CN102969648A - High-power intermediate infrared laser device based on intra-cavity frequency conversion - Google Patents

Abstract

The invention discloses a high-power mid-infrared laser based on intracavity frequency conversion, which is characterized in that it comprises: a semiconductor laser pump module arranged in sequence along the laser transmission direction, an optical coupling system, a fundamental frequency laser crystal, and a mid-infrared laser reflector A mirror, a mid-infrared nonlinear crystal, a laser resonator for forming a high-beam fundamental-frequency beam from the light emitted by the aforementioned fundamental-frequency laser crystal, and a modulation device for modulating the aforementioned high-beam fundamental-frequency beam. The advantages of the present invention are: compact structure and good stability; the process of converting the mid-infrared laser from 1064nm laser to 3.8μm laser is completed outside the cavity to be completed inside the cavity, using the high power density in the 1064nm cavity, The wavelength conversion efficiency is greatly improved, thereby obtaining a mid-infrared laser output with high conversion power.

Description

High-power mid-infrared laser based on intracavity frequency conversion

technical field

The invention belongs to the field of optical-mechanical-electrical integration, and in particular relates to a high-power mid-infrared laser based on intracavity frequency conversion.

Background technique

End-pumped lasers are popular because of their simple device, sufficient absorption of pump light by fundamental-frequency laser crystals, good output beam quality, and high efficiency.

Lasers located in the 2-5 μm mid-infrared band have special and important applications in national defense, medical treatment, and communications. It is located in the "transparent window" of the atmosphere and is in the working band of most military detectors. It can be used for military purposes such as tactical missile tail flame infrared radiation simulation, eye-safe laser radar, and laser directional infrared interference. In the civil field, it can be used for remote sensing chemical sensing and air pollution control. It can also be used in a new generation of laser surgery to coagulate blood quickly, with small surgical wounds and good hemostasis (water molecules have a strong absorption peak near 3 μm). In addition, it is also a topic of great research value to use 2-5 μm to replace the widely used 1.55 μm as the working wavelength of optical fiber communication. Since the Rayleigh scattering of materials is inversely proportional to the fourth power of the light wavelength, 2-5 μm is used as the wavelength. The working wavelength can effectively reduce fiber loss and increase the distance of non-relay communication. Therefore, the research and development of lasers in the mid-infrared band is of great significance to national security and national economic construction.

Contents of the invention

The purpose of the present invention is to provide a high-power mid-infrared laser based on intra-cavity frequency conversion that makes full use of the strong fundamental wave light in the cavity to obtain high efficiency and high beam quality.

In order to achieve the above object, the present invention adopts the following technical solutions:

A high-power mid-infrared laser based on intracavity frequency conversion, characterized in that it includes: a semiconductor laser pump module arranged in sequence along the laser transmission direction, an optical coupling system, a fundamental frequency laser crystal, a mid-infrared laser reflector, a mid-infrared A nonlinear crystal, a laser resonator for forming a high-beam fundamental-frequency beam from the light emitted by the aforementioned fundamental-frequency laser crystal, and a modulation device for modulating the aforementioned high-beam fundamental-frequency beam; the aforementioned optical coupling system is composed of lenses; the aforementioned The "C" axis of the fundamental frequency laser crystal is placed vertically or horizontally; the aforementioned laser resonator is composed of cavity mirrors.

