A composite cavity nonlinear laser frequency conversion device

Abstract

The present invention discloses a compound cavity non-linear laser frequency conversion device, which device includes a laser gain module, a first resonant cavity, a second resonant cavity and a non-linear crystal; the laser gain module is used for radiating a laser of a first wavelength and a laser of a second wavelength; the first resonant cavity is used for generating a first oscillating laser, the wavelength of the first oscillating laser is the first wavelength, and the first oscillating laser does not output from the first resonant cavity; the second resonant cavity is used for generating a second oscillating laser, injecting the second oscillating laser into the first resonant cavity, and the wavelength of the second oscillating laser is the second wavelength; the non-linear crystal is arranged in the first resonant cavity and is used for performing frequency conversion on the first oscillating laser and the second oscillating laser to generate a frequency-converted laser, and the frequency-converted laser is output from the first resonant cavity. The present invention combines the characteristics of intra-cavity frequency conversion and extra-cavity frequency conversion, is easy to achieve mode matching of the non-linear crystal, effectively improves the frequency conversion efficiency, and provides a new way for generating a frequency-converted laser with high power and high beam quality.

Description

Technical Field

[0001] The present invention relates to the field of laser technology. More specifically, it relates to a compound cavity non-linear laser frequency conversion device. Background Art

[0002] Laser sources are widely used in many fields such as science, economy, and military. With the development of society, the demand for lasers with special wavelengths is also increasing. In addition to exploring new laser working media, non-linear optical frequency conversion of optical materials is also an effective method to enrich laser wavelengths. In a non-linear crystal operating stably, multiple non-linear effects such as second harmonic generation, sum frequency generation, and difference frequency generation exist simultaneously. By replacing different filtering devices, laser outputs with different wavelengths can be obtained. According to the position of the non-linear crystal inside or outside the laser resonator, the frequency conversion method is divided into two types: intra-cavity frequency conversion and extra-cavity frequency conversion. Intra-cavity frequency conversion makes full use of the advantage of high laser power density inside the cavity and is easy to obtain high conversion efficiency and output power. However, since intra-cavity second harmonic generation is used to achieve frequency conversion of two-wavelength lasers, it is necessary to adjust the two laser beams to be collinear inside the cavity to achieve phase matching of the non-linear crystal, and the optical path debugging is relatively difficult. Extra-cavity frequency conversion is easy to obtain good beam quality, has a simple structure, and is easy to achieve phase matching of the non-linear crystal. However, due to the single-pass of the laser through the non-linear crystal, the frequency conversion efficiency is relatively low. Summary of the Invention

[0003] The present invention provides a compound cavity non-linear laser frequency conversion device to solve at least one of the problems existing in the prior art.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention provides a compound cavity non-linear laser frequency conversion device, which includes a laser gain module, a first resonator, a second resonator, and a non-linear crystal. The non-linear crystal is disposed in the first resonator;

[0006] The laser gain module is used for radiating a laser of a first wavelength and a laser of a second wavelength;

[0007] The first resonator is used for generating a first oscillating laser, the wavelength of the first oscillating laser is the first wavelength, and the first oscillating laser does not output from the first resonator;

[0008] The second resonator is used for generating a second oscillating laser, the wavelength of the second oscillating laser is the second wavelength, and injecting the second oscillating laser into the first resonator;

[0009] The non-linear crystal is used for frequency-converting the first oscillating laser and the second oscillating laser to generate a frequency-converted laser, and the frequency-converted laser is output from the first resonator.

[0010] Optionally, the first resonant cavity includes a first mirror, a first beam splitter, and a second beam splitter, the second resonant cavity includes a first mirror and a first output mirror, the laser gain module is disposed between the first mirror and the first beam splitter, and the nonlinear crystal is disposed between the first beam splitter and the second beam splitter;

[0011] The first mirror is configured to reflect the laser of the first wavelength and the laser of the second wavelength. The first beam splitter is configured to reflect the laser of the first wavelength to the second beam splitter and transmit it through the nonlinear crystal. The first beam splitter is further configured to transmit the laser of the second wavelength and output frequency-converted laser. The second beam splitter is configured to reflect the laser of the first wavelength back to the first beam splitter and the first mirror. The laser of the first wavelength oscillates in the first resonant cavity to generate first oscillating laser. The second beam splitter is further configured to transmit the second oscillating laser;

[0012] The first output mirror is configured to reflect the laser of the second wavelength back to the first beam splitter to generate second oscillating laser, transmit the second oscillating laser out of the second resonant cavity, and inject the second oscillating laser into the first resonant cavity through the second beam splitter.

[0013] Optionally, the device further includes a birefringent filter disposed between the laser gain module and the first mirror. The birefringent filter is placed in a Brewster angle manner and is configured to convert the laser of the first wavelength into the laser of the first wavelength in a horizontally polarized state and convert the laser of the second wavelength into the laser of the second wavelength in a horizontally polarized state;

[0014] The birefringent filter is further configured to adjust the intensities of the first oscillating laser and the second oscillating laser.

[0015] Optionally, the laser gain module includes a first laser gain module for outputting the laser of the first wavelength and a second laser gain module for outputting the laser of the second wavelength.

