Air-cooled miniature single-frequency laser based on annular cavity

Abstract

The invention discloses an air-cooled miniature single-frequency laser based on an annular cavity, and belongs to the technical field of solid laser technologies. In the laser, a first diode single tube and a second diode single tube are respectively arranged on two sides of a laser crystal to generate two paths of light sources, the first path of light source passes through a first fast axis collimating lens, a first shaping lens and a first resonant cavity reflector in sequence to reach the laser crystal, and the second path of light source passes through a second fast axis collimating lens. The second path of light source passes through a second fast axis collimating lens, a second shaping lens and a second resonant cavity reflector in sequence to reach the laser crystal; the lambda / 2 wave plate, the Faraday rotator and the thin film polarizer jointly form an optical diode, and the optical diode, the first resonant cavity reflector, the second resonant cavity reflector and the third resonant cavity reflector jointly form an annular resonant cavity, so that a laser light source reaching the laser crystal oscillates in the annular resonant cavity. The repetition frequency can reach thousands of hertz, and the whole machine is packaged by a semiconductor process, and has high reliability and ultrahigh volume compactness.

Description

Technical Field

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

[0002] Mid-infrared photoacoustic spectroscopy has attractive application prospects. It can be used for trace gas detection and analysis in the environment, industrial processes or medical diagnosis processes. It has high sensitivity, wide dynamic range and fast response. Relying on the high-performance and high-reliability mid-infrared pulse laser light source with selectable wavelength, the near-infrared single longitudinal mode pulse laser pumping periodically polarized crystal has become the most reliable technical approach. If it is based on the optical parametric oscillation process of double resonance of signal light and idler light, it does not require tens or even hundreds of millijoules. A near-infrared single-frequency pump source with a single pulse energy of only hundreds of microjoules can meet the parametric process oscillation threshold.

[0003] Parametric oscillation technology uses the second-order nonlinear optical effect of periodically polarized crystals to achieve laser frequency down-conversion. Based on the polarization period and temperature tuning, parametric laser output of any wavelength can be achieved. The incident pump light energy is emitted in the form of optical radiation (signal light and idler light), and no waste heat is generated. Parametric oscillation uses a double resonance scheme of signal light and idler light to reduce the near-infrared pulse laser pumping threshold, making it possible for near-infrared pulse lasers to achieve ultra-high volume compactness. However, the current near-infrared single-frequency pulse laser pump source relies on two technical approaches. One is continuous single-frequency seed fiber pulse modulation and fiber pre-amplification. The laser pulse peak power density is high under narrow pulse width. Limited by the nonlinear effect of fiber devices, the single pulse energy output is only a few microjoules. In order to obtain hundreds of microjoules, the back stage must be cascaded with a solid amplifier for solid amplification, which means that the volume compactness is very poor; the second is to inject a continuous single-frequency seed source into the resonant cavity to achieve resonant amplification, which can achieve a few millijoules of single-frequency pulse laser output, but the length of the resonant cavity is often hundreds of millimeters, the spatial volume compactness is very poor, and the locking technology is often very complex, and the implementation cost is high. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an air-cooled miniature single-frequency laser based on a ring cavity, which generates an all-solid-state near-infrared single-frequency pulse laser based on a single diode tube and a ring cavity technology. The whole machine is packaged using semiconductor technology and has high reliability and ultra-high compactness.

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

[0006] A ring cavity-based air-cooled micro single-frequency laser comprises a first diode single tube, a first fast axis collimating lens, a first shaping lens, a first resonant cavity reflector, a third resonant cavity reflector, a λ / 2 wave plate, a Faraday rotator, a thin film polarizer, a laser crystal, a second resonant cavity reflector, a second shaping lens, a second fast axis collimating lens, and a second diode single tube, wherein:

[0007] The first diode single tube and the second diode single tube are arranged on both sides of the laser crystal to generate two light sources, wherein the first light source passes through the first fast axis collimating lens, the first shaping lens, and the first resonant cavity reflector 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 reflector 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 reflector, the second resonant cavity reflector and the third resonant cavity reflector together constitute a ring resonant cavity, so that the laser light source reaching the laser crystal oscillates in the ring resonant cavity and then is output through the thin-film polarizer.

