-1 are both semiconductor laser diodes, the center wavelength of the pump light output by the first pump source 1-1 and the second pump source 2-1 is 638 nm, and the first pump source 1-1 and the second pump source 2-1 have the same output power.

[0039] The optical one-way device 8 is disposed in the optical path between the fifth cavity mirror 3-5 and the sixth cavity mirror 3-6. The optical one-way device 8 is used to force the laser in the laser resonant cavity 3 to rotate in a single direction to prevent the spatial hole burning effect. The optical one-way device 8 is composed of a natural optical rotation compensation plate 8-1 and a terbium gallium garnet crystal 8-2 with an external permanent magnetic field. The optical one-way device 8 is placed in the optical path at Brewster angle.

[0040] The wavelength tuning element is disposed in the optical path between the sixth cavity mirror 3-6 and the fourth cavity mirror 3-4. The wavelength tuning element is used to perform coarse wavelength tuning on the laser in the laser resonant cavity 3. The wavelength tuning element is a birefringent filter 9, which is placed in the optical path at Brewster angle. The birefringent filter 9 is made of three pieces of quartz crystal material with parallel optical axes and a thickness ratio of 1:2:4.

[0041] In another exemplary embodiment of this application, the etalon 10 is disposed in the optical path between the fourth cavity mirror 3-4 and the second intracavity lens 7. The etalon 10 is used to perform longitudinal mode selection on the laser in the laser resonant cavity 3 to suppress longitudinal mode oscillations other than the transmission peak center frequency.

[0042] The standard etalon 10 is a fused silica sheet with a thickness of 0.5 mm, and the surface of the standard etalon 10 is coated with a film layer with a reflectivity of 20% for lasers in the range of 700 nm to 850 nm.

[0043] In another exemplary embodiment of this application, the cavity length adjustment element is a piezoelectric ceramic 12, one end of which is fixed and the other end is connected to a cavity mirror of the laser resonant cavity 3. By changing the voltage applied to the piezoelectric ceramic 12, the piezoelectric ceramic 12 is extended or retracted along the optical path, thereby causing the cavity mirror connected to the piezoelectric ceramic 12 to move along the optical path, thereby changing the cavity length of the laser resonant cavity 3.

[0044] In another exemplary embodiment of this application, the etalon 10 locking feedback system includes an etalon 10, a galvanometer motor 11, an optical beam splitter 13, a photodetector 14, and a servo controller 15.

[0045] The etalon 10 is fixed on the rotating shaft of the galvanometer motor 11. The galvanometer motor 11 drives the etalon 10 to rotate by rotating the rotating shaft, thereby changing the center wavelength of the transmission peak of the etalon 10.

[0046] The optical beam splitter 13 is disposed on the output optical path of the laser resonant cavity 3. The optical beam splitter 13 is used to split the laser beam output by the laser resonant cavity 3 into two beams: a probe beam and a main output beam. The probe beam is incident on the photodetector 14, and the main output beam serves as the main laser output of the single-frequency continuous wave tunable alexandrite laser.

[0047] The photodetector 14 is used to convert the optical signal of the received detection beam into an electrical signal and output the electrical signal to the servo controller 15.

[0048] The servo controller 15 is used to generate a feedback control signal based on the received electrical signal and output the feedback control signal to the galvanometer motor 11 to drive the galvanometer motor 11 to rotate and drive the etalon 10 to rotate, thereby locking the transmission peak of the etalon 10 at the oscillation frequency of the laser resonant cavity 3.

[0049] The optical beam splitter 13 reflects 0.5% of the light beam to the photodetector 14 as the detection beam, and transmits 99.5% of the light beam as the main output beam.

[0050] The photodetector 14 receives the detection beam using an external cavity detection method.

[0051] The servo controller 15 includes a mixer circuit, a low-pass filter circuit, and a PI control circuit. The mixer circuit, the low-pass filter circuit, and the PI control circuit are used to extract the deviation signal between the transmission peak of the etalon 10 and the oscillation frequency of the laser resonant cavity 3 and generate a corresponding control signal.

[0052] In another exemplary embodiment of this application, the doping atomic fraction of the first laser crystal 4 and the second laser crystal 5 is 0.13% or 0.2%; the first laser crystal 4 and the second laser crystal 5 are each independently a structure with a single-end small-angle wedge cut and both ends coated with anti-reflection films for pump light wavelength and laser wavelength, or a structure with both ends cut with Brewster angle.