[0016] Optionally, the first resonant cavity includes a second mirror, a second beam splitter, and a third beam splitter, the second resonant cavity includes a third mirror and a second output mirror, the first laser gain module is disposed between the second mirror and the third beam splitter, the nonlinear crystal is disposed between the third beam splitter and the second beam splitter, and the second laser gain module is disposed between the third mirror and the second output mirror;

[0017] The second reflector is used to reflect the laser of the first wavelength. The third beam splitter is used to reflect the laser of the first wavelength to the second beam splitter and transmit it through the nonlinear crystal, and is also used to output frequency-converted laser. The second beam splitter is used to reflect the laser of the first wavelength back to the third beam splitter and the second reflector. The laser of the first wavelength oscillates in the first resonant cavity to generate the first oscillating laser.

[0018] The third reflector is used to reflect the laser of the second wavelength back to the second output mirror to generate the second oscillating laser. The second oscillating laser is output through the second output mirror. The second output mirror is also used to inject the second oscillating laser into the first resonant cavity through the second beam splitter.

[0019] Optionally, the device further includes a birefringent filter disposed between the first laser gain module and the second reflector. The birefringent filter is placed in the Brewster angle manner, and is used to convert the laser of the first wavelength into the laser of the first wavelength with a horizontal polarization state, and is also used to adjust the intensity of the first oscillating laser.

[0020] Optionally, the device further includes a shaping lens, which is used to shape the second oscillating laser output from the second resonant cavity, so that the second oscillating laser and the first oscillating laser achieve mode matching.

[0021] Optionally, the device further includes a fourth reflector, which is used to adjust the optical path of the second oscillating laser output from the second resonant cavity, so that the second oscillating laser injected into the first resonant cavity is collinear with the first oscillating laser.

[0022] Optionally, the device further includes a temperature adjustment module for adjusting the temperature of the nonlinear crystal.

[0023] Optionally, the laser gain module includes a laser gain medium and a pump source. The device further includes a cooling module for cooling the laser gain medium.

[0024] The beneficial effects of the present invention are as follows:

[0025] In the present invention, a composite cavity is formed by coupling the first resonant cavity and the second resonant cavity. The second oscillating laser output from the second resonant cavity is injected into the first resonant cavity. Through the nonlinear crystal, the first oscillating laser and the second oscillating laser are frequency-converted, and the frequency-converted laser is output to the outside of the first resonant cavity. The laser optical path of the present invention is easy to adjust. Combining the in-cavity frequency conversion of the first resonant cavity and the out-of-cavity frequency conversion of the second resonant cavity, it is easy to achieve the mode matching of the nonlinear crystal, effectively improving the frequency conversion efficiency and obtaining high-power and high-beam-quality frequency-converted laser. Description of the Drawings

[0026] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0027] Figure 1 Shows a Nd:YAG-based composite cavity non-linear frequency conversion laser device in the first embodiment of the present invention;

[0028] Figure 2 Shows a Nd:YAG and Nd:YVO4-based composite cavity non-linear frequency conversion laser device in the second embodiment of the present invention. Detailed implementation manners

[0029] To more clearly illustrate the present invention, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the specific content described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0030] The present invention provides a composite cavity non-linear laser frequency conversion device, which combines the advantages of high in-cavity frequency conversion efficiency and easy phase matching of out-of-cavity frequency conversion to obtain high-power and high-quality beam frequency conversion laser. The device includes a laser gain module, a first resonant cavity, a second resonant cavity, and a non-linear crystal, and the non-linear crystal is disposed inside the first resonant cavity.

[0031] The laser gain module is used to output laser of a first wavelength and laser of a second wavelength;

[0032] The laser gain module includes a laser gain medium and a pump source. The laser gain medium material can be a crystal or glass, and the laser gain medium can be the same medium or different media; the laser gain module can radiate laser of a first wavelength and laser of a second wavelength; the pumping method of the pump source can be side pumping and / or end pumping, and can also be continuous pumping or quasi-continuous pumping.

[0033] The first resonant cavity is used to generate a first oscillating laser, and the first oscillating laser does not output from the first resonant cavity. The wavelength of the first oscillating laser is the first wavelength; the second resonant cavity is used to generate a second oscillating laser, and the wavelength of the second oscillating laser is the second wavelength. The non-linear crystal frequency-converts the first oscillating laser and the second oscillating laser to generate frequency-converted laser, and the frequency-converted laser is output through the first resonant cavity.

[0034] Figure 1 For the Nd:YAG-based composite cavity non-linear frequency conversion laser device of the present invention, the first resonant cavity includes a first mirror 1, a first beam splitter 4, a second beam splitter 10, and a birefringent filter 2. The second resonant cavity includes a first mirror 1, a first output mirror 5, and a birefringent filter 2. The laser gain module 3 is disposed between the first mirror 1 and the first beam splitter 4, and the non-linear crystal 11 is disposed between the first beam splitter 4 and the second beam splitter 10;

[0035] The first reflector 1 is used to reflect the laser of the first wavelength and the laser of the second wavelength back to the laser gain module. The first beam splitter 4 is used to reflect the laser of the first wavelength to the nonlinear crystal and transmit the laser of the second wavelength to the first output mirror 5. The first beam splitter 4 is also used to output the frequency-converted laser. The second beam splitter 10 is used to reflect the laser of the first wavelength back to the nonlinear crystal to generate the first oscillating laser 1-1;

