An air-cooled micro single-frequency laser based on a ring cavity

Abstract

The present invention discloses an air-cooled micro single-frequency laser based on a ring cavity, belonging to the technical field of solid laser technology. In the laser, a first diode single tube and a second diode single tube are arranged on both sides of a laser crystal to generate two light sources. Among them, the first light source successively passes through a first fast-axis collimating lens, a first shaping lens, and a first resonant cavity mirror to reach the laser crystal, and the second light source successively passes through a second fast-axis collimating lens, a second shaping lens, and a second resonant cavity mirror to reach the laser crystal; a λ / 2 wave plate, a Faraday rotator, and a thin-film polarizer together form an optical diode, which together with the first resonant cavity mirror, the second resonant cavity mirror, and the third resonant cavity mirror form a ring resonator, so that the laser light source reaching the laser crystal oscillates in the ring resonator. The repetition frequency of the present invention can reach several kilohertz, and the whole machine is packaged by semiconductor technology, with high reliability and ultra-high volume compactness.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lasers, and particularly relates to an air-cooled micro single-frequency laser based on a ring cavity. Background Art

[0002] The application prospect of mid-infrared photoacoustic spectroscopy is attractive. It can be used for trace gas detection and analysis in environmental, industrial process or medical diagnosis processes, with high sensitivity, wide dynamic range and fast response. Relying on a high-performance and highly reliable mid-infrared pulsed laser light source with selectable wavelengths, it has become the most reliable technical approach to use a near-infrared single-longitudinal-mode pulsed laser to pump a periodically poled crystal. If based on the optical parametric oscillation process of signal light and idler light double resonance, a near-infrared single-frequency pump source with a single-pulse energy of only hundreds of microjoules can meet the oscillation threshold of the parametric process without dozens or even hundreds of millijoules.

[0003] The parametric oscillation technology uses the second-order nonlinear optical effect of a periodically poled crystal to achieve laser frequency down-conversion. Based on polarization period and temperature tuning, parametric laser output at any wavelength can be realized. The incident pump light energy is emitted in the form of optical radiation (signal light and idler light), without waste heat generation. The parametric oscillation adopts a signal light and idler light double resonance scheme to reduce the near-infrared pulsed laser pump threshold, so that it becomes possible to achieve ultra-high volume compactness for near-infrared pulsed lasers. However, the current near-infrared single-frequency pulsed laser pump sources rely on two technical approaches. One is continuous single-frequency seed fiber pulse modulation and fiber pre-amplification. The peak power density of the laser pulse is relatively high at a relatively narrow pulse width. Limited by the nonlinear effect of fiber devices, the single-pulse energy output is only a few microjoules. To obtain hundreds of microjoules, a solid-state amplifier must be cascaded at the rear stage for solid-state amplification, which means very poor volume compactness. The other is to inject a continuous single-frequency seed source into a resonant cavity for resonant amplification, which can achieve a single-frequency pulsed laser output of several millijoules. However, the length of the resonant cavity often reaches hundreds of millimeters, the spatial volume compactness is very poor, and the locking technology is often very complex, with high implementation costs. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides an air-cooled micro single-frequency laser based on a ring cavity, which generates a fully solid-state near-infrared single-frequency pulsed laser based on a single diode and ring cavity technology. The whole machine is packaged by semiconductor technology, with high reliability and ultra-high volume compactness.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] An air-cooled micro single-frequency laser based on a ring cavity, comprising a first single diode, a first fast-axis collimating lens, a first shaping lens, a first resonant cavity mirror, a third resonant cavity mirror, a λ / 2 wave plate, a Faraday rotator, a thin-film polarizer, a laser crystal, a second resonant cavity mirror, a second shaping lens, a second fast-axis collimating lens, and a second single diode. Among them,

[0007] The first single diode and the second single diode are arranged on both sides of the laser crystal to generate two light sources. Among them, the first light source passes through the first fast-axis collimating lens, the first shaping lens, and the first resonant cavity mirror in sequence to reach the laser crystal, and the second light source passes through the second fast-axis collimating lens, the second shaping lens, and the second resonant cavity mirror in sequence to reach the laser crystal;

[0008] The λ / 2 wave plate, the Faraday rotator, and the thin-film polarizer together constitute an optical diode, and the optical diode and the first resonant cavity mirror, the second resonant cavity mirror, and the third resonant cavity mirror together constitute a ring resonator, so that the laser light source reaching the laser crystal oscillates in the ring resonator and is output through the thin-film polarizer.