The pump light output by the aforementioned semiconductor laser pumping module is transmitted to the optical coupling system, collimated and focused by the optical coupling system, and then coupled to the end face of the fundamental-frequency laser crystal. The fundamental-frequency laser crystal absorbs the energy of the pump light and generates stimulated emission. The emitted light forms a high-beam-quality fundamental frequency beam through the mode selection of the laser resonator mirror in the laser resonator, and under the modulation of the modulation device, a modulated laser with high peak power is obtained; the modulated fundamental frequency laser is injected into the center The optical parametric oscillation is amplified in the infrared nonlinear crystal to obtain the mid-infrared laser output.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the center wavelength of the aforementioned semiconductor laser pump module is 808nm or 880nm.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the aforementioned fundamental frequency laser crystal is Nd:YVO4, Nd:YLF, Nd:YAG, Nd:Glass, Yb:YAG or Er:YAG.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the end face of the aforementioned fundamental frequency laser crystal is coated with an anti-reflection coating for anti-reflection of pump light and 1064nm laser.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the aforementioned mid-infrared nonlinear crystal is phosphorus germanium zinc or PPLN artificial crystal.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the two ends of the aforementioned mid-infrared nonlinear crystal are coated with three-color high-transparency films of 1064 nm, 1.4 μm and 3.8 μm.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the structure of the aforementioned laser resonator is a Z-shaped cavity, a V-shaped cavity or other angle-folded cavity structures.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the cavity mirror of the aforementioned laser resonator is a plane mirror or a concave mirror or a combination of both.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the aforementioned modulation device is an acousto-optic modulation device, an electro-optic modulation device or an absorption passive Q-switching switch.

The aforementioned high-power mid-infrared laser based on intracavity frequency conversion is characterized in that the laser output end in the aforementioned laser resonator is provided with an intracavity lens or lens group.

The advantages of the present invention are: compact structure and good stability; the process of converting the mid-infrared laser from 1064nm laser to 3.8μm laser is completed outside the cavity to be completed inside the cavity, using the high power density in the 1064nm cavity, The wavelength conversion efficiency is greatly improved, so that the mid-infrared laser output with high conversion power can be obtained; without changing the internal structure of the laser, within the range of the damage value of the fundamental frequency laser crystal, the pumping power of the semiconductor laser pump module can be increased , to further increase the power density of the fundamental frequency laser in the cavity, so as to obtain a higher power mid-infrared laser output.

Description of drawings

Fig. 1 is a schematic structural view of a specific embodiment of a high-power mid-infrared laser based on intracavity frequency conversion of the present invention;

Fig. 2 is the laser output spectrum test result figure in Fig. 1;

Fig. 3 is the laser power stability test result diagram in Fig. 1;

Fig. 4 is a graph showing the relationship between laser current and output power in Fig. 1;

The meanings of reference signs in the figure: 1-semiconductor laser pump module, 2-lens, 3-lens, 4-cavity mirror, 5-fundamental frequency laser crystal, 6-cavity mirror, 7-cavity mirror, 8-modulation device , 9-cavity mirror, 10-cavity mirror, 11-cavity mirror, 12-cavity mirror, 13-cavity lens, 14-mid-infrared laser mirror, 15-mid-infrared nonlinear crystal, 16-cavity mirror.

Detailed ways

The present invention will be specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

Referring to Fig. 1, the high-power mid-infrared laser based on intracavity frequency conversion of the present invention includes: a semiconductor laser pump module 1, an optical coupling system, a fundamental frequency laser crystal 5, and a mid-infrared laser mirror 14 arranged in sequence along the laser transmission direction , a mid-infrared nonlinear crystal 15, a laser cavity for forming a high-beam fundamental-frequency beam from the light emitted by the fundamental-frequency laser crystal 5, and a modulation device 8 for modulating the high-beam fundamental-frequency beam. Among them, the optical coupling system is composed of lenses, specifically including lens 2 and lens 3; the "C" axis of the fundamental frequency laser crystal 5 is placed vertically, which can ensure that the polarization direction of the fundamental frequency laser generated by it is vertical, and the "C" axis is also It can be rotated 90 degrees, that is, placed horizontally. Correspondingly, the direction of the mid-infrared nonlinear crystal 15 is also rotated 90 degrees; the laser resonator is composed of cavity mirrors, specifically including cavity mirrors 4, 6, 7, 9, 10, 11, and 12 , 16, wherein the cavity mirrors 4, 6, 7, 10, 11, 12 are placed at an angle of 45 degrees or 135 degrees to the horizontal direction, and the cavity mirrors 9, 16 are placed vertically.

