Based on Tm 3+ Three-wavelength mid-infrared solid-state lasers with doped crystals and their operating methods

Abstract

The application belongs to the technical field of all-solid-state laser, and particularly relates to a three-wavelength mid-infrared solid laser based on Tm 3+ The three-wavelength mid-infrared solid laser has a continuous operation mode and a pulse operation mode, and comprises a pump laser, a beam collimation and focusing system, a resonant cavity and a dichroic mirror arranged along an optical path; when the three-wavelength mid-infrared solid laser is in the pulse operation mode, an electro-optic Q-switching system is arranged in the resonant cavity. The three-wavelength mid-infrared solid laser based on Tm 3+ ions 3 F4→ 3 H6、 3 H4→ 3 H5 and 3 H5→ 3 F4 three energy levels, and the energy level regulation means of cascade laser oscillation at about 1.9 microns, about 2.3 microns and about 3.8 microns can effectively improve quantum efficiency, reduce thermal effect of the laser crystal, and realize efficient operation of three-wavelength mid-infrared continuous and pulse lasers. The application can simultaneously and sensitively monitor multiple gases by using one laser, has the advantages of compact structure and low price, and can greatly promote the development of gas detection technology.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state laser technology, specifically relating to a Tm-based... 3+ Three-wavelength mid-infrared solid-state lasers with doped crystals and their operating methods. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Mid-infrared lasers have significant applications in environmental monitoring, optoelectronic countermeasures, medical diagnosis, and scientific research, and have attracted widespread attention in recent years. In gas detection, lasers in the 1.5-4 μm band cover the absorption spectra of various gas molecules, such as acetylene (~1.5 μm), carbon dioxide (~1.9 μm), carbon monoxide (~2.3 μm), and hydrogen bromide (~3.8 μm), enabling highly sensitive trace gas detection.

[0004] Tunable semiconductor laser absorption spectroscopy is a crucial method for trace gas monitoring and analysis. It achieves rapid wavelength tuning by altering the driving current of the semiconductor laser, utilizing the absorption of the analyte gas at a specific laser wavelength to detect gas composition, content, and volume. However, this method has a limited current adjustment range, making it difficult to cover the characteristic absorption peaks of multiple gas molecules. Therefore, a single laser often can only measure one gas, hindering the monitoring of multiple gases. Rare earth ions, with their rich energy level structure, generate lasers of different wavelengths through transitions between different energy levels. Furthermore, mature commercial semiconductor lasers can directly pump rare earth ion-doped gain media, making it a powerful tool for achieving efficient operation of mid-infrared multi-wavelength lasers to detect multiple gases. Among these, Tm... 3+ Ions can generate lasers in the ~1.5μm, ~1.9μm, ~2.3μm, and ~3.8μm wavelength bands, respectively corresponding to... 3 H4→ 3 F4 3 F4→ 3 H6 3 H4→ 3 H5 and 3 H5→ 3 F4 level transition. However, current research largely utilizes Tm. 3+ Ion-doped tellurate glass, fluoride optical fibers, and telluride microspheres were used to achieve dual-wavelength laser oscillations at ~1.5μm and ~1.9μm, and ~1.9μm and ~2.3μm, as well as tri-wavelength oscillations at ~1.5μm, ~1.9μm, and ~2.3μm, utilizing Tm 3+While doped crystals have enabled dual-wavelength laser output at ~1.5μm and ~2.3μm, and ~2μm and ~2.3μm, and ~3.8μm laser output has been achieved by pumping an optical superlattice crystal with a ~1.9μm laser using nonlinear frequency conversion, there are currently no reports on direct oscillation output of three mid-infrared laser wavelengths at ~1.9μm, ~2.3μm, and ~3.8μm. Furthermore, the high brittleness and poor thermal stability of tellurate glass fibers, and the limited tensile strength and low melting temperature of fluoride fibers, hinder further increases in the output power of mid-infrared multi-wavelength lasers. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a Tm-based... 3+ A three-wavelength mid-infrared solid-state laser with doped crystals and its operating method. This invention uses a commercial semiconductor laser to pump a Tm laser, which has advantages such as weak nonlinearity, high thermal conductivity, and high laser damage threshold. 3+ By optimizing parameters such as the resonant cavity structure, the transmittance of the output mirror to various wavelengths, and the crystal doping concentration, a high-power, multi-wavelength mid-infrared solid-state laser output can be obtained using a doped crystal. This invention can replace traditional gas detection technologies, not only meeting the requirement of simultaneously and sensitively monitoring multiple gases with a single laser, but also offering advantages such as compact structure and low cost, thus playing a significant role in advancing the field of gas detection.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] Firstly, this invention provides a Tm-based 3+ A three-wavelength mid-infrared solid-state laser with doped crystal, comprising a pump laser, a beam collimation and focusing system, a resonant cavity, and a dichroic mirror arranged along the optical path; the resonant cavity comprising an input mirror, a Tm... 3+ Doped crystals, dichroic mirrors, ~1.9μm single-wavelength output mirrors and ~2.3μm and ~3.8μm dual-wavelength output mirrors.