[0009] The beneficial effects of the present invention are as follows:

[0010] Based on the single diode and ring cavity technologies, the present invention realizes a near-infrared single-longitudinal-mode pulsed laser pump source with high reliability and ultra-high volume compactness. The overall size of the machine is only dozens of millimeters, the thermal power is only dozens of watts, the output laser pulse width is about dozens of nanoseconds, which is beneficial to further improving the single-pulse energy based on a solid-state amplifier. The repetition frequency can reach several kilohertz, the linewidth reaches the Fourier transform limit, and the whole machine is packaged with ultra-high stability by semiconductor technology and can withstand high and low temperature cycling and vibration shock, providing a near-infrared single-longitudinal-mode pulsed pump source with ultra-high reliability and ultra-volume compactness for mid-infrared optical parametric oscillation. Description of the Drawings

[0011] Figure 1 is a structural diagram of an air-cooled micro single-frequency laser based on a ring cavity according to the present invention;

[0012] Figure 2 is a schematic diagram of the packaging structure of an air-cooled micro single-frequency laser based on a ring cavity according to the present invention.

[0013] Reference Signs:

[0014] 1. First single diode; 2. First fast-axis collimating lens; 3. First shaping lens; 4. First resonant cavity mirror; 5. Passive Q-switching crystal; 6. Third resonant cavity mirror; 7. λ / 2 wave plate; 8. Faraday rotator; 9. Thin-film polarizer; 10. Laser crystal; 11. Second resonant cavity mirror; 12. Second shaping lens; 13. Second fast-axis collimating lens; 14. Second single diode; 15. Gold-plated sealed housing; 16. First gold-plated ceramic; 17. First semiconductor cooler; 18. Second gold-plated ceramic; 19. Third gold-plated ceramic; 20. Fourth gold-plated ceramic; 21. First mounting screw; 22. Second mounting screw; 23. First heat-insulating washer; 24. Second heat-insulating washer; 25. Heat dissipation fins; 26. Second semiconductor cooler. Detailed implementation mode

[0015] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0016] As Figure 1 shown, it is a structural diagram of an air-cooled micro single-frequency laser based on a ring cavity according to the present invention. The first single diode 1 and the second single diode 14 are the pump sources of the air-cooled micro single-frequency laser, which are arranged on both sides of the laser crystal 10 to generate two light sources. The pump power is only 10W, the size of the light-emitting area in the slow axis direction is 200μm, the fast axis direction is 1μm, the spectral full width at half maximum ≤ 3nm, the divergence angle in the slow axis direction is 5°, the divergence angle in the fast axis direction is 30°, the polarization mode is TE, and the wavelength drift coefficient is about 0.28nm / °C. Among them, the first light source passes through the first fast-axis collimating lens 2, the first shaping lens 3, and the first resonant cavity mirror 4 in sequence to reach the laser crystal 10. The second light source passes through the second fast-axis collimating lens 13, the second shaping lens 12, and the second resonant cavity mirror 11 in sequence to reach the laser crystal 10. The λ / 2 wave plate 7, the Faraday rotator 8, and the thin-film polarizer 9 together constitute an optical diode. The optical diode and the first resonant cavity mirror 4, the second resonant cavity mirror 11, and the third resonant cavity mirror 6 together constitute a ring resonator, so that the laser light source reaching the laser crystal 10 oscillates in the ring resonator. In particular, the first resonant cavity mirror 4, the second resonant cavity mirror 11, the third resonant cavity mirror 6, and the thin-film polarizer 9 are all incident and exit at 45° to form a complete ring resonator.