[0036] The first output mirror 5 is used to reflect part of the laser of the second wavelength back to the first reflector 1. The laser of the second wavelength oscillates in the second resonant cavity to generate the second oscillating laser 2-1. The first output mirror 5 is also used to transmit the second oscillating laser 2-1 out of the second resonant cavity. The second oscillating laser 2-1 is injected into the first resonant cavity through the second beam splitter 10;

[0037] The birefringent filter 2 is arranged between the laser gain module 3 and the first reflector 1. The birefringent filter 2 is placed in the Brewster angle mode and is used to convert the laser of the first wavelength into the laser of the first wavelength with a horizontal polarization state and convert the laser of the second wavelength into the laser of the second wavelength with a horizontal polarization state. The birefringent filter 2 is also used to adjust the intensities of the first polarized laser 1-1 and the second oscillating laser 2-1.

[0038] The device further includes a fourth reflector and a shaping lens. The fourth reflector can be a reflector group, and the reflector group includes a first highly reflective mirror 6 and a second highly reflective mirror 9. The first highly reflective mirror 6 is used to reflect the second oscillating laser 2-1 output from the second resonant cavity; the shaping lens can be a shaping lens group, and the shaping lens group includes a first lens 7 and a second lens 8. The first lens 7 and the second lens 8 are arranged between the first highly reflective mirror 6 and the second highly reflective mirror 9. The first lens 7 and the second lens 8 are used to shape the second oscillating laser 2-1. The second oscillating laser 2-1 reflected by the first highly reflective mirror 6 is shaped by the first lens 7 and the second lens 8. The shaped second oscillating laser 2-1 is reflected by the second highly reflective mirror 9 and injected into the first resonant cavity; the positions and angles of the first highly reflective mirror 6 and the second highly reflective mirror 9 are adjusted so that the first oscillating laser 1-1 is collinear with the shaped second oscillating laser 2-1 to achieve phase matching.

[0039] A temperature adjustment module for adjusting the temperature of the nonlinear crystal 11 is arranged inside the nonlinear crystal 11 to avoid the decrease in the laser output power and the laser beam quality caused by the non-uniform temperature field inside the nonlinear crystal 11; the laser gain module 3 includes a laser gain medium and a pump source, and further includes a cooling module for cooling the laser gain medium to avoid the decrease in the laser output power and the laser beam quality caused by the too high temperature inside the laser gain module.

[0040] The first reflecting mirror 1 is coated with a high-reflection film for the first oscillating laser 1-1 and the second oscillating laser 2-1; the first beam splitter 4 is coated with a high-reflection film for the first oscillating laser 1-1, and a high-transmittance film for the second oscillating laser 2-1 and the frequency-converted laser 3-1; the second beam splitter 10 is coated with a high-reflection film for the first oscillating laser 1-1 and the frequency-converted laser 3-1, and is also coated with a high-transmittance film for the second oscillating laser 2-1; the first output mirror 5 is coated with a high-transmittance film for the second oscillating laser 2-1; the first high-reflection mirror 6 is coated with a high-reflection film for the second oscillating laser 2-1; and the second high-reflection mirror 9 is coated with a high-reflection film for the second oscillating laser 2-1.

[0041] Figure 2 The invention relates to a composite cavity nonlinear frequency conversion laser device based on Nd:YAG and Nd:YVO4, comprising a first resonant cavity, a second resonant cavity, a laser gain module, a birefringent filter 2, and a nonlinear crystal 11. The laser gain module comprises a first laser gain module 18 for outputting laser light of a first wavelength and a second laser gain module 14 for outputting laser light of a second wavelength. The second laser gain module 14 generates laser light of a second wavelength in a horizontal polarization state.

[0042] The first resonant cavity includes a second reflector 15, a third beam splitter 17, a second beam splitter 10 and a birefringent filter 2. The second resonant cavity includes a third reflector 16 and a second output mirror 13. A first laser gain module 18 is disposed between the second reflector 15 and the third beam splitter 17. The nonlinear crystal 11 is disposed between the third beam splitter 17 and the second beam splitter 10. The second laser gain module 14 is disposed between the third reflector 16 and the second output mirror 13.

[0043] The second reflector 15 is used to reflect the laser light of the first wavelength to the third beam splitter 17. The third beam splitter 17 is used to reflect the laser light of the first wavelength to the second beam splitter 10 and is also used to output the frequency-converted laser light. The second beam splitter 10 is used to reflect the laser light of the first wavelength to the third beam splitter 17. The laser light of the first wavelength oscillates in the first resonant cavity to generate the first oscillating laser light 1-1. The first oscillating laser light 1-1 does not output the first resonant cavity.

[0044] The third reflector 16 is used to reflect the laser light of the second wavelength. The second output mirror 13 is used to reflect the laser light of the second wavelength back to the third reflector 16. The laser light of the second wavelength oscillates in the second resonant cavity to generate the second oscillating laser light 2-1. The second output mirror 13 is also used to transmit the second oscillating laser light 2-1 out of the second resonant cavity and inject it into the first resonant cavity through the second beam splitter 10.