[0008] Preferably, the dichroic mirror is disposed at Tm 3+ The doped crystal is placed between the ~2.3μm and ~3.8μm dual-wavelength output mirrors, with the dichroic mirror at an angle of 10-30° to the optical path, and the ~1.9μm single-wavelength output mirror is placed on one side of the dichroic mirror.

[0009] Preferably, an electro-optic Q-switching system is provided in the resonant cavity, and the electro-optic Q-switching system is located between the dichroic mirror and the ~1.9μm single-wavelength output mirror. The electro-optic Q-switching system includes a polarizer, an electro-optic switch and a quarter-wave plate arranged sequentially along the optical path.

[0010] The present invention is based on Tm 3+ The doped crystal three-wavelength mid-infrared solid-state laser has two operating modes: continuous operation and pulsed operation. When the three-wavelength mid-infrared solid-state laser is in continuous operation mode, the pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then enters the Tm laser through the input mirror. 3+ A doped crystal first achieves a ~1.9μm laser output within the resonant cavity, then forms a three-wavelength cascaded laser oscillation. The resulting continuous laser outputs through the ~1.9μm single-wavelength output mirror and the ~2.3μm and ~3.8μm dual-wavelength output mirrors, respectively. When the three-wavelength mid-infrared solid-state laser is in pulsed operating mode, the pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then incident on the Tm laser through the input mirror. 3+ The doped crystal and the electro-optic Q-switching system modulate the resonant cavity loss to first achieve a ~1.9μm single-wavelength pulsed laser output, and then form a three-wavelength laser cascade oscillation. The generated pulsed laser is output through the ~1.9μm single-wavelength output mirror and the ~2.3μm and ~3.8μm dual-wavelength output mirrors, respectively.

[0011] Preferably, the pump laser comprises a semiconductor laser or a Ti:sapphire laser, the pump laser operating at a wavelength of 770-800 nm and a maximum output power of 50 W. This wavelength is located in the Tm range. 3+ ion 3 H6→ 3 The absorption peak of H4 is observed, and commercial semiconductor lasers at this wavelength are low-cost, have a flexible and compact structure, and are highly stable. Furthermore, temperature control using a semiconductor cooler (TEC) avoids drift of the pump laser's center wavelength.

[0012] More preferably, the pump laser is equipped with a semiconductor cooler for temperature control.

[0013] The beam collimation and focusing system is used to shape the pump light so that the pump spot and the laser oscillation spot achieve mode matching.

[0014] Preferably, the Tm 3+ Tm in doped crystals 3+ The doping concentration is 1.5-3 at.%, and the Tm 3+ Doped crystals include Tm 3+ Fluoride-doped crystals or Tm 3+ Doped sesquioxide crystals. Due to 3 H5 and 3 The F4 has a small band gap between its two energy levels, making it prone to nonradiative relaxation processes. Matrix materials with lower phonon energies are beneficial for reducing nonradiative transition processes.

[0015] The Tm provided by this invention 3+ Three-wavelength mid-infrared solid-state laser with doped crystal, Tm 3+ A simplified diagram of ion energy levels is shown below. Figure 1 As shown. The process involving the cascaded oscillation of three wavelength lasers includes... 3 H6→ 3 H4 ground-state absorption process (GSA) 3 H4→ 3 F4 3 F4→ 3 H6 3 H4→ 3 H5 3 H5→ 3 F4 radiative transition process, 3 H4+ 3 H6→ 3 F4+ 3 F4 cross-relaxation (CR) process and energy upconversion 3 F4+ 3 F4→ 3 H4+ 3 H6 (ETU) process.