[0017] The first fast-axis collimating lens 2 and the second fast-axis collimating lens 13 respectively perform angle compression on the laser beams emitted by the first single diode 1 and the second single diode 14 in the fast-axis direction. The first single diode 1 and the second single diode 14 are packaged in the COS form. The first fast-axis collimating lens 2 and the second fast-axis collimating lens 13 are respectively closely attached to the light-emitting ends of the first single diode 1 and the second single diode 14. The other ends of the first single diode 1 and the second single diode 14 are bonded to the first gold-plated ceramic 16 to achieve highly reliable compression and collimation of the divergence angle in the fast-axis direction. Since the distance between the two is very sensitive, on-line measurement and bonding are often carried out based on precise control.

[0018] The first shaping lens 3 and the second shaping lens 12 respectively focus the laser beams after angle compression to meet the requirements of the resonant cavity mode size oscillation.

[0019] The first resonant cavity mirror 4 and the second resonant cavity mirror 11 respectively receive the two focused light sources to achieve round-trip gain reflection of the oscillating laser, and the coating is highly reflective for the oscillating laser.

[0020] The passive Q-switching crystal 5 realizes compact Q-switching, achieving high-peak-power pulsed laser oscillation and output. Since the pumping mechanisms of the first single diode 1 and the second single diode 14 are continuous pumping, the population inversion density during the energy storage stage exponentially increases from zero. After meeting the laser oscillation threshold corresponding to the small-signal transmittance of the passive Q-switching crystal 5, the population inversion density is converted into laser output, and the laser starts to oscillate, achieving laser output of dozens of nanoseconds. A slight residue of the population inversion density remains, and the exponential gain process is repeated again for the next energy extraction process.

[0021] The λ / 2 wave plate 7, the Faraday rotator 8, and the thin-film polarizer 9 together form an optical diode, enabling the laser to oscillate only counterclockwise. At the same time, by adjusting the angle of the λ / 2 wave plate 7, when the oscillating laser is reflected to the thin-film polarizer 9, the polarization state of the laser is partially s-polarized and partially p-polarized. That is, by adjusting the angle of the λ / 2 wave plate 7, the effective reflectivity of the resonant cavity can be flexibly adjusted, thereby adjusting the output laser ratio and keeping the power density in the resonant cavity at a reasonable value to avoid damage to optical components, which is easy to calculate based on the Jones matrix.

[0022] The laser crystal 10 adopts a double-single-diode double-end pumping structure, with symmetric thermal effects at both ends, and the laser oscillation gain in the ring resonator is relatively uniform, eliminating the polarization loss and spatial hole burning effect caused by thermally induced birefringence, which helps to achieve single-frequency laser oscillation.

[0023] As Figure 2 shown, it is a schematic diagram of the packaging structure of an air-cooled micro single-frequency laser based on a ring cavity according to the present invention. To avoid mode hopping in the resonant cavity, the whole machine of the laser is packaged using an ultra-high-stability semiconductor packaging process.

[0024] Among them, the first single diode 1 and the second single diode 14 are respectively welded to the upper end face of the first gold-plated ceramic 16 by gold plating. The lower end face of the first gold-plated ceramic 16 realizes ultra-high-precision temperature control of ±0.01 °C based on the first semiconductor refrigerator 17, and the mechanical stability and temperature stability ensure that the pump source hardly changes.

[0025] The laser crystal 10 adopts a double-bridge cooling structure and is welded between the second gold-plated ceramic 18 and the third gold-plated ceramic 19. Slight temperature fluctuations do not affect the length of the laser crystal. The other end of the first semiconductor refrigerator 17 and the ends of the second gold-plated ceramic 18 and the third gold-plated ceramic 19 are integrally welded to the upper end face of the fourth gold-plated ceramic 20.