[0053] The wedge angle of the single-end small-angle wedge cut is 0.5°. The single-end small-angle wedge cut is used to suppress the etalon effect on the end faces of the first laser crystal 4 and the second laser crystal 5. The anti-reflection coating on both ends is used to reduce the reflection loss of pump light and laser at the end faces of the crystal. The Brewster angle of the double-end Brewster angle cut is 60.14°. The double-end Brewster angle cut is used to make the laser incident on the end face of the crystal at a Brewster angle to reduce reflection loss, while avoiding the etalon effect of the crystal.

[0054] The distances between the first end face 4-1 and the second end face 4-2 of the first laser crystal 4 and the second pump coupling lens and the sixth pump coupling lens are both 50 mm; the distances between the first end face 5-1 and the second end face 5-2 of the second laser crystal 5 and the fifth pump coupling lens and the third pump coupling lens are both 50 mm.

[0055] Compared with the prior art, the solution provided in this embodiment has at least the following advantages: 1. A dual-crystal structure with symmetrical pumping at both ends is adopted. The pump light is split and polarized by a half-wave plate and a polarizing beam splitter, so that the pump light incident on the crystal has the same power and polarization direction. This allows the pump light to be incident symmetrically from both ends of the emerald crystal, which is beneficial to improving the absorption and utilization efficiency of the pump and improving the thermal distribution of the crystal.

[0056] 2. By combining the intracavity birefringent filter 9, the etalon 10, and the piezoelectric ceramic 12, coarse tuning of the laser wavelength, selection of the longitudinal mode, fine adjustment of the frequency, and continuous tuning are achieved, resulting in a compact and stable single-frequency continuous-wave tunable alexandrite laser.

[0057] In another exemplary embodiment of this application, a single-frequency continuous-wave tunable alexandrite laser is provided, including a first pump source 1-1 and its coupling system 1 (i.e., the first pump optical path), a second pump source 2-1 and its coupling system 2 (i.e., the second pump optical path), a laser resonator 3, a first laser crystal 4, a second laser crystal 5, a first intracavity lens 6, a second intracavity lens 7, an optical one-way device 8, a birefringent filter 9, an etalon 10, a galvanometer motor 11, a piezoelectric ceramic 12, an optical beam splitter 13, a photodetector 14, and a servo controller 15.

[0058] The first pump source 1-1 and its coupling system 1 are configured such that the pump beam output from the first pump source 1-1 is collimated by the first half-wave plate 1-2 and the first pump coupling lens 1-3, and then split into two beams with mutually perpendicular polarization directions by the first polarization beam splitter 1-4; wherein, the transmitted light of the first polarization beam splitter 1-4 is focused on the first end face 4-1 of the first laser crystal 4 by the second pump coupling lens 1-5, and the reflected light of the first polarization beam splitter 1-4 is focused on the second end face 5-2 of the second laser crystal 5 after passing through the first pump reflector 1-6, the second half-wave plate 1-7, the second pump reflector 1-8, and the third pump coupling lens 1-9 in sequence.

[0059] The second pump source 2-1 and its coupling system 2 are configured such that the pump beam output from the second pump source 2-1 is collimated by the third half-wave plate 2-2 and the fourth pump coupling lens 2-3, and then split into two beams with mutually perpendicular polarization directions by the second polarization beam splitter 2-4; wherein, the transmitted light from the second polarization beam splitter 2-4 is focused on the first end face 5-1 of the second laser crystal 5 by the fifth pump coupling lens 2-5, and the reflected light from the second polarization beam splitter 2-4 is focused on the second end face 4-2 of the first laser crystal 4 after passing through the third pump reflector 2-6, the fourth half-wave plate 2-7, the fourth pump reflector 2-8, and the sixth pump coupling lens 2-9 in sequence.