[0016] When the ground state 3 Particles at the H6 energy level transition to the ground state through absorption. 3 At the H4 energy level, because the ~1.9μm wavelength laser has a higher gain and a lower oscillation threshold compared to other wavelengths, the particle number will increase from... 3 The F4 energy level transitions to 3 The H6 energy level, i.e., the ~1.9 μm laser, will preferentially oscillate. This oscillation occurs as the pump power increases and the ~1.9 μm laser energy level... 3 As the number of particles in the F4 energy level is continuously depleted, it will produce... 3 H4→ 3 H5 and 3 H5→ 3 The energy level transitions of F4, at ~2.3 μm and ~3.8 μm, enable laser output, which leads to a large accumulation of particles in the energy level. 3 F4 energy level, and 3 The F4 energy level corresponds exactly to the upper energy level of a laser at approximately 1.9 μm. 3 F4→ 3 The H6 energy level transition will release a large amount of... 3 The number of particles in the F4 energy level and the oscillation efficiency of the ~1.9μm laser are further improved. This cycle will greatly promote the efficient output of the three-wavelength laser.

[0017] from Figure 1 It can be seen that 3 H6→ 3 Under H4 pump light excitation, adjacent Tm3+ There are ions 3 H4+ 3 H6→ 3 F4+ 3 F4 cross-relaxation process, and because 3 H4 level lifetime τ4 and CR rate constant W CR Closely related, that is:

[0018]

[0019]

[0020] Where τ0 is the intrinsic lifetime, C CR It is a concentration-independent CR parameter, N Tm This represents the particle number density. Therefore, the higher the ion doping concentration, the more pronounced the cross-relaxation process. 3 The shorter the lifetime of the H4 level, the better. 3 H6→ 3 Under H4 pumping mode, the doping concentration is too high to achieve three-wavelength cascaded oscillating laser operation.

[0021] Furthermore, Tm 3+ The rate equation for a doped laser in continuous operation mode is as follows:

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] Wherein, N1-N4 are respectively 3 H6 3 F4 3 H5 3 The particle number density at the H4 energy level, R p1 yes 3 H6→ 3 H4 ground-state absorption pump rate, τ i Φ represents the lifetime of the i-th energy level, Φ is the photon number density in the laser resonant cavity, τ is the photon lifetime in the cavity, and β is the photon lifetime. ij k represents the fluorescence branching ratio. CRK represents the cross-relaxation coefficient. ETU W is the energy upconversion coefficient. NRij For non-radiative transition probability, σ 1.9 , σ 2.3 and σ 3.8 These represent the stimulated absorption and emission cross sections of the gain medium at 1.9 μm, 2.3 μm, and 3.8 μm, respectively. Based on the rate equation, the values ​​at Tm can be simulated. 3+ The variation of particle number density at each energy level with time under different doping concentrations is theoretically obtained as Tm. 3+ Optimal doping concentration. In this invention, Tm... 3+ The optimal doping concentration range is 1.5-3 at.%, to reduce the cross-relaxation process and avoid... 3 H4 level fluorescence quenching.

[0030] More preferably, the Tm 3+ Fluoride-doped crystals include Tm:YLF or Tm:LLF, wherein Tm 3+ Doped sesquioxide crystals include Tm:CaF2 or Tm:Lu2O3. The phonon energies of Tm:YLF, Tm:LLF, Tm:CaF2, and Tm:Lu2O3 are 446 cm⁻¹, respectively. -1 400cm -1 350cm -1 And 430cm -1 .

[0031] Preferably, the dichroic mirror is made of CaF2 or ZnSe material and is coated with antireflective coatings for laser wavelengths of ~2.3μm and ~3.8μm with transmittance >99.5% and high reflective coatings for laser wavelengths of ~1.9μm with reflectance >99.8%.

[0032] Preferably, the ~1.9μm single-wavelength output mirror is a flat mirror made of CaF2 or ZnSe material, and is coated with a ~1.9μm three-wavelength laser partial transmission film with T = 5%-10%.

[0033] Preferably, the ~2.3μm and ~3.8μm dual-wavelength output mirror is a flat mirror made of CaF2 or ZnSe material, and is coated with a ~2.3μm and ~3.8μm dual-wavelength laser partial transmission film, T = 1%-5%.

[0034] Preferably, the dichroic mirror is made of CaF2 or ZnSe matrix crystal material, coated with a high-reflectivity film for ~2.3μm wavelength laser with a reflectivity >99.8% and a high-transmittance film for ~3.8μm wavelength laser with a transmittance >99.5%, and is placed at a 45° angle with the ~2.3μm and ~3.8μm dual-wavelength output mirror.

[0035] Preferably, the polarizer has high transmittance for p-polarized laser and high reflectivity for s-polarized laser.

[0036] More preferably, the polarizer includes a polarizing beam splitter prism or a YAG sheet placed at Brewster angle.

