Air-cooled miniature slab laser based on double-end pumping

Abstract

The invention discloses an air-cooled miniature slab laser based on double-end pumping, and belongs to the technical field of solid laser. Wherein the first conduction cooling single bar and the second conduction cooling single bar are arranged at the upper end and the lower end of the lath laser crystal in a staggered manner to form a double-end pumping structure; after the first fast axis collimation cylindrical lens and the second fast axis collimation cylindrical lens respectively collimate the fast axis directions of the first conduction cooling single bar and the second conduction cooling single bar, partial end surfaces are injected into the lath laser crystal; the first resonant cavity reflector and the second resonant cavity reflector are located at the left end and the right end of the lath laser crystal; the laser injected into the slab laser crystal passes through the resonant cavity mirror and then is subjected to multi-pass back-and-forth oscillation between the first resonant cavity reflector and the second resonant cavity reflector to reach the resonant cavity output cavity mirror. The output monopulse energy is greatly improved, the overall electro-optical efficiency is high, and the system compactness is high.

Description

Technical Field

[0001] The invention belongs to the technical field of solid lasers, and in particular relates to an air-cooled micro-slab laser based on double-end pumping. Background Art

[0002] Atmospheric detection lidar uses the interaction between laser and atmospheric components to obtain backscattered echo signals, which can detect atmospheric aerosol concentration, measure gas, atmospheric temperature and humidity and other parameters. Among them, laser is a key component. Existing miniature air-cooled lasers are often based on the following forms: first, the fiber coupling module directly pumps the rod-shaped crystal, which is limited by the fiber bending radius and fiber pigtail, and the compactness cannot meet the requirements; second, the rod-shaped side pump, the single pulse energy output is high, the thermal effect is more serious, the output beam quality is often poor, and it cannot meet the miniature requirements; third, the diode single tube directly pumps the rod-shaped crystal, which can meet the miniaturization requirements, but is limited by the cavity mode volume size, and the output single pulse is often low; fourth, it is based on the Zigzag slab gain medium, the single pulse energy output is high, but limited by the inherent design, the beam quality factor often cannot reach the diffraction limit.

[0003] Diode single-tube pumped rod-shaped laser crystals, called microchip lasers, have low single-pulse energy output, but are compact in overall size, stable and reliable in performance, and relatively low in cost. They are only used in atmospheric detection fields where single-pulse energy requirements are not high, such as ceilometers. In order to meet the large single-pulse energy requirements, cascade amplifiers are often required for energy amplification. However, since the diode single-tube pump power is often only about 10W, the microchip laser resonant cavity length is short and cannot reach the oscillation threshold. The laser pulse width is often sub-nanosecond or even hundreds of picoseconds. The narrower the pulse width, the higher the peak power density. The damage threshold of optical components becomes the main limitation of single-pulse amplification. In order to obtain a larger single-pulse energy, the spot size often needs to be very large, which means that the spatial volume is very poorly compact and the microchip laser characteristics are completely obscured. For single-frequency atmospheric detection lidar, the wider the pulse width, the narrower the Fourier limit linewidth, and the pulse width is often required to reach 30ns. The actual laser linewidth is less than 50MHz, which means that the sub-nanosecond or even hundreds of picosecond laser pulse widths of conventional microchip lasers cannot meet the needs of single-frequency atmospheric detection lidar. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an air-cooled micro-slab laser based on double-end pumping, which simultaneously meets the requirements of high beam quality, large single pulse energy, compact system size, high reliability and high environmental adaptability.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A double-ended pumped air-cooled micro-slab laser comprises a resonant cavity mirror, a first resonant cavity reflector, a slab laser crystal, a first conduction-cooled diode single bar, a first fast-axis collimating cylindrical lens, a second resonant cavity reflector, a thin-film polarizer, a passive Q-switching switch, a resonant cavity output cavity mirror, a second fast-axis collimating cylindrical lens, and a second conduction-cooled diode single bar, wherein:

[0007] The first conduction-cooled single bar and the second conduction-cooled single bar are alternately placed at the upper and lower ends of the slab laser crystal, presenting a double-end pumping structure;