[0060] The first pump source 1-1 and its coupling system 1, and the second pump source 2-1 and its coupling system 2, respectively, perform polarization adjustment, beam splitting, and focusing on the pump light, so that the pump light is incident from the two end faces of the first laser crystal 4 and the second laser crystal 5 towards each other. Specifically, by adjusting the first half-wave plate 1-2 and the third half-wave plate 2-2, the power of the two pump lights after beam splitting by the polarizing beam splitter is made equal; simultaneously, by adjusting the second half-wave plate 1-7 and the fourth half-wave plate 2-7, the polarization state of the pump light is changed, so that the polarization direction of the pump light incident on the first laser crystal 4 and the second laser crystal 5 satisfies the optimal absorption conditions of the alexandrite crystal. Therefore, the pump beams at both ends of the first laser crystal 4 and the second laser crystal 5 have the same optical power and polarization direction, realizing a dual-crystal structure with symmetrical pumping at both ends.

[0061] The first pump source 1-1 and the second pump source 2-1 are both semiconductor laser diodes, with a center wavelength of 638 nm for their output pump light. The first laser crystal 4 and the second laser crystal 5 are alexandrite crystals. The etalon 10 is a fused silica sheet. The photodetector 14 employs an external cavity detection method.

[0062] In another exemplary embodiment of this application, a single-frequency continuous-wave tunable alexandrite laser is provided, including a first pump source 1-1 and its coupling system 1, a second pump source 2-1 and its coupling system 2, a laser resonant cavity 3, a first laser crystal 4, a second laser crystal 5, a first intracavity lens 6, a second intracavity lens 7, an optical one-way device 8, a birefringent filter 9, an etalon 10, a galvanometer motor 11, a piezoelectric ceramic 12, an optical beam splitter 13, a photodetector 14, and a servo controller 15.

[0063] This embodiment employs a dual-crystal structure with symmetrical dual-end pumping. Specifically, the first pump source 1-1 and its coupling system 1, and the second pump source 2-1 and its coupling system 2, respectively, perform polarization adjustment, beam splitting, and focusing on the pump light, so that the pump light is incident from the two end faces of the first laser crystal 4 and the second laser crystal 5, thus forming a dual-end pumping structure. By adjusting the angle of the half-wave plate, the power of the two pump beams after beam splitting by the polarizing beam splitter is made equal; simultaneously, by adjusting the half-wave plate to change the polarization state, the polarization direction of the pump light incident on the first laser crystal 4 and the second laser crystal 5 satisfies the optimal absorption conditions of the alexandrite crystal. Through the above structure, the pump beams at both ends of the first laser crystal 4 and the second laser crystal 5 have the same optical power and polarization direction.

[0064] In this embodiment, a feedback circuit is used to control the position of the etalon 10, so that the transmission peak of the etalon 10 tracks and locks to the laser output frequency. When the laser cavity length changes continuously, the laser output frequency changes, and the feedback system controls the galvanometer motor 11 to adjust the angle of the etalon 10 so that the transmission peak of the etalon 10 matches the laser output frequency.

[0065] The first pump source 1-1 and the second pump source 2-1 are both semiconductor laser diodes, with a center wavelength of 638 nm for their output pump light. The first laser crystal 4 and the second laser crystal 5 are alexandrite crystals. The etalon 10 is a fused silica sheet. The coarse tuning element, the birefringent filter 9, is composed of quartz crystals of a certain thickness and is placed in the optical path at Brewster's angle. The piezoelectric ceramic 12 is fixed together with the resonant cavity mirror; changing the voltage of the piezoelectric ceramic 12 can adjust the cavity length of the laser resonant cavity, achieving continuous tuning of the laser frequency. The photodetector 14 uses an external cavity detection method. The beam splitter separates a small portion of the beam into the photodetector 14, with the remainder serving as the main laser output.

[0066] The servo controller 15 includes a mixer circuit, a low-pass filter circuit, and a PI control circuit, which are used to extract the deviation signal between the transmission peak of the etalon 10 and the laser oscillation frequency and generate a corresponding control signal.

[0067] The standard etalon 10 is fixed on the rotating shaft of the galvanometer motor 11. The galvanometer motor 11 controls the angle of the standard etalon 10, thereby locking the transmission peak of the standard etalon 10 at the oscillation frequency of the resonant cavity in real time.

[0068] In summary, this embodiment improves crystal heat distribution and pump utilization efficiency by employing a dual-crystal structure with dual-end symmetrical pumping, thereby enhancing laser output performance. Simultaneously, by combining intracavity etalon 10 locking, a compact, stable, and frequency-tunable single-frequency continuous-wave alexandrite laser is obtained.