[0037] Preferably, the quarter-wave plate is coated with an anti-reflection film for a laser wavelength of ~1.9 μm, exhibiting a transmittance of over 99.5% for a laser wavelength of ~1.9 μm. The quarter-wave plate is disposed between the electro-optic switch and the ~1.9 μm single-wavelength output mirror for modulating the polarization state of the laser.

[0038] Preferably, the electro-optic switch is a boost voltage switch; more preferably, the electro-optic switch is provided with a boost modulation signal by an electro-optic drive power supply. The electro-optic switch, in conjunction with the polarizer and the quarter-wave plate, is used to control intracavity loss and thereby generate pulsed laser.

[0039] Secondly, the present invention provides a Tm-based solution as described in the first aspect. 3+ The operating method of a three-wavelength mid-infrared solid-state laser with doped crystals includes the following steps:

[0040] The pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then enters the Tm through the input mirror. 3+ The doped crystal first achieves ~1.9μm laser output in the resonant cavity, and then forms a three-wavelength laser cascade oscillation. The generated continuous laser is output through the ~1.9μm single-wavelength output mirror and the ~2.3μm and ~3.8μm dual-wavelength output mirrors, respectively.

[0041] Alternatively, the pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then incident on the Tm through the input mirror. 3+ The doped crystal and the electro-optic Q-switching system modulate the resonant cavity loss to first achieve a ~1.9μm single-wavelength pulsed laser output, and then form a three-wavelength laser cascade oscillation. The generated pulsed laser is output through the ~1.9μm single-wavelength output mirror and the ~2.3μm and ~3.8μm dual-wavelength output mirrors, respectively.

[0042] Preferably, the electro-optic Q-switching system modulates the resonant cavity loss by the following steps: rotating the quarter-wave plate until it no longer emits light, turning on the electro-optic drive power supply, which provides a boost modulation signal to the electro-optic switch, adjusting the electro-optic drive voltage, changing the pump power, fine-tuning various components, and selecting the optimal output mirror transmittance to achieve the optimal pulse output of ~1.9μm wavelength laser, and then achieving ~2.3μm and ~3.8μm wavelength laser pulse operation based on the effective energy level control method of cascaded oscillation.

[0043] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0044] 1. Multiwavelength lasers realized using rare-earth ion-doped gain media are often limited to spectral line transitions between a pair of Stark splitter levels with different energy levels, and their development lags behind in the mid-infrared band. This invention is based on Tm 3+ ion 3 F4→ 3 H6 3 H4→ 3 H5 and 3 H5→ 3 Transitions between the three F4 energy levels, utilizing energy level modulation techniques based on cascaded laser oscillations at ~1.9μm, ~2.3μm, and ~3.8μm, effectively improve quantum efficiency, reduce laser crystal thermal effects, and achieve Tm transitions. 3+ The doped crystal all-solid-state multi-wavelength continuous and pulsed laser output opens up a new technical path for the further development of high-power, high-energy mid-infrared multi-wavelength solid-state lasers.

[0045] 2. This invention provides an alternative to traditional gas detection technology, which not only meets the requirement of simultaneously and sensitively monitoring multiple gases using a single laser, but also has the advantages of compact structure and low price, which will greatly promote the development of gas detection technology. Attached Figure Description

[0046] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0047] Figure 1 For Tm 3+ A schematic diagram of the energy levels of an ion;

[0048] Figure 2 The Tm-based embodiment of the present invention provided in Embodiment 1 3+ A schematic diagram of a three-wavelength mid-infrared solid-state laser operating in continuous mode with a doped crystal.

[0049] Figure 3 The Tm-based embodiment provided in Embodiment 2 of the present invention 3+ A schematic diagram of a three-wavelength mid-infrared solid-state laser operating in pulse mode with a doped crystal.

[0050] Explanation of reference numerals in the attached figures

[0051] 101. Pump laser; 201. Beam collimation and focusing system; 301. Input mirror; 302. Dichroic mirror; 303. ~1.9μm single-wavelength output mirror; 304. ~2.3μm and ~3.8μm dual-wavelength output mirror; 305. Tm 3+ Doped crystals, 401, dichroic mirror, 501, polarizer, 502, electro-optic switch, 503, quarter-wave plate. Detailed Implementation

[0052] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0053] Example 1

[0054] like Figure 2 As shown, a method based on Tm 3+ A continuous-mode three-wavelength mid-infrared solid-state laser with doped crystals, comprising a pump laser 101, a beam collimation and focusing system 201, an input mirror 301, and a Tm laser arranged sequentially along the optical path. 3+ Doped crystal 305, dichroic mirror 302, ~1.9μm single-wavelength output mirror 303, ~2.3μm, ~3.8μm dual-wavelength output mirror 304, and dichroic mirror 401; input mirror 301, Tm 3+ The resonant cavity is composed of a doped crystal 305, a dichroic mirror 302, a ~1.9μm single-wavelength output mirror 303, and a ~2.3μm and ~3.8μm dual-wavelength output mirror 304.