[0008] The first fast-axis collimating cylindrical lens and the second fast-axis collimating cylindrical lens collimate the fast-axis directions of the first conductively cooled single-bar strip and the second conductively cooled single-bar strip respectively, and then partially inject the end faces into the slab laser crystal;

[0009] The first resonant cavity reflector and the second resonant cavity reflector are located at the left and right ends of the slab laser crystal; the laser light injected into the slab laser crystal passes through the resonant cavity mirror and then performs a multi-pass back-and-forth oscillation between the first resonant cavity reflector and the second resonant cavity reflector to reach the resonant cavity output cavity mirror;

[0010] The thin film polarizer and the passive Q-switching switch are located at the front end of the resonant cavity output cavity mirror and are used to realize linear polarization pulse laser output.

[0011] The beneficial effects of the present invention are:

[0012] The present invention comprehensively inherits the excellent characteristics of microchip lasers, such as high beam quality, compact system size, high reliability and high environmental adaptability, while obtaining large single pulse energy and relatively wide laser pulse width. The conduction-cooled single bar means that the laser does not need liquid cooling, and air cooling can be achieved. The pump structure is a double-ended pump structure, and the pump source has no crosstalk, which improves the system reliability. The pump power is greatly improved, but the thermal effect does not increase synchronously. The temperature field of the slab laser crystal is almost a one-dimensional temperature field, and the laser output maintains a near-diffraction-limited output. The multi-pass round-trip oscillation laser fully extracts all the pump power, and the multi-pass round-trip indirectly increases the resonant cavity length and cavity mode size, and the output single pulse energy is greatly improved. The overall electro-optical efficiency is high, and the passive Q-switched crystal does not require external high voltage and no additional electronic devices, and the system compactness is further enhanced. The laser is packaged based on a semiconductor packaging process to achieve high reliability and high environmental adaptability. On the other hand, the present invention does not limit the laser wavelength band. In addition to the common 1 μm lasers such as 1064 nm / 1319 nm / 1047 nm, it can be easily expanded to the 1.5 μm / 2 μm band. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a structural diagram of an air-cooled micro-slab laser based on double-end pumping according to the present invention.

[0014] Reference numerals:

[0015] 1. Resonant cavity mirror; 2. First resonant cavity reflector; 3. Slab laser crystal; 4. First conduction-cooled diode single bar; 5. First fast-axis collimating cylindrical lens; 6. Second resonant cavity reflector; 7. Thin-film polarizer; 8. Passive Q-switching switch; 9. Resonant cavity output cavity mirror; 10. Second fast-axis collimating cylindrical lens; 11. Second conduction-cooled diode single bar. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0017] The invention provides an air-cooled micro-slab laser based on double-end pumping. The pump source is a conduction-cooled single bar, the pump structure is a double-end pumping structure, the pump power is increased by 30 times relative to a diode single tube, the laser crystal adopts a slab laser crystal, the pump power is increased while the thermal effect does not increase synchronously, the slab laser crystal is nearly flat-top distributed in the width direction, the temperature field is nearly a one-dimensional temperature field, the laser output still maintains a near-diffraction-limited output, the multi-pass round-trip oscillation laser spot is elliptical, and circular symmetry is performed after output, the elliptical oscillation laser passes through the slab laser crystal for multiple round trips, all the pump power is fully extracted, the overall electro-optical efficiency is very high, the Q-switching switch adopts a passive Q-switching crystal to further improve the compactness of the system, the laser as a whole is packaged in a gold-plated shell based on a semiconductor packaging process, and high reliability and high environmental adaptability are achieved.