[0045] The birefringent filter 2 is placed between the first laser gain module 18 and the second mirror 15. The birefringent filter 2 is placed in the Brewster angle mode and is used to convert the laser of the first wavelength into the laser of the first wavelength with a horizontal polarization state. The intensity of the first oscillating laser is adjusted by adjusting the angle of the birefringent filter 2.

[0046] The device further includes a fourth mirror and a shaping lens. Figure 2 The fourth mirror is a mirror group, including a first highly reflective mirror 6, a second highly reflective mirror 9, and a third highly reflective mirror 12. The shaping lens can be a shaping lens group, and the shaping lens group includes a first lens 7 and a second lens 8. The first lens 7 and the second lens 8 are arranged between the first highly reflective mirror 6 and the second output mirror 13. The first lens 7 and the second lens 8 are used to shape the second oscillating laser 2-1. The first highly reflective mirror 6, the second highly reflective mirror 9, and the third highly reflective mirror 12 are used to reflect the shaped second oscillating laser 2-1. The shaped second oscillating laser 2-1 is reflected by the second beam splitter 10 and injected into the first resonant cavity. The positions and angles of the first highly reflective mirror 6, the second highly reflective mirror 9, and the third highly reflective mirror 12 are adjusted to make the first oscillating laser 1-1 collinear with the shaped second oscillating laser 2-1, realizing phase matching, achieving the highest frequency conversion efficiency and high output efficiency of the frequency-converted laser.

[0047] A temperature regulation module for regulating the temperature of the nonlinear crystal 11 is arranged inside the nonlinear crystal 11 to avoid the decrease in the laser output power and the laser beam quality caused by the non-uniform temperature field inside the nonlinear crystal 11. The first laser gain module 18 includes a first laser gain medium and a first pump source, and further includes a first cooling module for cooling the first laser gain medium. Among them, the material of the first laser gain medium can be a crystal or glass, and the pumping method of the first pump source can be side pumping and / or end pumping, and can also be continuous pumping or quasi-continuous pumping. The second laser gain module 14 includes a second laser gain medium and a second pump source, and further includes a second cooling module for cooling the second laser gain medium.

[0048] The third beam splitter 17 is coated with a high-reflection film for the first oscillating laser 1-1, and is also coated with a high-transmission film for the second oscillating laser 2-1 and the frequency-converted laser 3-1. The second mirror 15 is coated with a high-reflection film for the first oscillating laser 1-1. The third mirror 16 is coated with a high-reflection film for the second oscillating laser .....

[0049] The composite cavity non-linear laser frequency conversion device provided by the present invention couples a first resonant cavity and a second resonant cavity to form a composite resonant cavity, and realizes the frequency conversion of a laser beam through the combination of in-cavity frequency conversion and out-of-cavity frequency conversion with a non-linear crystal, which is easy to achieve the mode matching of the non-linear crystal and effectively improves the frequency conversion efficiency; moreover, the laser optical path of the present invention is easy to adjust, the structure is compact, the design is flexible, and it is easy to achieve the matching of the in-cavity and out-of-cavity laser phases.

[0050] In the first specific embodiment of the present invention, as Figure 1 a composite cavity non-linear frequency conversion laser device based on Nd:YAG, the device includes a first resonant cavity, a second resonant cavity, a laser gain module 3, a non-linear crystal 11, a birefringent filter 2, a first high reflector 6, a first lens 7, a second lens 8 and a second high reflector 9. Among them, the first resonant cavity includes a first mirror 1, a first beam splitter 4, a second beam splitter 10 and a birefringent filter 2; the second resonant cavity includes a first mirror 1, a first output mirror 5 and a birefringent filter 2. The laser gain module 3 includes a laser gain medium and a pump source (the laser gain medium and the pump source are not shown in Figure 1 ), the material of the laser gain medium can be a crystal or glass, the pumping method of the pump source can be side pumping and / or end pumping, and can also be continuous pumping or quasi-continuous pumping. The laser gain medium also includes a cooling device (the cooling device is not shown in Figure 1 ). In this embodiment, water cooling is carried out through cooling water to prevent the internal temperature of the laser gain medium from being too high, which may cause the decrease of the laser output power and the quality of the laser beam. In this embodiment, the material of the laser gain medium is a Nd:YAG crystal, the doping concentration is 1%, the size is D3 mm×80mm, D3mm represents the outer diameter of the crystal rod is 3mm, and the surface of the Nd:YAG crystal rod is coated with high-transmission films for 808nm, 1064nm and 1319nm lasers, and the transmittance of the high-transmission film is greater than 99%; the pump source is a quasi-continuous semiconductor 808nm laser, and the quasi-continuous 1064nm laser and 1319nm laser are output by side pumping. The laser of the first wavelength is 1319nm laser, and the laser of the second wavelength is 1064nm laser.

[0051] The first resonant cavity includes a first mirror 1, a first beam splitter 4, a second beam splitter 10, and a birefringent filter 2. The second resonant cavity includes a first mirror 1, a first output mirror 5, and a birefringent filter 2. The first resonant cavity and the second resonant cavity are coupled to form a composite cavity. A laser gain module 3 is disposed between the birefringent filter 2 and the first beam splitter 4 to output 1064 nm laser and 1319 nm laser. The birefringent filter 2 is a quartz crystal placed at the Brewster angle, which converts the 1319 nm laser into a 1319 nm laser with horizontal polarization state and the 1064 nm laser into a 1064 nm laser with horizontal polarization state. By rotating the angle of the birefringent filter 2, the intensities of the 1064 nm oscillating laser and the 1319 nm oscillating laser can be adjusted. After adjustment, the intensities of the 1064 nm oscillating laser and the 1319 nm oscillating laser can be the same or different. In this embodiment, the intensities of the 1064 nm oscillating laser and the 1319 nm oscillating laser are adjusted to be equal.

