A solid-state anti-Stokes Raman laser

Abstract

The invention discloses a solid anti-Stokes Raman laser, comprising a laser diode pump source and a resonant cavity. The wavelength of the laser diode pump source is 808nm, and it can be a laser diode side pump source or a laser diode end pump source. The resonant cavity comprises a back cavity mirror, a coupling mirror and an output mirror. A laser gain medium and a Q-switching device are placed between the back cavity mirror and the coupling mirror in the resonant cavity, and a Raman crystal is placed between the coupling mirror and the output mirror. The technical scheme makes full use of the high peak power of the fundamental frequency Q-switched pulse and the high power density of the Raman light in the cavity, and realizes collinear four-wave mixing by utilizing the anisotropy of the Raman crystal, thereby improving the performance of the anti-Stokes Raman laser, solving the disadvantage that the existing laser beam cannot be collinear, and providing a new all-solid anti-Stokes Raman laser with small size, low cost and good stability.

Description

Technical Field

[0001] The invention belongs to the field of laser technology and relates to a solid anti-Stokes Raman laser. Background Art

[0002] All-solid-state laser (DPL, Diode Pumped solid state Laser) is a solid laser that uses a semiconductor laser (LD) as the pumping source. The laser working material, excitation source and other parts of DPL are all made of solid materials. It combines the advantages of traditional solid lasers and semiconductor lasers, becoming one of the most promising new generation laser sources.

[0003] Current lasers cannot cover all wavelength ranges. To meet the application needs in more fields, we need to use special methods to generate special wavelengths with high efficiency. Crystal Raman lasers are one of the important methods to expand laser wavelengths. Anti-Stokes Raman scattering can achieve frequency up-conversion, so solid anti-Stokes lasers have become an important way to further expand the existing laser spectrum range. From the essence of anti-Stokes scattering, it is a four-wave mixing process of two pump light photons, one Stokes light photon and one anti-Stokes light photon. The four light fields are coupled to each other in the crystal and need to meet the phase matching condition Δ k =2 k P - k S - k AS =0, where k P , k S and k AS are the wave vectors of pump light, Stokes light and anti-Stokes light respectively.

[0004] In the solid anti-Stokes laser reported in the prior art, in order to meet the phase matching condition, there is a certain angle between the propagation directions of the pump light, Stokes light and anti-Stokes light, which leads to insufficient utilization of the light intensity and limits the conversion efficiency of the laser. Summary of the invention

[0005] In order to overcome the defects of the prior art and improve the conversion efficiency of anti-Stokes light, the present invention provides a solid anti-Stokes Raman laser.

[0006] A solid anti-Stokes Raman laser comprises a laser diode pump source and a resonant cavity;

[0007] The wavelength of the laser diode pump source is 808nm, and it can be a laser diode side pump source or a laser diode end pump source;

[0008] The laser diode side pump source comprises a driving power supply, a laser diode side pump module, and a cooling device;

[0009] The laser diode end face pumping source comprises a driving power supply, a laser diode, a cooling device, an optical fiber and a coupling lens group;

[0010] The resonant cavity comprises a rear cavity mirror, a coupling mirror and an output mirror, a laser gain medium and a Q-switching device are placed between the rear cavity mirror and the coupling mirror in the resonant cavity, and a Raman crystal is placed between the coupling mirror and the output mirror;

[0011] The laser gain medium, Q-switching device and Raman crystal are all temperature-controlled by a cooling device;

[0012] The laser gain medium is neodymium-doped yttrium aluminum garnet (Nd:YAG) with a doping concentration of 0.05-at.% to 3-at.%. In the case of laser diode side pumping, both end faces are coated with anti-reflection films in the 1000 nm-1200 nm band; in the case of laser diode end pumping, both end faces are coated with anti-reflection films in the 808 nm and 1000 nm-1200 nm bands.

[0013] The Q-switching device is an acousto-optic Q-switching device, which consists of a radio frequency input device and a Q-switching crystal. Both end faces of the Q-switching crystal are coated with an anti-reflection film in the 1000 nm-1200 nm band. The modulation frequency is 1-50 KHz. By inputting radio frequency waves to change the refractive index distribution of the Q-switching crystal, the purpose of periodically changing the threshold of the laser resonant cavity is achieved, thereby playing the role of a Q-switching switch.