[0055] In this embodiment, the pump laser 101 is a commercial semiconductor laser with a maximum output power of 50W and an output center wavelength of 790nm.

[0056] Tm 3+ The doped crystal 305 is a Tm:YLF crystal with a doping concentration of 3 at.% and a size of 3 mm × 3 mm × 10 mm. It has low phonon energy and is easy to grow into a high-quality crystal.

[0057] The input mirror 301 is a flat mirror made of CaF2 material, coated with a pump light anti-reflection film (transmittance >99.5%) and three-wavelength laser high-reflection films (reflectivity >99.8%) for ~1.9μm, ~2.3μm, and ~3.8μm.

[0058] The dichroic mirror 302 is a concave mirror with a curvature of 200mm. It is made of CaF2 material and coated with anti-reflection coatings for lasers with wavelengths of ~2.3μm and ~3.8μm (transmittance >99.5%) and high reflectivity coatings for lasers with wavelengths of ~1.9μm (reflectivity >99.8%). It is placed at an angle of 10-30° with the optical path.

[0059] The ~1.9μm single-wavelength output mirror 303 is a flat mirror made of CaF2 material, coated with a ~1.9μm wavelength laser partial transmission film, T=5%.

[0060] The ~2.3μm and ~3.8μm dual-wavelength output mirror 304 is a flat mirror made of CaF2 material, coated with a laser partial transmission film for ~2.3μm and ~3.8μm wavelengths, with T=1%.

[0061] Dichroic mirror 401 uses a CaF2 matrix crystal, coated with a high-reflectivity film for ~2.3μm wavelength laser (reflectivity >99.8%) and a high-transmittance film for ~3.8μm wavelength laser (transmittance >99.5%), and is placed at a 45° angle with the ~2.3μm and ~3.8μm dual-wavelength output mirrors.

[0062] The pump light emitted by the pump laser 101 passes through the beam collimation and focusing system 201 and then enters Tm through the input mirror 301. 3+ In the doped crystal 305, a ~1.9μm laser output is first achieved in the resonant cavity, and then a three-wavelength laser cascade oscillation is formed. The generated continuous laser is output through a ~1.9μm single-wavelength output mirror 303 and a ~2.3μm and ~3.8μm dual-wavelength output mirror, respectively. A dichroic mirror 401 is used to achieve the ~2.3μm and ~3.8μm dual-wavelength beam splitting.

[0063] The principle of forming a three-wavelength cascaded oscillation within the resonant cavity is as follows:

[0064] When the ground state 3 Particles at the H6 energy level transition to the ground state through absorption. 3 At the H4 energy level, because the ~1.9μm wavelength laser has a higher gain and a lower oscillation threshold compared to other wavelengths, the particle number will increase from... 3 The F4 energy level transitions to 3 The H6 energy level, i.e., the ~1.9 μm laser, will preferentially oscillate. This oscillation occurs as the pump power increases and the ~1.9 μm laser energy level... 3 As the number of particles in the F4 energy level is continuously depleted, it will produce... 3 H4→ 3 H5 and 3 H5→ 3 The energy level transitions of F4, at ~2.3 μm and ~3.8 μm, enable laser output, which leads to a large accumulation of particles in the energy level. 3 F4 energy level, and 3 The F4 energy level corresponds exactly to the upper energy level of a laser at approximately 1.9 μm. 3 F4→ 3 The H6 energy level transition will release a large amount of... 3The number of particles in the F4 energy level and the oscillation efficiency of the ~1.9μm laser are further improved. This cycle will greatly promote the efficient output of the three-wavelength laser.

[0065] from Figure 1 It can be seen that 3 H6→ 3 Under H4 pump light excitation, adjacent Tm 3+ There are ions 3 H4+ 3 H6→ 3 F4+ 3 F4 cross-relaxation process, and because 3 H4 level lifetime τ4 and CR rate constant W CR Closely related, that is:

[0066]

[0067]

[0068] Where τ0 is the intrinsic lifetime, C CR It is a concentration-independent CR parameter, N Tm This represents the particle number density. Therefore, the higher the ion doping concentration, the more pronounced the cross-relaxation process. 3 The shorter the lifetime of the H4 level, the better. 3 H6→ 3 Under H4 pumping mode, the doping concentration is too high to achieve three-wavelength cascaded oscillating laser operation.