[0052] The first oscillating laser 1-1 generated by the first resonant cavity is a 1319 nm oscillating laser, which does not output from the resonant cavity. The second oscillating laser 2-1 generated by the second resonant cavity is a 1064 nm oscillating laser, which is output from the second resonant cavity through the first output mirror 5. After the second oscillating laser 2-1 is reflected by the first highly reflective mirror 6, it is shaped by the first lens 7 and the second lens 8 and then reflected by the second beam splitter 10 and injected into the first resonant cavity. The first oscillating laser 1-1 and the shaped second oscillating laser 2-1 are frequency-converted by the nonlinear crystal 11 to generate a frequency-converted laser 3-1, which is output by the first beam splitter 4. The frequency-converted laser 3-1 is a 589 nm frequency-converted laser.

[0053] On the surface of the first mirror 1 close to the birefringent filter 2, a high-reflection film for 1064 nm oscillating laser and 1319 nm oscillating laser is coated, with a reflectivity greater than 99%. On the surface of the first beam splitter 4 close to the birefringent filter 2, a high-reflection film for 1319 nm oscillating laser is coated, with a reflectivity greater than 99%, and a high-transmission film for 1064 nm oscillating laser and 589 nm frequency-converted laser is coated, with a transmittance greater than 99%. On the surface of the second beam splitter 10 close to the first beam splitter 4, a high-reflection film for 1319 nm oscillating laser and 589 nm frequency-converted laser is coated, with a reflectivity greater than 99%. On the surface far from the first beam splitter 4, a high-transmission film for 1064 nm oscillating laser is coated, with a transmittance greater than 99%. On the surface of the first output mirror 5 close to the birefringent filter 2, a partial antireflection film for 1064 nm oscillating laser is coated, and the transmittance of the partial antireflection film is 20%.

[0054] Figure 1The first high reflector 6 and the second high reflector 9 are used to adjust the optical path of part of the second oscillating laser output from the second resonator, so that the second oscillating laser 2-1 injected into the first resonator is collinear with the first oscillating laser 1-1; the shaping lens is a shaping lens group, including a first lens 7 and a second lens 8. The first lens 7 and the second lens 8 are arranged between the first high reflector 6 and the second high reflector 9, and are used to shape the 1064nm oscillating laser output from the second resonator to achieve mode matching with the 1319nm oscillating laser in the first resonator. Both the first high reflector 6 and the second high reflector 9 are coated with a high-reflection film for the 1064nm oscillating laser, with a reflectivity greater than 99%. The second high reflector 9 is used to reflect the shaped 1064nm oscillating laser from outside the second resonator into the first resonator cavity to achieve the combination of inside and outside the cavity; by adjusting the angle between the first high reflector 6 and the second high reflector 9, the shaped 1064nm oscillating laser is made collinear with the 1319nm oscillating laser, and the phase matching condition of the nonlinear crystal 11 is satisfied.

[0055] The nonlinear crystal 11 is an LBO crystal. The cutting angles of the nonlinear crystal 11 are θ = 90° and φ = 0°, and the temperature is controlled at 40°C to meet the best phase matching required for the sum frequency of the 1064nm oscillating laser and the 1319nm oscillating laser to 589nm; the surface of the nonlinear crystal 11 is coated with a high-transmission film for the 1064nm oscillating laser, the 1319nm oscillating laser and the 589nm frequency-converted laser, with a transmittance greater than 99%. The generated frequency-converted laser is output by the first beam splitter 4; the nonlinear crystal 11 includes a temperature adjustment module. In this embodiment, the temperature adjustment module is a temperature controller (the temperature controller is not shown in Figure 1 ). The nonlinear crystal 11 detects the temperature through the temperature controller and controls the temperature in real time; the temperature controller includes a crystal heating furnace and a temperature sensor. The crystal heating furnace is made of copper, and the temperature sensor is a platinum resistor. The current output is controlled by the PID algorithm to control the heating of the crystal heating furnace, and the temperature control accuracy is ±0.05 to avoid the influence of the poor sum frequency effect caused by the uneven temperature field of the nonlinear crystal 11. The nonlinear crystal 11 is arranged in the first resonator, combining the methods of intracavity frequency conversion and extracavity frequency conversion, to achieve the characteristics of high intracavity frequency conversion efficiency and easy mode matching of the nonlinear crystal for extracavity frequency conversion.