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

[0010] The present invention is based on diode single tube and ring cavity technology to achieve a near-infrared single longitudinal mode pulse laser pump source with high reliability and ultra-high compactness. The size of the whole machine is only tens of millimeters, the thermal power is only tens of watts, and the output laser pulse width is about tens of nanoseconds, which is conducive to further single pulse energy enhancement based on solid amplifiers. The repetition frequency can reach several thousand hertz, and the line width reaches the Fourier transform limit. The whole machine adopts semiconductor technology to achieve ultra-high stability packaging, which can withstand high and low temperature cycles and vibration shocks, providing a near-infrared single longitudinal mode pulse pump source with ultra-high reliability and ultra-compactness for mid-infrared optical parametric oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0013] Reference numerals:

[0014] 1. The first diode single tube; 2. The first fast axis collimating lens; 3. The first shaping lens; 4. The first resonant cavity reflector; 5. Passive Q-switched crystal; 6. The third resonant cavity reflector; 7. λ / 2 wave plate; 8. Faraday rotator; 9. Thin film polarizer; 10. Laser crystal; 11. The second resonant cavity reflector; 12. The second shaping lens; 13. The second fast axis collimating lens; 14. The second diode single tube; 15. Gold-plated sealed shell; 16. The first gold-plated ceramic; 17. The first semiconductor refrigerator; 18. The second gold-plated ceramic; 19. The third gold-plated ceramic; 20. The fourth gold-plated ceramic; 21. The first mounting screw; 22. The second mounting screw; 23. The first thermal insulation gasket; 24. The second thermal insulation gasket; 25. Heat dissipation fins; 26. The second semiconductor refrigerator. DETAILED DESCRIPTION

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

[0016] like Figure 1 As shown in the figure, it is a structure diagram of an air-cooled micro single-frequency laser based on a ring cavity of the present invention. The first diode single tube 1 and the second diode single tube 14 are 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 light-emitting area size is 200μm in the slow axis direction, 1μm in the fast axis direction, the spectrum half width full height ≤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 / ℃. The first light source passes through the second A fast axis collimating lens 2, a first shaping lens 3, and a first resonant cavity reflector 4 reach the laser crystal 10, and a second light source passes through a second fast axis collimating lens 13, a second shaping lens 12, and a second resonant cavity reflector 11 to reach the laser crystal 10, and a λ / 2 wave plate 7, a Faraday rotator 8, and a thin film polarizer 9 together constitute an optical diode, and the optical diode together with the first resonant cavity reflector 4, the second resonant cavity reflector 11, and the third resonant cavity reflector 6 constitute a ring resonant cavity, so that the laser light source reaching the laser crystal 10 oscillates in the ring resonant cavity. In particular, the first resonant cavity reflector 4, the second resonant cavity reflector 11, the third resonant cavity reflector 6, and the thin film polarizer 9 are all incident and emitted at 45 degrees to form a complete ring resonant cavity.

[0017] The first fast-axis collimating lens 2 and the second fast-axis collimating lens 13 respectively compress the fast-axis direction angle of the lasers emitted by the first diode single tube 1 and the second diode single tube 14. The first diode single tube 1 and the second diode single tube 14 are packaged in 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 diode single tube 1 and the second diode single tube 14. The other ends of the first diode single tube 1 and the second diode single tube 14 are bonded to the first gold-plated ceramic 16 to achieve high-reliability compression collimation of the divergence angle in the fast-axis direction. Since the distance between the two is very sensitive, online measurement and bonding are often performed based on precision control.

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

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

[0020] The passive Q-switched crystal 5 realizes compact Q-switching and achieves high-peak power pulsed laser oscillation and output. Since the pumping mechanism of the first diode single tube 1 and the second diode single tube 14 is continuous pumping, the particle number inversion density increases exponentially from zero during the energy storage stage. After meeting the laser oscillation threshold corresponding to the small signal transmittance of the passive Q-switched crystal 5, the particle number inversion density is converted into laser output, and the laser begins to oscillate, achieving tens of nanoseconds of laser output. The particle number inversion density remains slightly, and the exponential gain process is repeated again to prepare for the next energy extraction process.

[0021] The λ / 2 wave plate 7, the Faraday rotator 8 and the thin-film polarizer 9 together constitute an optical diode, so that the laser oscillates only counterclockwise. At the same time, the angle of the λ / 2 wave plate 7 is adjusted so that 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, maintaining the power density in the resonant cavity at a reasonable value, avoiding damage to optical components, and is easy to calculate based on the Jones matrix.