[0069] Furthermore, Tm 3+ The rate equation for a doped laser in continuous operation mode is as follows:

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077] Wherein, N1-N4 are respectively 3 H6 3 F4 3 H5 3The particle number density at the H4 energy level, R p1 yes 3 H6→ 3 H4 ground-state absorption pump rate, τ i Φ represents the lifetime of the i-th energy level, Φ is the photon number density in the laser resonant cavity, τ is the photon lifetime in the cavity, and β is the photon lifetime. ij k represents the fluorescence branching ratio. CR K represents the cross-relaxation coefficient. ETU W is the energy upconversion coefficient. NRij For non-radiative transition probability, σ 1.9 , σ 2.3 and σ 3.8 These represent the stimulated absorption and emission cross sections of the gain medium at 1.9 μm, 2.3 μm, and 3.8 μm, respectively. Based on the rate equation, the values ​​at Tm can be simulated. 3+ The variation of particle number density at each energy level with time under different doping concentrations is theoretically obtained as Tm. 3+ Optimal doping concentration. In this embodiment, Tm 3+ The doping concentration of the 305 doped crystal is 3 at.%, to reduce the cross-relaxation process and avoid... 3 H4 level fluorescence quenching enables efficient operation of mid-infrared continuous laser with three wavelengths.

[0078] Example 2

[0079] like Figure 3 As shown, a method based on Tm 3+ A pulsed-mode, three-wavelength mid-infrared solid-state laser with doped crystals, comprising a pump laser 101, a beam collimation and focusing system 201, an input mirror 301, and a Tm laser arranged sequentially along the optical path. 3+ Doped crystal 305, dichroic mirror 302, ~1.9μm single-wavelength output mirror 303, ~2.3μm, ~3.8μm dual-wavelength output mirror 304, and dichroic mirror 401; input mirror 301, Tm 3+ The resonant cavity is composed of a doped crystal 305, a dichroic mirror 302, a ~1.9μm single-wavelength output mirror 303, and a ~2.3μm and ~3.8μm dual-wavelength output mirror 304. The electro-optic Q-switching system is composed of a polarizer 501, an electro-optic switch 502, and a quarter-wave plate 503.

[0080] In this embodiment, the pump laser 101 is a commercial semiconductor laser with a maximum output power of 50W and an output center wavelength of 790nm.

[0081] Tm 3+The doped crystal 305 is a Tm:YLF crystal with a doping concentration of 3 at.% and a size of 3 mm × 3 mm × 10 mm. It has low phonon energy and is easy to grow into a high-quality crystal.

[0082] The input mirror 301 is a flat mirror made of CaF2 material, coated with a pump light anti-reflection film (transmittance >99.5%) and three-wavelength laser high-reflection films (reflectivity >99.8%) for ~1.9μm, ~2.3μm, and ~3.8μm.

[0083] The dichroic mirror 302 is a concave mirror with a curvature of 200mm. It is made of CaF2 material and coated with anti-reflection coatings for lasers with wavelengths of ~2.3μm and ~3.8μm (transmittance >99.5%) and high reflectivity coatings for lasers with wavelengths of ~1.9μm (reflectivity >99.8%). It is placed at an angle of 10-30° with the optical path.

[0084] The ~1.9μm single-wavelength output mirror 303 is a flat mirror made of CaF2 material, coated with a ~1.9μm wavelength laser partial transmission film, T=5%.

[0085] The ~2.3μm and ~3.8μm dual-wavelength output mirror 304 is a flat mirror made of CaF2 material, coated with a laser partial transmission film for ~2.3μm and ~3.8μm wavelengths, with T=1%.

[0086] Dichroic mirror 401 uses a CaF2 matrix crystal and is coated with a high-reflectivity film for ~2.3μm wavelength laser (reflectivity >99.8%) and a high-transmittance film for ~3.8μm wavelength laser (transmittance >99.5%). It is placed at a 45° angle with the ~2.3μm and ~3.8μm dual-wavelength output mirror 304.

[0087] The polarizer 501 uses a polarizing beam splitter prism with an extinction ratio of 1000:1.

[0088] The 1 / 4 wave plate 503 is coated with an antireflection film for laser wavelengths up to 1.9 μm, and has a transmittance of over 99.5% for laser wavelengths up to 1.9 μm.

[0089] The 502 electro-optic switch is an LN electro-optic crystal with dimensions of 9mm×9mm×25mm. It has advantages such as wide light transmission range, low hygroscopicity, and easy growth of large-size optical-grade single crystals, which is beneficial for realizing multi-wavelength pulsed laser output.