[0018] like Figure 1 As shown, the pump source is a first conduction-cooled single bar 4 and a second conduction-cooled single bar 11, which are placed alternately to present a double-end pump structure. The first fast-axis collimating cylindrical lens 5 and the second fast-axis collimating cylindrical lens 10 collimate the fast-axis directions of the first conduction-cooled single bar 4 and the second conduction-cooled single bar 11 respectively. The pump spot is distributed in a flat-top manner in the slow-axis direction, and part of the end face is injected into the slab laser crystal 3. The temperature field of the slab laser crystal 3 is almost a one-dimensional temperature field. The resonant cavity mirror 1, the first resonant cavity reflector 2, the second resonant cavity reflector 6 and the resonant cavity output cavity mirror 9 together constitute a laser resonant cavity. The multi-pass reciprocating oscillation laser spot is elliptical, and the beam quality is close to the diffraction limit. The resonant cavity as a whole is a multi-pass reciprocating structure, which can fully extract all pump powers and has high overall electro-optical efficiency. The thin-film polarizer 7 and the passive Q-switch 8 realize linearly polarized pulse laser output, and the system is highly compact. The laser as a whole is packaged in a gold-plated shell based on the semiconductor packaging process, and the whole machine can achieve high reliability and high environmental adaptability.

[0019] The resonant cavity mirror 1 is a high-reflector of the oscillating laser, and is used to feedback gain to amplify the oscillating laser;

[0020] The first resonant cavity reflector 2 and the second resonant cavity reflector 6 are located on both sides of the slab laser crystal 3, so that the oscillating laser makes multiple round trips, and the coating is highly reflective of the oscillating laser;

[0021] The slab laser crystal 3 is very thin in thickness direction and acts as an aperture stop, so that the received oscillating laser only oscillates in the fundamental mode, ensuring that the output laser is diffraction-limited. At the same time, the two larger surfaces are frosted and welded to the heat sink for efficient heat dissipation. Since the thermal lens only exists in the thickness direction, the oscillating laser in the resonant cavity is elliptical, and multiple round trips fully cover the gain area to extract all pump energy;

[0022] The first conductive cooling diode bar 4 and the second conductive cooling diode bar 11 are based on semiconductor technology to realize the horizontal arrangement of multiple groups of diode single tubes. The pump power is increased by dozens of times compared with the diode single tube. The width dimension is about half of the width of the slab laser crystal 3. The first conductive cooling diode bar 4 and the second conductive cooling diode bar 11 are staggered and pumped oppositely. The pump residue will not affect the opposite diode bar and thus affect the stability and reliability of the pump source. The divergence angle in the fast axis direction is compressed based on the first fast axis collimating cylindrical lens 5 and the second fast axis collimating cylindrical lens 10. The first fast axis collimating cylindrical lens 5 and the second fast axis collimating cylindrical lens 10 are aspherical structures and the focal length is less than 1 mm. The requirement for installation and adjustment accuracy is extremely high. After the fast-axis collimation of the first conduction-cooled diode single bar 4 and the second conduction-cooled diode single bar 11, the diode single bar beam size is rectangular, less than 1mm in the fast-axis direction, and about 10mm in the slow-axis direction. It is directly injected into the pump slab laser crystal 3. The pump and slab laser crystal sizes are perfectly matched, and the pump structure is a double-ended pump structure. Since the diode single bar is a conduction-cooled structure, the overall volume size is only tens of millimeters. At the same time, the resonant cavity adopts a multi-pass folding structure and uses pulse pumping. The extremely low thermal power consumption can be directly transmitted to the installation surface. The laser as a whole can efficiently dissipate heat based on air cooling, and the overall microstructure of the laser can achieve a large single pulse energy output.

[0023] The thin film polarizer 7 makes the oscillating laser a polarized laser with a transmission angle of 45°. The coating is highly transparent to the oscillating-level light. The slab laser crystal 3 acts as a gain medium to generate spontaneous radiation laser oscillation. Only horizontally polarized light is allowed to oscillate when transmitted to the thin film polarizer 7. During the laser oscillation process, the passive Q-switching switch 8 is gradually bleached, and the oscillating laser is quickly output by the resonant cavity output mirror 9 to form a high-energy nanosecond pulse laser output.

