1.9 μm four-fold frequency blue light solid laser

Abstract

The application discloses a 1.9 mu m four times frequency blue light solid laser, belongs to the technical field of lasers, and utilizes LD pumped thulium doped yttrium lithium fluoride crystal and thulium doped yttrium aluminum fluoride crystal to obtain 1.9 mu m fundamental frequency laser output; the center wavelength of the output fundamental frequency light can be tuned to 1944 nm by adjusting the tilt angle of an intracavity etalon; high-power 1944 nm fundamental frequency laser output is obtained after thulium doped yttrium aluminum fluoride crystal solid amplification; and 486 nm laser output is obtained after cascade frequency doubling of a nonlinear crystal. The application realizes stable 1.9 mu m laser output by adopting mutual thermal compensation technology of positive thermal lens and negative thermal lens gain crystal, and then obtains large-energy and high-repetition-frequency blue light pulse laser by twice frequency doubling, and has the characteristics of no additional compensation of thermal effect and good output laser beam quality, and is especially suitable for application in the fields of ocean radar detection and underwater communication.

Description

Technical Field

[0001] The present invention relates to an all-solid-state laser, in particular to a 1.9μm quadruple frequency blue light solid-state laser. Background Art

[0002] In the field of laser technology, blue laser is an important visible laser light source with wide and important applications in ocean laser detection, underwater wireless optical communication, atomic laser refrigeration and biomedicine.

[0003] Currently, there are several ways to obtain blue lasers: direct output from semiconductor lasers or frequency doubling to obtain blue light has low output power and poor beam quality; the matrix material stability of upconversion lasers is poor and has a low damage threshold; the ultraviolet light pumping optical parametric oscillator method is inefficient, complex in structure, and large in size, and there is a risk of damage to the ultraviolet laser coating; the 1.9μm fiber laser quadrupled frequency is easily affected by thermal and nonlinear effects, making it difficult to obtain high-energy, high-peak-power laser output.

[0004] Frequency conversion using 1.9μm lasers is a good solution for obtaining blue lasers. Using solids as laser gain media, such as Tm:YAP, Tm:CYA, and Tm:YLF, can avoid the influence of fiber nonlinear effects and obtain high-energy, high-peak-power laser output. Tm:YAP laser crystals are negative biaxial crystals with natural birefringence properties that can eliminate some thermally induced birefringence losses, thereby withstanding higher pump power. Its refractive index temperature variation coefficient is 10.08×10 -6 K -1 , the thermal lens is a positive lens when working. Tm:YLF laser crystal is anisotropic crystal, and its refractive index temperature variation coefficient π direction is -4.3×10 -6 K -1 , σ direction is -2.0×10 -6 K -1 , the thermal lens is a negative lens when working.

[0005] This invention uses a laser diode (LD) to pump an oscillator made of Tm:YLF and Tm:YAP crystals. After Q-switching with an AOM (acousto-optic modulator), a pulsed 1944nm laser is generated. After Tm:YAP solid-state power amplification, a high-power 1944nm laser output is obtained. Finally, LBO crystal cascade frequency multiplication is used to generate a 486nm blue laser pulse output. This laser has the advantages of requiring no additional thermal compensation, being compact, having high peak power, and excellent beam quality. Summary of the Invention

[0006] The purpose of the present invention is to solve the shortcomings of existing high-power blue lasers, such as the need for thermal compensation, low overall conversion efficiency, and complex structure, and to provide a 486nm blue pulse laser solution that does not require compensation for thermal effects, is miniaturized, and has a compact structure.

[0007] The basic principle of the present invention is to utilize the properties of the negative temperature coefficient of the refractive index of the Tm:YLF crystal and the positive temperature coefficient of the refractive index of the Tm:YAP crystal, and to address the fact that the 1.9μm quasi-three-level laser is significantly affected by the thermal effect. The invention obtains 1.9μm fundamental frequency laser output without compensating for the thermal effect, and by adjusting the tilt angle of the etalon in the cavity, tunes the output fundamental frequency light wavelength to 1944nm. The invention combines solid-state laser power amplification technology with nonlinear crystal cascade frequency doubling technology to obtain high-peak power blue laser pulse output.