[0090] The electro-optical drive power supply provides a boost modulation signal to the electro-optical switch 502. The formula for calculating the quarter-wave voltage is as follows:

[0091]

[0092] Wherein, the external electric field electrode spacing d = 9 mm, the length of the LN electro-optic crystal along the transmission direction L = 25 mm, and the electro-optic coefficient γ 22 =6.8×10-12 For m / V, with λ0=~1.9μm, according to the Sellmeier formula, the refractive index n0 is 2.2, and the theoretical value of the quarter-wave voltage is calculated to be 2362V.

[0093] The pump light emitted by the pump laser 101 is collimated and focused by the beam collimation and focusing system 201, and then incident on Tm through the input mirror 301. 3+ In the doped crystal 305, the electro-optic Q-switching system modulates the loss of the resonant cavity to first achieve a ~1.9μm single-wavelength pulsed laser output, and then forms a three-wavelength laser cascade oscillation. The generated pulsed lasers are output through a ~1.9μm single-wavelength output mirror and a ~2.3μm and ~3.8μm dual-wavelength output mirror, respectively.

[0094] Example 3

[0095] A Tm-based 3+ The operating methods of a pulsed-mode three-wavelength mid-infrared solid-state laser with doped crystals include:

[0096] The pump light emitted by the commercial semiconductor pump laser 101, with a maximum output power of 50W and an output center wavelength of 790nm, is incident on Tm after passing through the beam collimation and focusing system 201. 3+ On the doped crystal 305, a structure consisting of an input mirror 301 and a Tm is constructed. 3+ The composite dual cavity consists of a doped crystal 305, a dichroic mirror 302, a ~1.9μm single-wavelength output mirror 303, and a ~2.3μm and 3.9μm dual-wavelength output mirror 304. The dichroic mirror is placed at an angle of 10-30° to the optical path. The cavity length, cavity mirror parameters, and output mirror transmittance are optimized to achieve the highest continuous output power of the three wavelengths.

[0097] The polarizing beam splitter 501, the LN electro-optic switch 502 and the quarter-wave plate 503 were sequentially placed in the resonant cavity, and the structure of each part was finely adjusted to optimize the continuous output power to the maximum.

[0098] Rotate the quarter-wave plate until no more light is emitted, turn on the electro-optic drive power supply, which provides a boost modulation signal to the electro-optic switch, adjusts it to the voltage corresponding to the ~1.9μm laser, and realizes the pulse output of the ~1.9μm wavelength laser;

[0099] Based on the energy level modulation method of multi-wavelength cascade oscillation, by changing the pump power, fine-tuning each component, and selecting the optimal output mirror transmittance, pulsed output of lasers with wavelengths of ~2.3μm and ~3.8μm can be achieved.

[0100] The dichroic mirror enables the splitting of pulsed laser light with wavelengths of ~2.3μm and ~3.8μm.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method based on Tm 3+ A three-wavelength mid-infrared solid-state laser with doped crystal, characterized in that, The three-wavelength mid-infrared solid-state laser includes a pump laser, a beam collimation and focusing system, a resonant cavity, and a dichroic mirror arranged along the optical path; the resonant cavity includes an input mirror, a Tm mirror, and a Tm mirror arranged sequentially along the optical path. 3+ Doped crystal, dichroic mirror, ~2.3 μm and ~3.8 μm dual-wavelength output mirror; The dichroic mirror is positioned at Tm. 3+ The doped crystal is positioned between the ~2.3 μm and ~3.8 μm dual-wavelength output mirrors, with the dichroic mirror placed at an angle of 10-30° to the optical path, and the ~1.9 μm single-wavelength output mirror is positioned on one side of the dichroic mirror.

2. The three-wavelength mid-infrared solid-state laser as described in claim 1, characterized in that, An electro-optic Q-switching system is provided in the resonant cavity. The electro-optic Q-switching system is located between the dichroic mirror and the ~1.9 μm single-wavelength output mirror. The electro-optic Q-switching system includes a polarizer, an electro-optic switch, and a quarter-wave plate arranged sequentially along the optical path.

3. The three-wavelength mid-infrared solid-state laser as described in claim 1, characterized in that, The pump laser includes a semiconductor laser or a Ti:sapphire laser, and the operating wavelength of the pump laser is 770-800 nm, with a maximum output power of 50 W.

4. The three-wavelength mid-infrared solid-state laser as described in claim 3, characterized in that, The pump laser is equipped with a semiconductor cooler for temperature control.