[0056] Specifically, the laser gain module 3 emits 1064 nm laser and 1319 nm laser through side pumping. The first and second oscillating lasers are generated in the first resonant cavity and the second resonant cavity respectively. The first oscillating laser is 1319 nm oscillating laser, and this laser does not output from the first resonant cavity; the second oscillating laser is 1064 nm oscillating laser, and this laser is output from the second resonant cavity by the first output mirror 5; by adjusting the angle of the birefringent filter 2, the intensities of the 1064 nm oscillating laser and the 1319 nm oscillating laser are made equal to ensure the generation of a high-power and high-quality laser beam during sum frequency mixing; the 1064 nm oscillating laser is shaped through reflection by the first high reflector 6 and passing through the first lens 7 and the second lens 8 to achieve mode matching between the 1064 nm oscillating laser and the 1319 nm oscillating laser; the angle between the first high reflector 6 and the second high reflector 9 is adjusted so that the shaped 1064 nm oscillating laser is reflected by the second high reflector 9 into the first resonant cavity to make the 1319 nm oscillating laser and the 1064 nm oscillating laser collinear and satisfy the phase matching of the LBO crystal; the LBO crystal is placed in the first resonant cavity to achieve efficient frequency conversion of the 1064 nm and 1319 nm oscillating lasers, generating a 589 nm frequency-converted laser with high power and high beam quality, and the frequency-converted laser is output from the first beam splitter 4 to the outside of the first resonant cavity.

[0057] In this embodiment, the 1064 nm oscillating laser is reflected by the first high reflector 6, shaped by the first lens 7 and the second lens 8, and the shaped 1064 nm oscillating laser is reflected by the second high reflector 9 and injected into the first resonant cavity by adjusting the angle between the first high reflector 6 and the second high reflector 9 to make the 1064 nm oscillating laser collinear with the 1319 nm oscillating laser and satisfy the phase matching condition of the nonlinear crystal; the 1319 nm oscillating laser and the 1064 nm oscillating laser are frequency-converted by the nonlinear crystal 11 to generate a 589 nm frequency-converted laser. The composite cavity nonlinear laser frequency conversion device of this embodiment has a compact structure, combines the advantages of intracavity sum frequency mixing and extracavity sum frequency mixing, has the advantages of high sum frequency efficiency, easy adjustment of laser collinearity, and good laser mode matching, and can generate a frequency-converted laser with high conversion efficiency, high power, and high beam quality.

[0058] In the second specific embodiment of the present invention, Figure 2 It is a composite cavity nonlinear frequency conversion laser device based on Nd:YAG and Nd:YVO4. The device includes a first laser gain module 18, a second laser gain module 14, a first resonant cavity, a second resonant cavity, a birefringent filter 2, and a nonlinear crystal 11.

[0059] The first laser gain module 18 is placed in the first resonant cavity to generate a laser with a wavelength of 1319 nm. The 1319-nm laser oscillates in the first resonant cavity to generate the first oscillating laser 1-1, and the first oscillating laser 1-1 is a 1319-nm oscillating laser, which does not output from the first resonant cavity. The first laser gain module 18 includes a first laser gain medium and a first pump source (the first laser gain medium and the first pump source are not shown in Figure 2 ), and the first laser gain module 18 further includes a first cooling module for cooling the first laser gain medium (the first cooling module is not shown in Figure 2 ). The second laser gain module 14 is disposed in the second resonant cavity to generate a laser with a wavelength of 1064 nm. The second resonant cavity generates and outputs the second oscillating laser 2-1, and the second oscillating laser 2-1 is a 1064-nm oscillating laser. The second laser gain module 14 includes a second laser gain medium and a second pump source (the second laser gain medium and the second pump source are not shown in Figure 2 ). The material of the second laser gain medium can be a crystal or glass. The pumping method of the second pump source can be side pumping and / or end pumping, and can also be continuous pumping or quasi-continuous pumping. The second laser gain module 14 further includes a second cooling module for cooling the second laser gain medium (the second cooling module is not shown in Figure 2 ). In this embodiment, both the first cooling module and the second cooling module are water-cooled by cooling water to prevent the internal temperature of the second laser gain medium from being too high, which may cause a decrease in the laser output power and the laser beam quality. In this embodiment, the material of the first laser gain medium is Nd:YAG crystal, and the material of the second laser gain medium is Nd:YVO4 crystal; both the first pump source and the second pump source are quasi-continuous operation semiconductor 808-nm lasers, and both the first pump source and the second pump source adopt the side pumping method. The first laser gain module generates a 1319-nm laser, and the second laser gain module generates a 1064-nm laser with a horizontal polarization direction.

[0060] The first laser gain medium is a Nd:YAG crystal rod with a doping concentration of 1%, a size of D3 mm×80 mm, and a high-transmission film for 808-nm and 1319-nm lasers is coated on the surface of the Nd:YAG crystal rod, with a transmittance greater than 99%; the second laser gain medium is a Nd:YVO4 crystal rod with a doping concentration of 1%, a size of 20 mm×3 mm×3 mm for the crystal rod, and a high-transmission film for 808-nm and 1064-nm lasers is coated on the surface of the Nd:YVO4 crystal rod, with a transmittance greater than 99%.