[0008] The technical solution of the present invention is:

[0009] The 1.9μm quadruple frequency blue solid-state laser includes a laser resonant cavity branch, a laser amplifier branch, and a laser nonlinear frequency conversion branch. The laser resonant cavity branch and the laser amplifier branch are 1944nm laser branches, and the laser nonlinear frequency conversion branch is a 486nm laser output branch.

[0010] The laser resonant cavity branch includes a first pump source, a first pump coupling lens group, a first cavity mirror, a first laser crystal, a second laser crystal, a first optical path reflector, a Q-switched crystal, a first etalon, a second etalon, a second cavity mirror, a second pump coupling lens group, and a second pump source;

[0011] The performance parameters and positional relationships of the above components are as follows:

[0012] The first pump source and the second pump source are any one of the fiber-coupled output laser diodes with an output center wavelength of 792 nm, the center wavelength of which corresponds to the absorption peak of Tm:YLF crystal and Tm:YAP crystal. The pump light of the first pump source and the second pump source is collimated and focused by the first pump coupling lens group and the second pump coupling lens group respectively. The first pump coupling lens group and the second pump coupling lens group are both coated with an anti-reflection film for the pump light wavelength of 780 to 800 nm and a high-reflection film of 1944 nm to prevent the laser from entering the laser diode. The focused pump light is respectively collimated and focused by the first pump coupling lens group and the second pump coupling lens group. The first cavity mirror and the first optical path reflector enter the first laser crystal and the second laser crystal, and the first cavity mirror and the first optical path reflector are coated with a 780-800nm ​​anti-reflection film and a 1944nm high-reflection film, so that the focus of the pump light is located in the first laser crystal and the second laser crystal respectively; the first cavity mirror, the second cavity mirror, the first laser crystal and the second laser crystal constitute a resonant cavity; the first laser crystal is an a-axis cut Tm:YLF crystal, the c-axis is parallel to the resonant cavity plane, and the two light-transmitting surfaces of the crystal are coated with 780-800nm ​​and 1944nm anti-reflection films, and the Tm:YLF crystal has a 1944nm high-reflection film and a 780-800nm ​​high-reflection film. 4 F4→ 3 The H6 transition generates a 1.9μm laser. The second laser crystal is an a-axis cut Tm:YAP crystal with the c-axis parallel to the resonant cavity plane. The two light-transmitting surfaces are coated with 780-800nm ​​and 1944nm anti-reflection films. The first laser crystal and the second laser crystal generate 1.9μm infrared laser under the excitation of 792nm pump light. The 1.9μm infrared laser generates a 1.9μm nanosecond laser pulse after passing through the Q-switched crystal, and then passes through the first and second etalons in sequence to narrow the line width and tune the wavelength. Finally, it passes through the The second cavity mirror outputs fundamental frequency light with a wavelength of 1944nm; the Q-switched crystal is an acousto-optic Q-switched switch, used to generate 1944nm nanosecond laser pulses, and is coated with a 1944nm anti-reflection film; the first and second etalon are placed perpendicular to the oscillating laser in the cavity, and by adjusting their tilt angles, the central wavelength of the laser output from the resonant cavity is tuned to 1944nm, while the linewidth is narrowed, which helps to improve the frequency doubling efficiency; the 1944nm laser generated by the resonant cavity is output through the second cavity mirror and enters the laser amplification branch.