[0024] Passive Q-switching switch 8 often uses Cr4+:YAG. The pump threshold, output single pulse energy, resonant cavity output mirror reflectivity and small signal transmittance of passive Q-switching switch 8 are closely related. If the small signal transmittance is too high, the pump threshold will be too small, the output single pulse energy will be low, and multiple pulses will be easily generated. If the small signal transmittance is too low, the pump threshold will be too high. In order to ensure the effective energy storage of slab laser crystal 3 in the energy storage stage, once the passive Q-switching switch 8 reaches bleaching, the resonant cavity oscillation photons are stimulated and amplified, and laser pulse oscillation is quickly formed. Part of the energy is output by the resonant cavity output mirror 9.

[0025] The reflectivity of the coating on the resonant cavity output mirror 9 determines the output ratio of the oscillating laser. Too low a reflectivity will lead to unstable oscillating laser, while too high a reflectivity will lead to too few output photons. The power density in the resonant cavity is too high, which can easily damage the optical components in the resonant cavity. The reflectivity can be theoretically evaluated based on the laser dynamics equation.

[0026] 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 protection scope of the present invention.

Claims

1. An air-cooled micro-slab laser based on double-end pumping, characterized in that: It includes a resonant cavity mirror, a first resonant cavity reflector, a slab laser crystal, a first conduction-cooled diode single bar, a first fast-axis collimating cylindrical lens, a second resonant cavity reflector, a thin-film polarizer, a passive Q-switching switch, a resonant cavity output cavity mirror, a second fast-axis collimating cylindrical lens, and a second conduction-cooled diode single bar, wherein: The first conduction-cooled single bar and the second conduction-cooled single bar are alternately placed at the upper and lower ends of the slab laser crystal, presenting a double-end pumping structure; The first fast-axis collimating cylindrical lens and the second fast-axis collimating cylindrical lens collimate the fast-axis directions of the first conductively cooled single-bar strip and the second conductively cooled single-bar strip respectively, and then partially inject the end faces into the slab laser crystal; The first resonant cavity reflector and the second resonant cavity reflector are located at the left and right ends of the slab laser crystal; the laser light injected into the slab laser crystal passes through the resonant cavity mirror and then performs a multi-pass back-and-forth oscillation between the first resonant cavity reflector and the second resonant cavity reflector to reach the resonant cavity output cavity mirror; The thin film polarizer and the passive Q-switching switch are located at the front end of the resonant cavity output cavity mirror and are used to realize linear polarization pulse laser output.

2. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The resonant cavity mirror is highly reflective of the oscillating laser and is used for feedback gain amplification of the oscillating laser.

3. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The coatings of the first resonant cavity reflector and the second resonant cavity reflector are highly reflective of oscillating laser.

4. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The slab laser crystal also plays the role of an aperture stop, so that the received oscillation laser only oscillates in the fundamental mode and the output laser is diffraction-limited.

5. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The resonant cavity mirror, the first resonant cavity reflector, the second resonant cavity reflector and the resonant cavity output cavity mirror together constitute a laser resonant cavity, and the oscillating laser in the resonant cavity is elliptical.

6. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The first conductive cooling diode bar and the second conductive cooling diode bar realize horizontal arrangement of multiple groups of diode single tubes based on semiconductor technology, and the first conductive cooling diode bar and the second conductive cooling diode bar are alternately pumped in opposite directions.

7. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The width dimensions of the first conductive cooling diode single bar and the second conductive cooling diode single bar are half of the width of the slab laser crystal.

8. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The first fast-axis collimating cylindrical lens and the second fast-axis collimating cylindrical lens are aspherical structures and have focal lengths less than 1 mm. After fast-axis collimation of the first conductively cooled diode single-bar and the second conductively cooled diode single-bar, the diode single-bar beam size is rectangular and is directly injected into the pump slab laser crystal.

9. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The thin film polarizer makes the oscillating laser polarized laser with a transmission angle of 45°. The coating is highly transparent to the oscillation-level light. During the laser oscillation process, the passive Q-switching switch is gradually bleached, and the oscillating laser is quickly output from the resonant cavity output mirror.

10. The air-cooled micro-slab laser based on double-end pumping according to claim 1, characterized in that: The reflectivity of the coating on the resonant cavity output mirror determines the oscillation laser output ratio.

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