The laser of the present invention also includes an optical fiber (not shown) that transmits the pump light output by the semiconductor laser pump module 1 to the optical coupling system, and can also transmit the pump light output by the semiconductor laser pump module 1 without passing through the optical fiber. Direct transmission to the optical coupling system.

Referring to Fig. 1, the working principle of the laser of the present invention is: the pumping light output by the semiconductor laser pumping module 1 is transmitted to the optical coupling system, and is coupled to the end face of the fundamental frequency laser crystal 5 after being collimated and focused by the optical coupling system. The high-frequency laser crystal 5 absorbs the energy of the pump light to produce stimulated emission, and the emitted light forms a high-beam-quality fundamental-frequency beam in the laser resonator through the mode selection of the laser resonator mirror. Under the modulation of the modulation device 8, A modulated laser with high peak power is obtained; the modulated fundamental-frequency laser is injected into the mid-infrared nonlinear crystal 15 for optical parametric oscillation amplification, and a mid-infrared laser output is obtained.

As a preferred solution, the laser output end in the laser resonator cavity is provided with an intracavity lens 13 or a lens group composed of several intracavity lenses 13 . The intracavity lens 13 is a convex lens coated with a high-transparency film for 1064nm laser. Because it has a converging effect, after the fundamental frequency laser is converged, a smaller spot and a larger power can be obtained inside the mid-infrared nonlinear crystal 15. density.

In the present invention, the semiconductor laser pumping module 1 is a semiconductor laser diode with a central wavelength of 808nm and a maximum output power of 30W. It is also possible to select semiconductor laser diodes with other central wavelengths according to the selected fundamental frequency laser crystal 5 , for example, select a semiconductor laser diode with a central wavelength of 880 nm.

In the present invention, the fundamental frequency laser crystal 5 is Nd:YVO4, which can also be Nd:YLF, Nd:YAG, Nd:Glass, Yb:YAG or Er:YAG. As a preferred solution, the end face of the fundamental frequency laser crystal 5 is coated with an anti-reflection coating for pumping light and 1064nm laser to increase its absorption of pumping light.

In the present invention, the mid-infrared laser reflector 14 is a plane mirror, coated with a high-transparency film for 1064nm laser, and a high-reflection film for 1.4 μm and 3.8 μm laser.

In the present invention, the mid-infrared nonlinear crystal 15 is phosphorous germanium zinc, and it can also be a PPLN artificial crystal.

As a preferred solution, both ends of the mid-infrared nonlinear crystal 15 are coated with three-color high-transparency films of 1064 nm, 1.4 μm and 3.8 μm.

As a preferred solution, both the fundamental-frequency laser crystal 5 and the mid-infrared nonlinear crystal 15 are wrapped with indium foil and placed in a heat-dissipating crystal seat.

The following describes the laser resonator.

The laser resonator is used to form a high-beam fundamental-frequency beam from the light emitted by the fundamental-frequency laser crystal 5 . Among them, the cavity mirror 4 is set on the front end of the fundamental frequency laser crystal 5, which is at an angle of 45 degrees to the horizontal direction, and its end face is coated with a high-transparency film for pump light and a high-reflection film for 1064nm laser; the cavity mirrors 6 and 7 are set on the base Between the frequency laser crystal 5 and the modulation device 8, the angles to the horizontal direction are 45 degrees and 135 degrees respectively, and the end faces are coated with a high reflection film for 1064nm laser; cavity mirrors 10, 11, 12 are arranged between the base frequency laser crystal 5 and the Between the intracavity lenses 13, angles of 135 degrees, 45 degrees, and 45 degrees are respectively formed with the horizontal direction, and the end faces are coated with a high-reflection film for 1064nm laser; , the end surface is coated with a high reflection film for 1064nm laser; the cavity mirror 16 is placed vertically and set at the tail end of the mid-infrared nonlinear crystal 15, and its end surface is coated with a high reflection film for 1064nm and 1.4μm laser, and a high transparency for 3.8μm laser membrane.