[0013] The laser amplifier branch includes a second optical path reflector, a third pump source, a third pump coupling lens group, a third laser crystal, a fourth laser crystal, a third optical path reflector, a fourth pump source, and a fourth pump coupling lens group;

[0014] The performance parameters and positional relationships of the above components are as follows:

[0015] The 1944nm fundamental frequency laser enters the third laser crystal and the fourth laser crystal after passing through the second optical path reflector and is further amplified through the stimulated emission process; the third pump source and the fourth pump source are any one of the fiber-coupled output laser diodes with an output center wavelength of 792nm, and the pump light is collimated and focused by the third pump coupling lens group and the fourth pump coupling lens group. The pump coupling lens group is coated with an anti-reflection film for the pump light wavelength of 780-800nm ​​and an anti-reflection film for 1944nm. The focused pump light enters the third laser crystal and the fourth laser crystal respectively through the second optical path reflector and the third optical path reflector. The second optical path reflector and the third optical path reflector are collimated and focused by the third pump coupling lens group and the fourth pump coupling lens group. The optical path reflector is coated with a 780-800nm ​​anti-reflection coating and a 1944nm high-reflection coating. The pump light focus is located in the third laser crystal and the fourth laser crystal respectively. The third laser crystal and the fourth laser crystal are both a-axis cut Tm:YAP crystals with their c-axes parallel to the resonant cavity plane. The two light-transmitting surfaces of the crystals are coated with a 780-800nm ​​anti-reflection coating and a 1944nm anti-reflection coating. The pump light provides energy for the stimulated emission process of the 1944nm laser when it passes through the third laser crystal and the fourth laser crystal, thereby increasing the power density of the 1944nm laser. After power amplification, the 1944nm laser light serves as the fundamental frequency light and enters the nonlinear frequency conversion branch after passing through the third optical path reflector.

[0016] The laser nonlinear frequency conversion branch includes a fourth optical path reflector, a first frequency doubling crystal, a first beam splitter, a second frequency doubling crystal, and a second beam splitter. The performance parameters and positional relationships of the above components are as follows:

[0017] The first frequency-doubling crystal is a type I phase-matched lithium triborate (LBO) crystal. The two light-transmitting surfaces of the crystal are coated with 1944nm and 972nm antireflection films. According to the phase matching condition 1944nm+1944nm→972nm, the cutting angle of the LBO crystal is calculated to be θ=90°. The fundamental frequency light passes through the frequency doubling crystal to obtain a 972nm frequency doubling light output. The 972nm frequency doubling light is split by the first beam splitter and then passes through the second frequency doubling crystal. The second frequency doubling crystal is coated with a 972nm and 486nm high-transmittance film. According to the phase matching condition 972nm+972nm→486nm, the cutting angle of the LBO crystal is calculated to be θ=90°. The 486nm frequency-doubled light is output through the second beam splitter.

[0018] The present invention has the following advantages:

[0019] 1. In view of the fact that the output characteristics of 1.9μm quasi-three-level lasers are greatly affected by thermal effects, two laser crystals, Tm:YLF and Tm:YAP, are pumped by LD. The positive and negative thermal lenses generated by the two gain crystals compensate each other to achieve high-beam-quality 1.9μm laser output. No additional thermal compensation is required for the oscillator. Through the combination of dual etalons, the output wavelength of the laser can be tuned and the linewidth can be narrowed to obtain 1944nm laser.

[0020] 2. Effectively increase the power density of fundamental frequency light through solid-state laser power amplification, thereby achieving high frequency doubling efficiency;

[0021] 3. Using acousto-optic Q-switching, high-peak-power nanosecond pulse lasers can be obtained, meeting the requirements of ocean lidar and laser communication systems for high-power laser output, and improving the detection sensitivity and signal quality of the system. At the same time, the repetition frequency and timing of the output laser pulses are controllable, with high stability, facilitating modulation and data transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the optical path of the 1.9μm frequency quadrupled blue solid laser of the present invention. DETAILED DESCRIPTION

[0023] The technology of the present invention is further described below in conjunction with the implementation methods and drawings, but this should not limit the scope of protection of the present invention.