[0026] To further improve the temperature stability, the whole laser is sealed in the gold-plated sealed housing 15 to isolate external long-wave radiation. The temperature control accuracy of the gold-plated sealed housing 15 is only limited by the semiconductor refrigerator and the driver. The whole laser is controlled by a two-stage semiconductor refrigerator for temperature control. The gold-plated sealed housing 15 adopts the first heat-insulating washer 23 and the second heat-insulating washer 24, and is installed on the second semiconductor refrigerator 26 and the heat dissipation fins 25 stacked up and down with the first mounting screw 21 and the second mounting screw 22. Due to the low thermal power, an air-cooled heat dissipation design can be completely adopted, and the whole machine thermal power is dissipated by the heat dissipation fins 25. Based on the above packaging process, ultra-stable and reliable packaging can be achieved.

[0027] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An air-cooled micro single-frequency laser based on a ring cavity, characterized in that, It includes a first single diode, a first fast-axis collimating lens, a first shaping lens, a first resonator mirror, a third resonator mirror, a λ / 2 wave plate, a Faraday rotator, a thin-film polarizer, a laser crystal, a second resonator mirror, a second shaping lens, a second fast-axis collimating lens, and a second single diode. Among them, the first single diode and the second single diode are arranged on both sides of the laser crystal to generate two light sources. Among them, the first light source passes through the first fast-axis collimating lens, the first shaping lens, and the first resonator mirror in sequence and reaches the laser crystal, and the second light source passes through the second fast-axis collimating lens, the second shaping lens, and the second resonator mirror in sequence and reaches the laser crystal; the λ / 2 wave plate, the Faraday rotator, and the thin-film polarizer together form an optical diode, and the optical diode and the first resonator mirror, the second resonator mirror, and the third resonator mirror together form a ring resonator, so that the laser light source reaching the laser crystal oscillates only counterclockwise in the ring resonator and is output through the thin-film polarizer; the laser adopts an air-cooled heat dissipation method, is connected to a gold-plated ceramic sheet through a semiconductor refrigerator for heat dissipation, and the whole laser is sealed in a gold-plated sealed housing.

2. The air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, The first single diode and the second single diode are the pump sources of an air-cooled micro single-frequency laser.

3. The air-cooled micro single-frequency laser based on a ring cavity according to claim 2, characterized in that, The first resonator mirror, the second resonator mirror, the third resonator mirror, and the thin-film polarizer are all incident and exit at 45°.

4. A kind of air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, The first fast-axis collimating lens and the second fast-axis collimating lens are used to compress the angles of the lasers emitted by the first single diode and the second single diode in the fast-axis direction respectively.

5. A kind of air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, The first shaping lens and the second shaping lens are used to focus the lasers after angle compression respectively.

6. The air-cooled micro single-frequency laser based on a ring cavity according to claim 1, wherein, The first resonator mirror and the second resonator mirror are used to receive the two focused light sources respectively, realize the round-trip gain reflection of the oscillating laser, and the coating is highly reflective to the oscillating laser.

7. A kind of air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, A passive Q-switching crystal is also included between the first resonator mirror and the third resonator mirror, which is used to realize compact Q-switching, high-peak-power pulsed laser oscillation and output.

8. A kind of air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, Adjust the angle of the λ / 2 wave plate to change the output laser ratio when the oscillating laser is reflected to the thin-film polarizer.

9. The air-cooled micro single-frequency laser based on a ring cavity according to claim 1, characterized in that, The first single diode and the second single diode are welded to the upper end face of the first gold-plated ceramic by gold plating respectively, and the lower end face of the first gold-plated ceramic is connected to the upper end face of the first semiconductor refrigerator; The laser crystal adopts a double-bridge cooling structure and is welded between the second gold-plated ceramic and the third gold-plated ceramic; The lower end face of the first semiconductor refrigerator, the ends of the second gold-plated ceramic and the third gold-plated ceramic are integrally welded to the upper end face of the fourth gold-plated ceramic; then the whole laser is sealed in a gold-plated sealed housing.

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