The cavity mirrors 4, 6, 7, 9, 10, 11, 12, and 16 can all be plane mirrors, also can all be concave mirrors, or can be a combination of plane mirrors and concave mirrors.

As a preferred solution, the cavity mirrors 4, 6, 7, 9, 10, 11, 12, and 16 are all plane mirrors.

As a preferred solution, the structure of the laser resonant cavity of the laser of the present invention is a Z-shaped cavity, a V-shaped cavity or other angle-folded cavity structures.

The typical output wavelength of the laser of the present invention includes the mid-infrared band of 1.3-5 μm, not limited to 3.8 μm, and the output wavelength is specifically determined by the phase matching condition of the mid-infrared nonlinear crystal 15 .

With the laser of the present invention, without changing the internal structure of the laser, within the range of the fundamental frequency laser crystal destruction threshold, the pumping power of the laser diode can be increased, and the power density of the fundamental frequency laser in the cavity can be further increased, thereby obtaining Higher power mid-infrared laser output.

Referring to Figures 2 to 4, the high-power mid-infrared laser based on intracavity frequency conversion established according to the above technical scheme was tested. The test results are as follows: the measured laser wavelength is 3.843 μm; when the laser pulse power is 40khz, at 30W , 808nm optical pump power, the maximum output power of 3.8μm reaches 2.3W; in the continuous one-hour test process, the minimum power of the laser is 2.12W, the maximum power is 2.22W, the average power is 2.18W, and the long-term stability is 4.6 %. It can be seen that the laser device of the present invention has the advantages of compact structure, high conversion efficiency, good stability and the like.

It should be noted that the above embodiments do not limit the present invention in any form, and all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (10)

1. A high-power mid-infrared laser based on intracavity frequency conversion, characterized in that it includes: a semiconductor laser pump module, an optical coupling system, a fundamental frequency laser crystal, a mid-infrared laser reflector, and a mid-infrared A nonlinear crystal, a laser resonator for forming a high-beam fundamental-frequency beam from the light emitted by the above-mentioned fundamental-frequency laser crystal, and a modulation device for modulating the above-mentioned high-beam fundamental-frequency beam; the above-mentioned optical coupling system is composed of lenses; the above-mentioned The "C" axis of the fundamental frequency laser crystal is placed vertically or horizontally; the above-mentioned laser resonant cavity is composed of a cavity mirror. 2. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 1, wherein the central wavelength of the semiconductor laser pump module is 808nm or 880nm. 3. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 1, wherein the above-mentioned fundamental frequency laser crystal is Nd:YVO , Nd:YLF, Nd:YAG, Nd:Glass, Yb:YAG Or Er:YAG. 4. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 3, characterized in that the end face of the fundamental frequency laser crystal is coated with an anti-reflection coating for anti-reflection of pump light and 1064nm laser. 5. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 1, wherein the above-mentioned mid-infrared nonlinear crystal is phosphorus germanium zinc or PPLN artificial crystal. 6. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 5, wherein the two ends of the mid-infrared nonlinear crystal are coated with three-color high-transparency films of 1064 nm, 1.4 μm and 3.8 μm. 7. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 1, wherein the structure of the above-mentioned laser resonator is a Z-shaped cavity, a V-shaped cavity or other angle-folded cavity structures. 8. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 7, wherein the cavity mirror of the laser resonator is a plane mirror or a concave mirror or a combination of both. 9. The high-power mid-infrared laser based on intracavity frequency conversion according to claim 1, wherein the modulation device is an acousto-optic modulation device, an electro-optic modulation device or an absorbing passive Q-switch. 10. The high-power mid-infrared laser based on intracavity frequency conversion according to any one of claims 1 to 9, characterized in that, the laser output end in the laser resonator cavity is provided with an intracavity lens or lens group.

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