1.9 [mu] m quadruplicated frequency blue light solid laser

Abstract

A 1.9 [mu] m quadruplicated-frequency blue-light solid-state laser belongs to the technical field of lasers, 1.9 [mu] m fundamental-frequency laser output is obtained by using an LD pumping thulium-doped yttrium lithium fluoride crystal and a thulium-doped yttrium aluminate crystal, and the central wavelength of output fundamental-frequency light can be tuned to 1944 nm by adjusting the inclination angle of an etalon in a cavity. After solid amplification of the thulium-doped yttrium aluminate crystal, high-power 1944nm fundamental frequency laser output is obtained, and after cascade frequency doubling of the nonlinear crystal, 486nm laser output is obtained. 1.9 [mu] m stable laser output is realized by adopting a positive thermal lens and negative thermal lens gain crystal mutual thermal compensation technology, high-energy and high-repetition-frequency blue light pulse laser is obtained through secondary frequency doubling, and the laser has the characteristics of no need of additional compensation thermal effect and good quality of output laser beams; the method is especially suitable for the fields of ocean radar detection, underwater communication and the like.

Description

Technical Field

[0001] The 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 light laser is an important visible laser light source with wide and important applications in ocean laser detection, underwater wireless optical communications, 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 with low output power and poor beam quality; the matrix material stability of up-conversion lasers is poor and the damage threshold is low; the ultraviolet light pumping optical parametric oscillator method has low efficiency, complex structure, and large size, and there is a risk of damage to the ultraviolet laser coating; the quadrupled frequency of 1.9μm fiber lasers is easily affected by thermal and nonlinear effects, making it difficult to obtain high-energy, high-peak-power laser output.

[0004] Using 1.9μm laser for frequency conversion is a better solution to obtain blue laser. Using solid as laser gain medium, such as Tm:YAP, Tm:CYA, Tm:YLF, etc., can avoid the influence of fiber nonlinear effect and obtain high energy and high peak power laser output. Tm:YAP laser crystal is a negative biaxial crystal. Its natural birefringence characteristics can eliminate part of the thermally induced birefringence loss, so as to withstand higher power pumping. 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] The present invention uses LD pumped Tm:YLF and Tm:YAP crystal oscillators, obtains pulsed 1944nm laser after Q-switching by AOM acousto-optic modulator, obtains high-power 1944nm laser output after Tm:YAP solid power amplification, and finally obtains 486nm blue laser pulse output after LBO crystal cascade frequency doubling. The laser has the advantages of no need for additional thermal compensation, small size, high peak power and good 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: utilizing the property that the temperature coefficient of the refractive index of Tm:YLF crystal is negative and the temperature coefficient of the refractive index of Tm:YAP crystal is positive, aiming at the characteristic that the 1.9μm quasi-three-level laser is significantly affected by the thermal effect, obtaining 1.9μm fundamental frequency laser output without compensating for the thermal effect, adjusting the tilt angle of the standard tool in the cavity, tuning the output fundamental frequency light wavelength to 1944nm, combining the solid laser power amplification technology with the nonlinear crystal cascade frequency doubling technology, obtaining high peak power blue light laser pulse output.

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

[0009] The 1.9μm quadruple frequency blue light solid laser comprises a laser resonant cavity branch, a laser amplifier branch and a laser nonlinear frequency conversion branch, wherein 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 792nm, and the center wavelength 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 780-800nm ​​and a high reflection film of 1944nm 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 780-800nm ​​anti-reflection film and 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 4 F4→ 3 H6 transition generates 1.9μm laser, the second laser crystal is a Tm:YAP crystal cut on the a-axis, the c-axis is 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 1.9μm nanosecond laser pulse after passing through the Q-switched crystal, and then passes through the first etalon and the second etalon in sequence to narrow the line width and tune the wavelength, and finally passes through 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 etalon and the second etalon are placed vertically relative to the oscillating laser in the cavity, and the central wavelength of the laser output by the resonant cavity is tuned to 1944nm by adjusting their inclination angles, while narrowing the line width, 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 radiation 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, and the pump coupling lens group is plated with an anti-reflection film for the pump light wavelength of 780-800nm ​​and an anti-reflection film for 1944nm, and 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, and 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 film and a 1944nm high-reflection film, and the focus of the pump light 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, and the c-axis of the crystal is parallel to the plane of the resonant cavity, and the two light-transmitting surfaces of the crystal are coated with a 780-800nm ​​anti-reflection film and a 1944nm anti-reflection film; the pump light provides energy for the stimulated radiation process of the 1944nm laser when it passes through the third laser crystal and the fourth laser crystal, so that the power density of the 1944nm laser is increased, and the 1944nm laser after power amplification enters the nonlinear frequency conversion branch as the fundamental frequency light 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, and the two light-transmitting surfaces of the crystal are coated with 1944nm and 972nm anti-reflection 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 laser are greatly affected by thermal effects, LD is used to pump Tm:YLF and Tm:YAP laser crystals. The positive thermal lens and negative thermal lens generated by the two gain crystals compensate each other to achieve high beam quality 1.9μm laser output. The oscillator does not need additional thermal compensation. Through the combination of double standards, the output wavelength of the laser can be tuned and the line width can be narrowed to obtain 1944nm laser.