[0069] In another exemplary embodiment of this application, such as Figure 1 As shown, a single-frequency continuous-wave tunable alexandrite laser is provided, including a first pump source 1-1 and its coupling system 1, a second pump source 2-1 and its coupling system 2, a laser resonant cavity 3, a first laser crystal 4, a second laser crystal 5, a first intracavity lens 6, a second intracavity lens 7, an optical one-way device 8, a birefringent filter 9, an etalon 10, a galvanometer motor 11, a piezoelectric ceramic 12, an optical beam splitter 13, a photodetector 14, and a servo controller 15.

[0070] The first pump source 1-1 and its coupling system 1 are configured such that the pump beam output from the first pump source 1-1 is collimated by the first half-wave plate 1-2 and the first pump coupling lens 1-3, and then split into two beams with mutually perpendicular polarization directions by the first polarization beam splitter 1-4; wherein, the transmitted light of the first polarization beam splitter 1-4 is focused on the first end face 4-1 of the first laser crystal 4 by the second pump coupling lens 1-5, and the reflected light of the first polarization beam splitter 1-4 is focused on the second end face 5-2 of the second laser crystal 5 after passing through the first pump reflector 1-6, the second half-wave plate 1-7, the second pump reflector 1-8, and the third pump coupling lens 1-9 in sequence. Similarly, the second pump source 2-1 and its coupling system 2 are configured such that the pump beam output from the second pump source 2-1 is collimated by the third half-wave plate 2-2 and the fourth pump coupling lens 2-3, and then split into two beams with mutually perpendicular polarization directions by the second polarization beam splitter 2-4; wherein, the transmitted light of the second polarization beam splitter 2-4 is focused on the first end face 5-1 of the second laser crystal 5 by the fifth pump coupling lens 2-5, and the reflected light of the second polarization beam splitter 2-4 is focused on the second end face 4-2 of the first laser crystal 4 after passing through the fourth pump reflector 2-8, the fourth half-wave plate 2-7, the fifth pump reflector, and the sixth pump coupling lens 2-9 in sequence. The pump light transmitted through the first polarizing beam splitter 1-4 and the second polarizing beam splitter 2-4 has a polarization direction parallel to the b-axis of the first laser crystal 4 and the second laser crystal 5, respectively. The pump light reflected by the first polarizing beam splitter 1-4 and the second polarizing beam splitter 2-4 has a polarization direction perpendicular to the b-axis of the first laser crystal 4 and the second laser crystal 5, respectively. By adjusting the second half-wave plate 1-7 and the fourth half-wave plate 2-7, the polarization direction of the pump light is made parallel to the b-axis of the first laser crystal 4 and the second laser crystal 5, respectively, thereby maximizing the absorption efficiency of the laser crystal. By adjusting the first half-wave plate 1-2 and the third half-wave plate 2-2, the power of the transmitted beam and the reflected beam of the first polarizing beam splitter 1-4 and the second polarizing beam splitter 2-4 are made equal, respectively. Moreover, the first pump source 1-1 and the second pump source 2-1 use the same type of semiconductor diode laser and have the same output power. In this way, the pump beam focused by the pump coupling system at the first end face 5-1 and the second end face 5-2 of the first laser crystal 4 and the second laser crystal 5 has the same optical power and polarization direction, thereby realizing a dual-crystal structure laser with double-ended symmetrical pumping.