5. The three-wavelength mid-infrared solid-state laser as described in claim 1, characterized in that, The Tm 3+ Tm in doped crystals 3+ The doping concentration is 1.5-3 at.%, and the Tm 3+ Doped crystals include Tm 3+ Fluoride-doped crystals or Tm 3+ Doped sesquioxide crystals.

6. The three-wavelength mid-infrared solid-state laser as described in claim 5, characterized in that, The Tm 3+ Fluoride-doped crystals include Tm:YLF or Tm:LLF, wherein Tm 3+ Doped sesquioxide crystals include Tm:CaF2 or Tm:Lu2O3.

7. The three-wavelength mid-infrared solid-state laser as described in claim 1, characterized in that, The dichroic mirror is made of CaF2 or ZnSe material and is coated with a dual-wavelength laser antireflection film with a transmittance of >99.5% at ~2.3 μm and ~3.8 μm, and a high-reflection laser film with a reflectance of >99.8% at ~1.9 μm wavelength, and forms an angle of 10-30° with the optical path. Alternatively, the ~1.9 μm single-wavelength output mirror is a flat mirror made of CaF2 or ZnSe material, coated with a ~1.9 μm wavelength laser partial transmission film, with T=5%-10%; Alternatively, the ~2.3 μm and ~3.8 μm dual-wavelength output mirror is a flat mirror made of CaF2 or ZnSe material, coated with a ~2.3 μm and ~3.8 μm wavelength laser partial transmission film, T=1%-5%.

8. The three-wavelength mid-infrared solid-state laser as described in claim 1, characterized in that, The dichroic mirror is made of CaF2 or ZnSe matrix crystal material, coated with a high-reflectivity film for ~2.3 μm wavelength laser with a reflectivity >99.8% and a high-transmittance film for ~3.8 μm wavelength laser with a transmittance >99.5%, and is placed at a 45° angle with the ~2.3 μm and ~3.8 μm dual-wavelength output mirror.

9. The three-wavelength mid-infrared solid-state laser as described in claim 2, characterized in that, The polarizer has high transmittance for p-polarized lasers and high reflectivity for s-polarized lasers.

10. The three-wavelength mid-infrared solid-state laser as described in claim 9, characterized in that, The polarizer includes a polarizing beam splitter or a YAG sheet placed at Brewster angle.

11. The three-wavelength mid-infrared solid-state laser as described in claim 2, characterized in that, The quarter-wave plate is coated with an anti-reflection film for ~1.9 μm laser wavelength, and has a transmittance of over 99.5% for ~1.9 μm laser wavelength; Alternatively, the electro-optical switch may be a boost voltage switch.

12. The three-wavelength mid-infrared solid-state laser as described in claim 11, characterized in that, The electro-optic switch provides a boosted modulation signal via an electro-optic drive power supply.

13. A method based on Tm as described in any one of claims 1-12 3+ The operating method of a three-wavelength mid-infrared solid-state laser with doped crystals, characterized in that, Includes the following steps: The pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then enters the Tm through the input mirror. 3+ The doped crystal first achieves ~1.9 μm laser output in the resonant cavity, and then forms a three-wavelength laser cascade oscillation. The generated continuous laser is output through the ~1.9 μm single-wavelength output mirror and the ~2.3 μm and ~3.8 μm dual-wavelength output mirrors, respectively. Alternatively, the pump light emitted by the pump laser is collimated and focused by the beam collimation and focusing system, and then incident on the Tm through the input mirror. 3+ The doped crystal and the electro-optic Q-switching system modulate the resonant cavity loss to first achieve a ~1.9μm single-wavelength pulsed laser output, and then form a three-wavelength laser cascade oscillation. The generated pulsed laser is output through the ~1.9μm single-wavelength output mirror and the ~2.3 μm and ~3.8 μm dual-wavelength output mirrors, respectively.

14. The Tm-based method as described in claim 13 3+ The operating method of a three-wavelength mid-infrared solid-state laser with doped crystals, characterized in that, The electro-optic Q-switching system modulates the resonant cavity loss by comprising the following steps: Rotate the quarter-wave plate until it stops emitting light, turn on the electro-optic drive power supply, which provides a boost modulation signal to the electro-optic switch, adjust the electro-optic drive voltage, change the pump power, fine-tune various components, and select the best output mirror transmittance to achieve the optimal pulse output of ~1.9 μm wavelength laser. Then, based on the effective energy level control method of cascade oscillation, the ~2.3 μm and ~3.8 μm wavelength laser pulse operation are achieved respectively.

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