[0061] The first resonant cavity includes a second mirror 15, a third beam splitter 17, a second beam splitter 10, and a birefringent filter 2. The second resonant cavity includes a third mirror 16 and a second output mirror 13. The first resonant cavity and the second resonant cavity are coupled to form a composite resonant cavity. The first laser gain module 18 is placed in the first resonant cavity to output a laser with a wavelength of 1319 nm. The birefringent filter 2 is a quartz crystal and is placed at the Brewster angle to convert the 1319-nm oscillating laser in the first resonant cavity into a laser with a first wavelength in the horizontal polarization state. By rotating the angle of the birefringent filter 2, the intensity of the 1319-nm oscillating laser is adjusted. The intensity of the 1319-nm oscillating laser after adjustment can be the same as or different from the intensity of the 1064-nm oscillating laser generated by the second resonant cavity.

[0062] The first oscillating laser 1-1 generated by the first resonant cavity is a 1319-nm oscillating laser, and this laser does not output from the resonant cavity. The second laser gain module 14 outputs a laser with a second wavelength in the horizontal polarization state. The second oscillating laser 2-1 generated by the second resonant cavity is a 1064-nm oscillating laser, which is output from the second resonant cavity through the second output mirror 13. The second oscillating laser 2-1 is injected into the first resonant cavity through the second beam splitter 10. The first oscillating laser 1-1 and the second oscillating laser 2-1 are frequency-converted by a nonlinear crystal 11 to generate a frequency-converted laser 3-1. The frequency-converted laser 3-1 is output from the first resonant cavity by the third beam splitter 17. The frequency-converted laser 3-1 is a 589-nm frequency-converted laser.

[0063] On the surface of the second mirror 15 close to the birefringent filter 2, a high-reflection film for the 1319-nm oscillating laser is coated, and the reflectivity is greater than 99%. On the surface of the third beam splitter 17 close to the birefringent filter 2, a high-reflection film for the 1319-nm oscillating laser is coated, and the reflectivity is greater than 99%. A high-transmission film for the 589-nm frequency-converted laser is also coated, and the transmittance is greater than 99%. On the surface of the second beam splitter 10 close to the third beam splitter 17, high-reflection films for the 1319-nm oscillating laser and the 589-nm frequency-converted laser are coated, and the reflectivity is greater than 99%. On the surface far from the third beam splitter 17, a high-transmission film for the 1064-nm oscillating laser is coated, and the transmittance is greater than 99%. On the surface of the third mirror 16 close to the second laser gain module 14, a high-reflection film for the 1064-nm oscillating laser is coated, and the reflectivity is greater than 99%. The second output mirror 13 is coated with a partial antireflection film for the 1064-nm oscillating laser, and the transmittance of the partial antireflection film is 40%.

[0064] The shaping lens in this embodiment is a shaping lens group, including a first lens 7 and a second lens 8. The first lens 7 and the second lens 8 are arranged between the second output mirror 13 and the first high-reflection mirror 6, and are used to shape a part of the 1064nm oscillating laser output from the second resonant cavity, so that the shaped 1064nm oscillating laser matches the mode of the 1319nm oscillating laser in the first resonant cavity; The fourth mirror is a mirror group, including a first high-reflection mirror 6, a second high-reflection mirror 9 and a third high-reflection mirror 12. The first high-reflection mirror 6, the third high-reflection mirror 12 and the second high-reflection mirror 9 are all coated with a high-reflection film for 1064nm oscillating laser, and the reflectivity is greater than 99%; The mirror group is used to reflect the shaped 1064nm oscillating laser, and inject the shaped 1064nm oscillating laser from outside the second resonant cavity into the first resonant cavity, realizing the combination of inside and outside the cavity; Adjust the positions and angles of the first high-reflection mirror 6, the second high-reflection mirror 9 and the third high-reflection mirror 12 to make the shaped 1064nm oscillating laser collinear with the 1319nm oscillating laser and meet the phase matching condition of the nonlinear crystal 11.

[0065] The birefringent filter 2 is a quartz crystal. The birefringent filter 2 is arranged between the first laser gain module 18 and the second mirror 15, and is set at the Brewster angle to convert the 1319nm laser inside the first resonant cavity into 1319nm laser with horizontal polarization state; The intensity of the 1319nm oscillating laser is adjusted by adjusting the angle of the birefringent filter 2.

[0066] The nonlinear crystal 11 is an LBO crystal. The cutting angles of the nonlinear crystal are θ = 90°, φ = 0°, and the temperature is controlled at 40°C, meeting the best phase matching required for the sum frequency of 1064nm oscillating laser and 1319nm oscillating laser to 589nm; The surface of the nonlinear crystal is coated with a high-transmission film for 1064nm oscillating laser, 1319nm oscillating laser and 589nm frequency-converted laser, and the transmittance is greater than 99%. The generated frequency-converted laser is output by the third beam splitter 17; The nonlinear crystal 11 includes a temperature adjustment module. In this embodiment, the temperature adjustment module is a temperature controller (the temperature controller is not shown in Figure 2 ). The nonlinear crystal 11 detects the temperature through the temperature controller and controls the temperature in real time; The temperature controller includes a crystal heating furnace and a temperature sensor. The crystal heating furnace is made of copper, and the temperature sensor is a platinum resistance. The current output is controlled by the PID algorithm to control the heating of the crystal heating furnace, and the temperature control accuracy is ±0.05, avoiding the influence of the poor sum frequency effect caused by the uneven temperature field of the nonlinear crystal 11. The nonlinear crystal 11 is arranged in the first resonant cavity, combining the methods of intracavity frequency conversion and extracavity frequency conversion, realizing the characteristics of high intracavity frequency conversion efficiency and easy mode matching of the nonlinear crystal for extracavity frequency conversion.