[0071] The laser resonant cavity 3 is a ring resonant cavity composed of a first cavity mirror 3-1, a second cavity mirror 3-2, a third cavity mirror 3-3, a fourth cavity mirror 3-4, a fifth cavity mirror 3-5, and a sixth cavity mirror 3-6. A first laser crystal 4 is positioned between the first cavity mirror 3-1 and the second cavity mirror 3-2, and a second laser crystal 5 is positioned between the first cavity mirror 3-1 and the third cavity mirror 3-3. The distances between the first end face 4-1 and the second end face 4-2 of the first laser crystal 4 and the second pump coupling lens 1-5 and the sixth pump coupling lens 2-9, respectively, are both 50 mm. Similarly, the distances between the first end face 5-1 and the second end face 5-2 of the second laser crystal 5 and the fifth pump coupling lens 2-5 and the third pump coupling lens 1-9, respectively, are also both 50 mm. mm; In a clockwise direction, the laser generated by the pumping of the laser crystal is reflected by the second cavity mirror 3-2. The first cavity lens 6 and the fifth cavity mirror 3-5 are arranged sequentially on the reflected light path of the second cavity mirror 3-2. The optical one-way device 8 and the sixth cavity mirror 3-6 are arranged sequentially on the reflected light path of the fifth cavity mirror 3-5. The transmitted light of the sixth cavity mirror 3-6 serves as the output beam of the laser resonant cavity 3. The birefringent filter 9 and the fourth cavity mirror 3-4 are arranged sequentially on the reflected light path of the sixth cavity mirror 3-6. The etalon 10, the second cavity lens 7 and the third cavity mirror 3-3 are arranged sequentially on the reflected light path of the fourth cavity mirror 3-4. The reflected light of the third cavity mirror 3-3 passes through the second laser crystal 5 and is reflected by the first cavity mirror 3-1. The reflected light of the first cavity mirror 3-1 passes through the first laser crystal 4 and is incident on the second cavity mirror 3-2, forming a ring light path.

[0072] The first cavity mirror 3-1, the second cavity mirror 3-2, the third cavity mirror 3-3, the fourth cavity mirror 3-4, the fifth cavity mirror 3-5, and the sixth cavity mirror 3-6 are all plane mirrors with an incident angle of 45°. Among them, the first cavity mirror 3-1, the second cavity mirror 3-2, and the third cavity mirror 3-3 are coated with a high transmittance coating for 638 nm pump light (T>95%) and a high reflectance coating for 700-850 nm laser light (R>99.9%). The fourth cavity mirror 3-4 and the fifth cavity mirror 3-5 are coated with a high reflectance coating for 700-850 nm laser light (R>99.9%). The sixth cavity mirror 3-6 is coated with a partial transmission coating for 700-850 nm laser light (T = 1%).

[0073] The first laser crystal 4 and the second laser crystal 5 are doped with 0.13% or 0.2% of atoms, and are cut at a small angle (0.5°) on one end (4-1, 5-1 or 4-2, 5-2) and coated with antireflective films of 638 nm and 700-850 nm on both ends, or cut at Brewster angle (60.14°) on both ends.

[0074] The optical one-way device 8 consists of a natural optical rotation compensation plate 8-1 and an externally applied permanent magnetic field terbium gallium garnet crystal 8-2. The birefringent filter 9 is made of three quartz crystal materials with parallel optical axes and a thickness ratio of 1:2:4. Both the optical one-way device 8 and the birefringent filter 9 are placed at Brewster angles. The etalon 10 is a fused silica sheet with a thickness of 0.5 mm and a surface coated with 700-850 nm reflectivity of 20%, and is bonded to the rotation shaft of the galvanometer motor 11 for adjusting and feedback control of the etalon 10 angle. The fourth cavity mirror 3-4 is bonded to the piezoelectric ceramic 12 and is used to adjust the cavity length of the laser resonant cavity 3.

[0075] The laser beam output from the laser resonant cavity 3 is reflected by the optical beam splitter 13, with approximately 0.5% of the beam incident on the photodetector 14; approximately 99.5% of the beam transmitted by the optical beam splitter 13 serves as the main laser output; the photodetector 14 converts the incident light signal into an electrical signal and inputs it to the servo controller 15, and the control signal generated by the servo controller 15 is input to the galvanometer motor 11, thereby controlling the angle of the etalon 10 by controlling the rotation of the galvanometer motor 11 shaft, thus achieving real-time locking between the etalon 10 and the oscillation mode within the laser resonant cavity 3.

[0076] After the laser is working normally, the laser frequency is coarsely tuned by the birefringent filter 9, the coarse tuning element, and then finely tuned by rotating the etalon 10, the fine tuning element. Finally, the laser frequency is continuously tuned by scanning the piezoelectric ceramic 12 connected to the cavity mirror to continuously change the cavity length.