[0024] The laser's resonant cavity in the present invention achieves high-beam-quality 1.9μm laser output through mutual compensation of the positive and negative thermal lenses generated by two gain crystals. The etalon set is used to tune the central wavelength of the output laser and narrow the linewidth, which helps to improve the laser's frequency doubling efficiency. The solid laser gain medium is used to amplify the power of the fundamental frequency light and increase its power density. Finally, through cascade frequency doubling by an LBO crystal, a 486nm blue laser pulse output is obtained.

[0025] like Figure 1 As shown, the 1.9μm frequency quadrupled blue solid-state laser of the present invention is characterized in that its structure includes a laser resonator branch 1, a laser amplifier branch 2, and a laser nonlinear frequency conversion branch 3. The positional relationship of the above components is as follows:

[0026] The laser resonant cavity branch 1 includes a first pump source 1-1, a first pump coupling lens group 1-2, a first cavity mirror 1-3, a first laser crystal 1-4, a second laser crystal 1-5, a first optical path reflector 1-6, a Q-switched crystal 1-7, a first etalon 1-8, a second etalon 1-9, a second cavity mirror 1-10, a second pump coupling lens group 1-11, and a second pump source 1-12. The parameters of each component are as follows:

[0027] The first pump source 1-1 and the second pump source 1-12 are 792nm fiber-coupled output laser diodes;

[0028] The first pump coupling lens group 1-2 and the second pump coupling lens group 1-11 are coated with an anti-reflection film for the pump light wavelength of 780-800nm;

[0029] The first cavity mirror 1-3 and the first optical path reflector 1-6 are coated with a 780-800nm ​​anti-reflection film and a 1944nm high-reflection film;

[0030] The first laser crystal 1-4 is an a-axis cut Tm:YLF crystal with a crystal size of 3mm×3mm×10mm. 3+ The doping concentration is 3at.%, and the two transparent surfaces of the crystal are coated with 780-800nm ​​and 1944nm anti-reflection films. 4 F4→ 3 H6 transition produces 1.9μm laser;

[0031] The second laser crystal 1-5 is an a-axis cut Tm:YAP crystal with a crystal size of 3mm×3mm×10mm. 3+ The doping concentration is 3 at.%, and the two light-transmitting surfaces of the crystal are coated with 780-800 nm and 1944 nm antireflection films;

[0032] The Q-switched crystal 1-7 has a clear aperture of 4 mm, an operating wavelength of 1900 to 2100 nm, a loaded ultrasonic frequency of 40.68 MHz, and a modulation frequency of 100 Hz;

[0033] The first etalon 1-8 is made of fused quartz with a thickness of 0.2 mm;

[0034] The second etalon 1-9 is made of fused quartz and has a thickness of 0.05 mm;

[0035] The laser amplifier branch 2 includes a second optical path reflector 2-1, a third pump source 2-3, a third pump coupling lens group 2-2, a third laser crystal 2-4, a fourth laser crystal 2-5, a third optical path reflector 2-6, a fourth pump source 2-8, and a fourth pump coupling lens group 2-7;

[0036] The third pump source 2-3 and the fourth pump source 2-8 are 792nm fiber-coupled output laser diodes;

[0037] The third pump coupling lens group 2-2 and the fourth pump coupling lens group 2-7 are coated with an anti-reflection film for the pump light wavelength of 780-800nm;

[0038] The third laser crystal 2-4 is an a-axis cut Tm:YAP crystal with a crystal size of 4mm×4mm×10mm. 3+ The doping concentration is 3at.%, and the two light-transmitting surfaces of the crystal are coated with a 780-800nm ​​antireflection film and a 1944nm antireflection film;

[0039] The fourth laser crystal 2-5 is an a-axis cut Tm:YAP crystal with a crystal size of 4mm×4mm×10mm. 3+ The doping concentration is 3at.%, and the two light-transmitting surfaces of the crystal are coated with a 780-800nm ​​antireflection film and a 1944nm antireflection film;