[0067] Specifically, the first laser gain module 18 emits 1319 nm laser through side pumping, and forms 1319 nm oscillating laser by oscillating in the first resonant cavity, and this laser does not output from the first resonant cavity; the second laser gain module 14 emits 1064 nm laser through side pumping, and forms 1064 nm oscillating laser by oscillating in the second resonant cavity, and outputs from the second resonant cavity; the 1064 nm oscillating laser is shaped by the first lens 7 and the second lens 8, and the mode matching between the 1064 nm oscillating laser and the 1319 nm oscillating laser is achieved; the shaped 1064 nm oscillating laser is reflected by the first high reflection mirror 6, the third high reflection mirror 12 and the second high reflection mirror 9 and injected into the first resonant cavity, so as to make the 1319 nm oscillating laser and the 1064 nm oscillating laser collinear and meet the phase matching of the LBO crystal; the 1319 nm oscillating laser and the shaped 1064 nm oscillating laser are frequency-converted by the nonlinear crystal 11 to generate 589 nm frequency-converted laser with high power and high beam quality, and the frequency-converted laser is output to the outside of the first resonant cavity by the third beam splitter 17.

[0068] In this embodiment, the 1064 nm oscillating laser generated by the second resonant cavity is shaped by the first lens 7 and the second lens 8. By adjusting the angles between the first high reflection mirror 6, the third high reflection mirror 12 and the second high reflection mirror 9, the shaped 1064 nm laser is injected into the first resonant cavity to make the 1064 nm oscillating laser collinear with the 1319 nm oscillating laser and meet the phase matching condition of the nonlinear crystal; the 1319 nm oscillating laser and the 1064 nm oscillating laser are frequency-converted into 589 nm frequency-converted laser by the nonlinear crystal 11. This laser device has a compact structure, combines the advantages of intracavity sum frequency and extracavity sum frequency, has the advantages of high sum frequency efficiency, easy adjustment of laser collinearity and good laser mode matching, and can generate frequency-converted laser with high conversion efficiency, high power and high beam quality.

[0069] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. Unless otherwise clearly specified and defined, the terms "mounted", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0070] It should also be noted that in the description of the present invention, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A composite cavity non-linear laser frequency conversion device, characterized in that, The device includes a laser gain module, a first resonator, a second resonator, and a nonlinear crystal, and the nonlinear crystal is disposed in the first resonator; The laser gain module is configured to emit a laser of a first wavelength and a laser of a second wavelength; The first resonator is configured to generate a first oscillating laser, the wavelength of the first oscillating laser being the first wavelength, and the first oscillating laser does not output from the first resonator; The second resonator is configured to generate a second oscillating laser, inject the second oscillating laser into the first resonator, and the wavelength of the second oscillating laser is the second wavelength; The nonlinear crystal is configured to frequency-convert the first oscillating laser and the second oscillating laser to generate a frequency-converted laser, and the frequency-converted laser is output from the first resonator; The first resonator includes a first mirror, a first beam splitter, and a second beam splitter, the second resonator includes a first mirror and a first output mirror, the laser gain module is disposed between the first mirror and the first beam splitter, and the nonlinear crystal is disposed between the first beam splitter and the second beam splitter; The first mirror is configured to reflect the laser of the first wavelength and the laser of the second wavelength, the first beam splitter is configured to reflect the laser of the first wavelength to the second beam splitter and transmit through the nonlinear crystal, and the first beam splitter is further configured to transmit the laser of the second wavelength and output the frequency-converted laser; the second beam splitter is configured to reflect the laser of the first wavelength back to the first beam splitter and the first mirror, the laser of the first wavelength oscillates in the first resonator to generate a first oscillating laser, and the second beam splitter is further configured to transmit the second oscillating laser; The first output mirror is configured to reflect the laser of the second wavelength back to the first mirror to generate a second oscillating laser, transmit the second oscillating laser out of the second resonator, and inject the second oscillating laser into the first resonator through the second beam splitter.

2. The device according to claim 1, characterized in that, The device further includes a birefringent filter disposed between the laser gain module and the first mirror, and the birefringent filter is placed in a Brewster angle manner and is configured to convert the laser of the first wavelength into a laser of the first wavelength with a horizontal polarization state and convert the laser of the second wavelength into a laser of the second wavelength with a horizontal polarization state; The birefringent filter is further configured to adjust the intensities of the first oscillating laser and the second oscillating laser.

3. The device according to any one of claims 1-2, characterized in that The device further includes a shaping lens configured to shape the second oscillating laser output from the second resonator so that the second oscillating laser and the first oscillating laser achieve mode matching.

4. The device according to any one of claims 1-2, characterized in that The device further includes a fourth mirror configured to adjust the optical path of the second oscillating laser output from the second resonator so that the second oscillating laser injected into the first resonator is collinear with the first oscillating laser.

5. The device according to any one of claims 1-2, characterized in that The device further includes a temperature adjustment module configured to adjust the temperature of the nonlinear crystal.

6. The device according to any one of claims 1-2, characterized in that, The laser gain module includes a laser gain medium and a pump source, and the device further includes a cooling module configured to cool the laser gain medium.

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