[0077] Adjust the birefringent filter 9, the coarse tuning element, to bring the laser output wavelength to approximately 766.5 nm. Rotate the etalon 10 to bring the laser output wavelength to approximately 766.500 nm, and lock the transmission peak of the etalon 10 at the laser oscillation frequency in real time. Scan the length of the piezoelectric ceramic 12 to obtain... Figure 2 The results of the continuous tuning experiment are shown. The alexandrite laser achieved continuous frequency tuning through the combined action of the coarse tuning element (birefringent filter 9), the fine tuning element (etalon 10), and the precision tuning element (piezoelectric ceramic 12).

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A single-frequency continuous-wave tunable alexandrite laser, characterized in that, include: The system comprises a first pump optical path, a second pump optical path, a first laser crystal, a second laser crystal, and a laser resonant cavity; Both the first and second laser crystals are emerald green crystals, symmetrically arranged within the laser resonant cavity; The first pump optical path includes a first pump source, a first polarization beam splitter, a first focusing group, a second focusing group, a fifth focusing group, and a first beam steering group; the pump light output from the first pump source is collimated by the fifth focusing group and then incident on the first polarization beam splitter, which splits it into a first transmitted light and a first reflected light. The first transmitted light is incident on the first end face of the first laser crystal through the first focusing group, and the first reflected light is redirected by the first beam steering group and then incident on the second end face of the second laser crystal through the second focusing group. The second pump optical path includes a second pump source, a second polarization beam splitter, a third focusing group, a fourth focusing group, a sixth focusing group, and a second beam steering group. The pump light output from the second pump source is collimated by the sixth focusing group and then incident on the second polarization beam splitter. The second polarization beam splitter splits the light into a second transmitted light and a second reflected light. The second transmitted light is incident on the first end face of the second laser crystal through the third focusing group. The second reflected light is redirected by the second beam steering group and then incident on the second end face of the first laser crystal through the fourth focusing group. The first pump optical path has a first polarization adjustment element before the first polarization beam splitter, and the second pump optical path has a second polarization adjustment element before the second polarization beam splitter. By adjusting the first polarization adjustment element and the second polarization adjustment element, the power of the transmitted light and the reflected light after being split by each polarization beam splitter is equal. The first beam steering group is provided with a third polarization adjustment element, and the second beam steering group is provided with a fourth polarization adjustment element. The third polarization adjustment element is used to adjust the polarization direction of the first reflected light to be consistent with the polarization direction of the first transmitted light, and the fourth polarization adjustment element is used to adjust the polarization direction of the second reflected light to be consistent with the polarization direction of the second transmitted light. The adjusted polarization directions both satisfy the optimal absorption polarization direction of the emerald crystal, so that the pump light incident on all end faces of the two laser crystals has equal power and consistent polarization state, forming a dual-crystal gain structure with double-ended symmetrical pumping. The laser resonant cavity is equipped with an etalon locking feedback system and a cavity length adjustment element. The etalon locking feedback system locks the transmission peak of the etalon to the oscillation frequency of the laser resonant cavity, and the cavity length adjustment element achieves continuous tuning of the laser frequency by changing the cavity length of the laser resonant cavity.

2. The single-frequency continuous-wave tunable alexandrite laser according to claim 1, characterized in that, The first focusing group, the second focusing group, the third focusing group, and the fourth focusing group are all pump-coupled lenses; the first pump optical path is further provided with a fifth focusing group before the first polarization beam splitter, which is used to collimate the pump light output from the first pump source and then incident it onto the first polarization beam splitter; the second pump optical path is further provided with a sixth focusing group before the second polarization beam splitter, which is used to collimate the pump light output from the second pump source and then incident it onto the second polarization beam splitter; The first polarization adjustment element, the second polarization adjustment element, the third polarization adjustment element, and the fourth polarization adjustment element are all half-wave plates; The pump light output from the first pump source passes sequentially through the first polarization adjustment element, the fifth focusing group, and the first polarization beam splitter. The transmitted light from the first polarization beam splitter is incident on the first end face of the first laser crystal through the first focusing group. The reflected light from the first polarization beam splitter passes sequentially through the first mirror in the first beam steering group, the third polarization adjustment element, the second mirror, and the second focusing group before being incident on the second end face of the second laser crystal. The pump light output from the second pump source passes sequentially through the second polarization adjustment element, the sixth focusing group, and the second polarization beam splitter. The transmitted light from the second polarization beam splitter is incident on the first end face of the second laser crystal through the third focusing group. The reflected light from the second polarization beam splitter passes sequentially through the third mirror in the second beam steering group, the fourth polarization adjustment element, the fourth mirror, and the fourth focusing group before being incident on the second end face of the first laser crystal. The first polarization adjustment element is used to adjust the polarization direction of the output beam of the first pump source to change the power ratio of the transmitted light to the reflected light of the first polarization beam splitter; the second polarization adjustment element is used to adjust the polarization direction of the output beam of the second pump source to change the power ratio of the transmitted light to the reflected light of the second polarization beam splitter.