[0040] The laser nonlinear frequency conversion branch 3 includes a fourth optical path reflector 3-1, a first frequency doubling crystal 3-2, a first beam splitter 3-3, a second frequency doubling crystal 3-4, and a second beam splitter 3-5;

[0041] The performance parameters of the above components are as follows:

[0042] The first frequency doubling crystal 3-2 is a type I phase-matched lithium triborate LBO crystal with a crystal size of 4mm×4mm×12mm. The two 4mm×4mm light-transmitting surfaces of the crystal are coated with 1944nm and 972nm antireflection films. The crystal cutting angle is θ=90°.

[0043] The second frequency-harmonic crystal 3-4 is a phase-matched lithium triborate LBO crystal with a crystal size of 4mm×4mm×12mm. The two 4mm×4mm light-transmitting surfaces of the crystal are coated with 972nm and 486nm anti-reflection films. The crystal cutting angle is θ=90°.

[0044] The first beam splitter 3-3 is coated with a 1944nm high reflection film and a 972nm high transmission film;

[0045] The second beam splitter 3-5 is coated with a 972nm high reflection film and a 486nm high transmission film;

[0046] In summary, the present invention has the characteristics of no need for additional compensation for thermal effects and good output laser beam quality. The laser is small in size and compact in structure, and can obtain high-peak power 486nm nanosecond pulsed blue light laser output, which is particularly suitable for applications in fields such as marine radar detection and underwater communications.

[0047] The above embodiments are intended only to illustrate the technical features of the present invention and should not be construed to limit the scope of protection of the present invention. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. 1.9μm frequency quadrupled blue solid-state laser, characterized by: It includes a laser resonant cavity branch (1), a laser amplifier branch (2), and a laser nonlinear frequency conversion branch (3); The laser resonant cavity branch (1) comprises a first pump source (1-1), a first pump coupling lens group (1-2), a first cavity mirror (1-3), a first laser crystal (1-4), a second laser crystal (1-5), a first optical path reflector (1-6), a Q-switched crystal (1-7), a first etalon (1-8), a second etalon (1-9), a second cavity mirror (1-10), a second pump coupling lens group (1-11), and a second pump source (1-12); The 792nm pump light generated by the first pump source (1-1) and the second pump source (1-12) is collimated and focused by the first pump coupling lens group (1-2) and the second pump coupling lens group (1-11), respectively. The focused pump light enters the first laser crystal (1-4) and the second laser crystal (1-5) respectively through the first cavity mirror (1-3) and the first optical path reflector (1-6). The focus of the pump light is located in the first laser crystal (1-4) and the second laser crystal (1-5). 5) generating 1.9 μm laser light under pump light excitation, generating 1.9 μm nanosecond laser pulses after passing through a Q-switched crystal (1-7), then sequentially passing through a first etalon (1-8) and a second etalon (1-9) to tune the wavelength and narrow the linewidth, and outputting fundamental frequency light with a central wavelength of 1944 nm through a second cavity mirror (1-10), wherein the 1944 nm nanosecond laser pulse oscillates between the first cavity mirror (1-3) and the second cavity mirror (1-10), and the first etalon (1-8) and the second etalon (1-9) are placed perpendicular to the oscillating laser light in the cavity; The laser amplifier branch (2) comprises a second optical path reflector (2-1), a third pump source (2-3), a third pump coupling lens group (2-2), a third laser crystal (2-4), a fourth laser crystal (2-5), a third optical path reflector (2-6), a fourth pump source (2-8), and a fourth pump coupling lens group (2-7); The 792nm pump light generated by the third pump source (2-3) and the fourth pump source (2-8) is collimated and focused by the third pump coupling lens group (2-2) and the fourth pump coupling lens group (2-7), respectively. The focused pump light enters the third laser crystal (2-4) and the fourth laser crystal (2-5) respectively through the second optical path reflector (2-1) and the third optical path reflector (2-6), and the focus of the pump light is located in the third laser crystal (2-4) and the fourth laser crystal (2-5), respectively. The third laser crystal (2-4) and the fourth laser crystal (2-5) amplify the power of the fundamental frequency light with a wavelength of 1944nm output from the second cavity mirror (1-10) and reflected by the second optical path reflector (2-1), and the obtained high-power 1944nm fundamental frequency light is output from the third optical path reflector (2-6); The laser nonlinear frequency conversion branch (3) comprises a fourth optical path reflector (3-1), a first frequency doubling crystal (3-2), a first beam splitter (3-3), a second frequency doubling crystal (3-4), and a second beam splitter (3-5); The high-power 1944nm fundamental frequency laser output by the third optical path reflector (2-6) is reflected by the fourth optical path reflector (3-1) and then passes through the first frequency doubling crystal (3-2) to generate 972nm laser. The first beam splitter (3-3) separates the 972nm frequency doubling light from the 1944nm fundamental frequency light. The separated 972nm laser passes through the second frequency doubling crystal (3-4) to generate 486nm laser. The second beam splitter (3-5) separates the 486nm laser from the 972nm laser, and finally obtains 486nm laser output.

2. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first pump source (1-1), the second pump source (1-12), the third pump source (2-3) and the fourth pump source (2-8) are fiber-coupled output laser diodes with an output center wavelength of 792 nm.

3. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first pump coupling lens group (1-2), the second pump coupling lens group (1-11), the third pump coupling lens group (2-2), and the fourth pump coupling lens group (2-7) are plated with a 780-800nm ​​anti-reflection film and a 1944nm high-reflection film.

4. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first cavity mirror (1-3), the first light path reflector (1-6), the second light path reflector (2-1), and the third light path reflector (2-6) are plated with a 780-800nm ​​anti-reflection film and a 1944nm high-reflection film.

5. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The second cavity mirror (1-10) is coated with a 1944nm partially transparent film with a transmittance of 20% to 50%.

6. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first laser crystal (1-4) is an a-axis cut thulium-doped yttrium aluminate (Tm:YAP) crystal, the c-axis of the crystal is parallel to the (1-10) resonant cavity plane between the first cavity mirror (1-3) and the second cavity mirror, and the two light-transmitting surfaces of the crystal are coated with 780-800nm ​​and 1944nm anti-reflection films.

7. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The second laser crystal (1-5) is an a-axis cut thulium-doped yttrium fluoride (Tm:YLF) crystal, the c-axis of the crystal is parallel to the (1-10) resonant cavity plane between the first cavity mirror (1-3) and the second cavity mirror, and the two light-transmitting surfaces of the crystal are coated with 780-800nm ​​and 1944nm anti-reflection films.

8. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The Q-switched crystal (1-7) is coated with a 1944nm anti-reflection film.

9. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The materials of the first etalon (1-8) and the second etalon (1-9) are fused quartz and are not coated.

10. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The third laser crystal (2-4) and the fourth laser crystal (2-5) are thulium-doped yttrium aluminate crystals, coated with 780-800nm ​​and 1944nm anti-reflection films.

11. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first frequency doubling crystal (3-2) is a type I phase-matched lithium triborate LBO crystal, the two light-transmitting surfaces of which are coated with 1944nm and 972nm antireflection films, and the cutting angles thereof are θ=90° and φ=26.4°.

12. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The second frequency-doubling crystal (3-4) is a type I phase-matched lithium triborate LBO crystal, the two light-transmitting surfaces of which are coated with 972nm and 486nm antireflection films, and the cutting angles are θ=90° and φ=17.5°.

13. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The first beam splitter (3-3) is coated with a 1944nm high-reflection film and a 972nm anti-reflection film.

14. The 1.9 μm frequency quadrupled blue solid-state laser according to claim 1, characterized in that: The second beam splitter (3-5) is coated with a 972nm high reflection film and a 486nm anti-reflection film.

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