[0020] 2. Effectively improve the power density of fundamental frequency light by solid laser power amplification, thereby obtaining high frequency doubling efficiency;

[0021] 3. The acousto-optic Q-switching method can be used to obtain high-peak power nanosecond pulse lasers, which can meet the requirements of ocean lidar and laser communication systems for high-power laser output, and can improve the detection sensitivity and signal quality of the system. At the same time, the repetition rate and timing of the output laser pulses are controllable, with high stability, which is convenient for modulation and data transmission. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] The resonant cavity of the laser in the present invention compensates each other through the positive thermal lens and the negative thermal lens generated by two gain crystals, so as to achieve 1.9μm laser output with high beam quality; the etalon group is used to tune the central wavelength of the output laser and narrow the line width, which is helpful to improve the frequency doubling efficiency of the laser; the solid laser gain medium is used to amplify the power of the fundamental frequency light and improve its power density; finally, the 486nm blue light laser pulse output is obtained through LBO crystal cascade frequency doubling.

[0025] like Figure 1 As shown, the 1.9 μm quadrupled frequency blue solid laser of the present invention is characterized in that its structure includes a laser resonant cavity 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 a pump light wavelength of 780-800 nm;

[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 light aperture of 4 mm, an operating wavelength of 1900-2100 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 and has 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 a pump light wavelength of 780 to 800 nm;

[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 780-800nm ​​anti-reflection film and 1944nm anti-reflection 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 780-800nm ​​anti-reflection film and 1944nm anti-reflection 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, the crystal size is 4mm×4mm×12mm, the two 4mm×4mm light-transmitting surfaces of the crystal are coated with 1944nm and 972nm anti-reflection films, and the crystal cutting angle is θ=90°.

[0043] The second frequency doubling 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 of 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 pulse blue light laser output, which is particularly suitable for applications in the fields of marine radar detection and underwater communications.

[0047] The above embodiments are only for illustrating the technical features of the present invention and should not be used to limit the protection scope of the present invention. Any modification or replacement that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. 1.9μm quadruple frequency blue solid laser, characterized by: It comprises 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 792 nm 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 pulse after passing through a Q-switched crystal (1-7), then passing through a first etalon (1-8) and a second etalon (1-9) to tune the wavelength and narrow the line width, 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 vertically relative 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 (2-4) 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 quadruple frequency blue solid 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 central wavelength of 792 nm.

3. The 1.9 μm quadruple frequency blue solid 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 780-800nm ​​anti-reflection film and 1944nm high-reflection film.

4. The 1.9 μm quadruple frequency blue solid 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 780-800nm ​​anti-reflection film and 1944nm high-reflection film.

5. The 1.9 μm quadruple frequency blue solid 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 quadruple frequency blue solid 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 quadruple frequency blue solid 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 quadruple frequency blue solid 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 quadruple frequency blue solid 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 quadruple frequency blue solid 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 quadruple frequency blue solid 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, and the two light-transmitting surfaces of the crystal are coated with 1944nm and 972nm anti-reflection films, and the cutting angles are θ=90° and φ=26.4°.

12. The 1.9 μm quadruple frequency blue solid 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 anti-reflection films, and the cutting angles are θ=90° and φ=17.5°.

13. The 1.9 μm quadruple frequency blue solid 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 quadruple frequency blue solid 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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