[0022] The laser crystal 10 adopts a double-diode single-tube double-end pumping structure, the thermal effect is symmetrical at both ends, the laser oscillation gain of the ring resonator is relatively uniform, the polarization loss and spatial hole burning effect caused by thermally induced birefringence are eliminated, and it is helpful to achieve single-frequency laser oscillation.

[0023] like Figure 2 The figure shows a schematic diagram of the packaging structure of an air-cooled miniature single-frequency laser based on a ring cavity of the present invention. In order to avoid the resonant cavity mode jumping, the laser whole machine packaging adopts an ultra-high stability semiconductor packaging process.

[0024] Among them, the first diode single tube 1 and the second diode single tube 14 are gold-plated and welded to the upper end surface of the first gold-plated ceramic 16 respectively. The lower end surface of the first gold-plated ceramic 16 achieves ultra-high temperature control of ±0.01°C based on the first semiconductor refrigerator 17. The mechanical stability and temperature stability ensure that the pump source is almost unchanged.

[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 surface of the fourth gold-plated ceramic 20.

[0026] To further improve the temperature stability, the entire laser is sealed in a 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 entire laser performs secondary semiconductor refrigerator temperature control. The gold-plated sealed housing 15 uses a first thermal insulation gasket 23 and a second thermal insulation gasket 24, and is installed on the second semiconductor refrigerator 26 and the heat sink fins 25 stacked on top of each other in conjunction with the first mounting screws 21 and the second mounting screws 22. Due to the low thermal power, an air-cooled heat dissipation design can be fully adopted, and the thermal power of the entire machine is dissipated by the heat sink fins 25. Based on the above packaging process, ultra-stable and reliable packaging can be achieved.

[0027] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An air-cooled miniature single-frequency laser based on a ring cavity, characterized in that: It includes a first diode single tube, a first fast axis collimating lens, a first shaping lens, a first resonant cavity reflector, a third resonant cavity reflector, a λ / 2 wave plate, a Faraday rotator, a thin film polarizer, a laser crystal, a second resonant cavity reflector, a second shaping lens, a second fast axis collimating lens, and a second diode single tube, wherein: The first diode single tube and the second diode single tube are arranged on both sides of the laser crystal to generate two light sources, wherein the first light source passes through the first fast axis collimating lens, the first shaping lens, and the first resonant cavity reflector 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 reflector to reach the laser crystal; 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 reflector, the second resonant cavity reflector and the third resonant cavity reflector together constitute a ring resonant cavity, so that the laser light source reaching the laser crystal oscillates in the ring resonant cavity and then is output through the thin-film polarizer.

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

3. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 2, characterized in that: The first resonant cavity reflector, the second resonant cavity reflector, the third resonant cavity reflector, and the thin film polarizer are all incident and emitted at 45 degrees.

4. The air-cooled miniature 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 respectively perform fast-axis angle compression on the lasers emitted by the first diode and the second diode.

5. The air-cooled miniature 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 laser light after angle compression respectively.

6. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 1, characterized in that: The first resonant cavity reflector and the second resonant cavity reflector are used to respectively receive two focused light sources to achieve round-trip gain reflection of the oscillating laser, and the coating is highly reflective of the oscillating laser.

7. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 1, characterized in that: A passive Q-switched crystal is also included between the first resonant cavity reflector and the third resonant cavity reflector, which is used to achieve compact Q-switching, high peak power pulse laser oscillation and output.

8. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 1, characterized in that: The laser light source oscillates only counterclockwise in the ring resonant cavity.

9. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 1, characterized in that: The λ / 2 wave plate angle is adjusted to change the output laser ratio when the oscillating laser is reflected by the thin film polarizer.

10. The air-cooled miniature single-frequency laser based on a ring cavity according to claim 1, characterized in that: The first diode single tube and the second diode single tube are respectively welded to the upper end surface of the first gold-plated ceramic by gold plating, and the lower end surface of the first gold-plated ceramic is connected to the upper end surface 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 surface 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 surface of the fourth gold-plated ceramic; then the entire laser is sealed in a gold-plated sealed housing.

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