3. The single-frequency continuous-wave tunable alexandrite laser according to claim 1, characterized in that, The laser resonant cavity is a ring resonant cavity; the laser resonant cavity includes a first cavity mirror, a second cavity mirror, a third cavity mirror, a fourth cavity mirror, a fifth cavity mirror, and a sixth cavity mirror; The first laser crystal is disposed in the optical path between the first cavity mirror and the second cavity mirror, and the second laser crystal is disposed in the optical path between the first cavity mirror and the third cavity mirror; In a clockwise direction, the laser light generated by the stimulated emission of the first laser crystal and the second laser crystal is reflected by the second cavity mirror and then passes sequentially through the first cavity lens and the fifth cavity mirror. The fifth cavity mirror reflects the incident light to the optical one-way device, and after passing through the optical one-way device, it is incident to the sixth cavity mirror. The sixth cavity mirror transmits a portion of the incident light as the output beam of the laser resonant cavity, and reflects the other portion to the wavelength tuning element. After being selected by the wavelength tuning element, the incident light is incident on the fourth cavity mirror, which reflects the incident light to the etalon. After being selected by the etalon, the incident light is incident on the second intracavity lens, and then on the third cavity mirror. The third cavity mirror reflects the incident light and passes it through the second laser crystal before it is incident on the first cavity mirror. The first cavity mirror reflects the incident light and passes it through the first laser crystal before it is incident on the second cavity mirror, forming a ring optical path.

4. The single-frequency continuous-wave tunable alexandrite laser according to claim 3, characterized in that, The first cavity mirror, the second cavity mirror, the third cavity mirror, the fourth cavity mirror, the fifth cavity mirror, and the sixth cavity mirror are all planar reflecting mirrors that are tilted at 45° relative to the incident light; The first cavity mirror, the second cavity mirror, and the third cavity mirror are all used to transmit pump light into the laser resonant cavity and to reflect and oscillate the laser within the cavity. Each cavity mirror is coated with a film layer that is highly transparent to the pump light wavelength and highly reflective to the laser wavelength. Both the fourth and fifth cavity mirrors are used to reflect and oscillate the laser within the cavity, and each cavity mirror is coated with a film layer that is highly reflective to the laser wavelength. The sixth cavity mirror is used to output part of the laser from the cavity and to reflect part of the laser back into the cavity to continue oscillating. The sixth cavity mirror is coated with a film layer that transmits a portion of the laser wavelength.

5. The single-frequency continuous-wave tunable alexandrite laser according to claim 4, characterized in that, The first cavity mirror, the second cavity mirror, and the third cavity mirror are all coated with a film layer that has a transmittance of more than 95% for 638 nm pump light and a reflectance of more than 99.9% for 700 nm to 850 nm laser light. Both the fourth and fifth cavity mirrors are coated with a film layer that has a reflectivity of greater than 99.9% for lasers in the 700 nm to 850 nm range. The sixth cavity mirror is coated with a film that has a transmittance of 1% for lasers in the range of 700 nm to 850 nm.

6. The single-frequency continuous-wave tunable alexandrite laser according to claim 3, characterized in that, Both the first pump source and the second pump source are semiconductor laser diodes. The center wavelength of the pump light output by the first pump source and the second pump source is 638 nm, and the first pump source and the second pump source have the same output power. The optical one-way device is disposed in the optical path between the fifth cavity mirror and the sixth cavity mirror. The optical one-way device is used to force the laser in the laser resonant cavity to run in a single direction to prevent the spatial hole burning effect. The optical one-way device is composed of a natural optical rotation compensation plate and a terbium gallium garnet crystal with an external permanent magnetic field. The optical one-way device is placed in the optical path at Brewster angle. The wavelength tuning element is disposed in the optical path between the sixth cavity mirror and the fourth cavity mirror. The wavelength tuning element is used to perform coarse wavelength tuning on the laser in the laser resonant cavity. The wavelength tuning element is a birefringent filter. The birefringent filter is placed in the optical path at Brewster angle. The birefringent filter is made of three pieces of quartz crystal material with parallel optical axes and a thickness ratio of 1:2:

4.

7. The single-frequency continuous-wave tunable alexandrite laser according to claim 3, characterized in that, The etalon is disposed in the optical path between the fourth cavity mirror and the second intracavity lens. The etalon is used to perform longitudinal mode selection on the laser in the laser resonant cavity to suppress longitudinal mode oscillations other than the transmission peak center frequency. The etalon is a fused silica sheet with a thickness of 0.5 mm, and the surface of the etalon is coated with a film layer with a reflectivity of 20% for lasers in the range of 700 nm to 850 nm.

8. The single-frequency continuous-wave tunable alexandrite laser according to claim 3, characterized in that, The cavity length adjustment element is a piezoelectric ceramic. One end of the piezoelectric ceramic is fixed, and the other end of the piezoelectric ceramic is connected to a cavity mirror of the laser resonant cavity. By changing the voltage applied to the piezoelectric ceramic, the piezoelectric ceramic is extended or retracted along the optical path, thereby causing the cavity mirror connected to the piezoelectric ceramic to move along the optical path, thus changing the cavity length of the laser resonant cavity.

9. The single-frequency continuous-wave tunable alexandrite laser according to claim 1, characterized in that, The etalon locking feedback system includes an etalon, a galvanometer motor, an optical beam splitter, a photodetector, and a servo controller; The standard is fixed on the rotating shaft of the galvanometer motor. The galvanometer motor drives the standard to rotate by rotating the rotating shaft, thereby changing the center wavelength of the transmission peak of the standard. The optical beam splitter is disposed on the output optical path of the laser resonant cavity. The optical beam splitter is used to split the laser beam output by the laser resonant cavity into two beams: a probe beam and a main output beam. The probe beam is incident on the photodetector, and the main output beam serves as the main laser output of the single-frequency continuous wave tunable alexandrite laser. The photodetector is used to convert the optical signal of the received probe beam into an electrical signal, and output the electrical signal to the servo controller; The servo controller is used to generate a feedback control signal based on the received electrical signal, and output the feedback control signal to the galvanometer motor to drive the galvanometer motor to rotate and drive the etalon to rotate, thereby locking the transmission peak of the etalon at the oscillation frequency of the laser resonant cavity. The optical beam splitter reflects 0.5% of the light beam to the photodetector as the detection beam, and the optical beam splitter transmits 99.5% of the light beam as the main output beam; The photodetector receives the detection beam using an external cavity detection method; The servo controller includes a mixer circuit, a low-pass filter circuit, and a PI control circuit. The mixer circuit, the low-pass filter circuit, and the PI control circuit are used to extract the deviation signal between the transmission peak of the etalon and the oscillation frequency of the laser resonant cavity and generate a corresponding control signal.

10. The single-frequency continuous-wave tunable alexandrite laser according to claim 1, characterized in that, The first laser crystal and the second laser crystal have a doping atomic fraction of 0.13% or 0.2%; the first laser crystal and the second laser crystal are each independently a structure with a small-angle wedge cut at one end and anti-reflection coatings for pump wavelength and laser wavelength deposited at both ends, or a structure with Brewster angle cut at both ends; The single-end small-angle wedge cut has a wedge angle of 0.5°. The single-end small-angle wedge cut is used to suppress the etalon effect on the end faces of the first laser crystal and the second laser crystal. The anti-reflection coating deposited on both ends is used to reduce the reflection loss of pump light and laser at the end face of the crystal. The double-end Brewster angle cut has a Brewster angle of 60.14°. The double-end Brewster angle cut is used to make the laser incident on the end face of the crystal at a Brewster angle to reduce reflection loss. The distances between the first and second end faces of the first laser crystal and the first and fourth focusing groups are both 50 mm; the distances between the first and second end faces of the second laser crystal and the third and second focusing groups are both 50 mm.

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