[0014] The Raman crystal can be one of yttrium vanadate YVO4 crystal and barium tungstate BaWO4 crystal; both end faces of the Raman medium are coated with anti-reflection films in the 900 nm-1200 nm band. The Raman crystal can be cut in different directions and angles according to phase matching and other needs to achieve the colinear interaction of fundamental frequency light, Stokes light and anti-Stokes light, thereby effectively improving the performance of the laser.

[0015] The back cavity mirror is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band when the laser diode is pumped from the side; and is coated with an 808 nm anti-reflection film and a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band when the laser diode is end-face pumped.

[0016] Both end faces of the coupling mirror are plated with a transmission film with a transmission range of more than 90% in the 1064 nm band, and the front end face is also plated with a reflection film with a reflectivity of more than 90% near the wavelength of 1180±1 nm and a reflection film with a reflectivity of more than 90% near the wavelength of 970±2 nm, wherein the front end face is the end close to the output mirror;

[0017] The output mirror is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band, and the film has a transmittance greater than 90% in the transmission range for anti-Stokes light near 970±1 nm.

[0018] The cavity length of the resonant cavity is 20 cm-50 cm, and the curvature radius of the rear cavity mirror and the output mirror of the resonant cavity can be selected according to actual conditions.

[0019] In the case of the laser diode side pumping, the relative positions of the side pump module, the laser gain medium and the Q-switching switch in the resonant cavity can be interchanged.

[0020] The cooling device has two modes: circulating water cooling and semiconductor refrigeration; circulating water cooling - the sides of the crystal are wrapped with metal blocks with pipes, and circulating cooling water is continuously passed through the pipes of the metal blocks to reduce the temperature of the crystal; semiconductor refrigeration - the sides of the crystal are surrounded by semiconductor refrigeration blocks.

[0021] The lengths of all crystals in the present invention can be selected according to specific requirements; the end face shape and area of ​​the crystal can be determined according to the area of ​​the beam cross section.

[0022] In the technical solution of the present invention, the working process of the solid anti-Stokes Raman laser is as follows: the pumping light with a wavelength of 808 nm emitted by the laser diode pump source is coupled into the Nd:YAG laser crystal, and when the Q-switch of the Q-switch device is turned off, the pumping light is converted into inversion particles and stored; when the Q-switch is turned on, a large number of accumulated inversion particles are instantly converted into fundamental frequency light through stimulated radiation; the fundamental frequency light with higher peak power passes through the Raman crystal and is converted into Raman light due to stimulated Raman scattering; at the same time, the fundamental frequency light, Stokes light and anti-Stokes light are four-wave mixed in the Raman crystal, and the generated anti-Stokes light is output by the output mirror.

[0023] Since the Raman effect and the four-wave mixing effect are both third-order nonlinear effects, the fundamental frequency light needs to have a higher peak power. By using a Q-switching device in the laser, the peak power of the fundamental frequency light can be increased, and the conversion efficiency of the fundamental frequency light to anti-Stokes light can be improved, which effectively improves the performance of the laser.

[0024] The laser proposed by the present invention can adopt a coupled cavity type and a new combination mode, effectively compress the volume of the anti-Stokes Raman laser, adopt the Q-switching technology, make full use of the high peak power of the fundamental frequency Q-switched pulse and the high power density of the Raman light in the cavity, and realize the collinear four-wave mixing by utilizing the anisotropy of the Raman crystal, thereby improving the performance of the anti-Stokes Raman laser, successfully solving the disadvantage that the above-mentioned laser light beams cannot be collinear, and providing a new all-solid anti-Stokes Raman laser with small volume, low cost and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the optical path structure of the laser diode end-pumped laser of the present invention;

[0026] Figure 2 It is a schematic diagram of the optical path structure of the laser diode side pumping laser of the present invention;

[0027] Among them: 1. Laser diode end pump source, 2. Back cavity mirror, 3. Laser gain medium, 4. Q-switching device, 5. Coupling mirror, 6. Raman crystal, 7. Output mirror, 8. Laser diode side pump source. DETAILED DESCRIPTION

[0028] The present invention is further illustrated by the following examples, but is not limited to the following examples.

[0029] Embodiment 1:

[0030] like Figure 1 As shown, a solid anti-Stokes Raman laser comprises a laser diode pump source and a resonant cavity;

[0031] The wavelength of the laser diode pump source is 808nm, which is the laser diode end face pump source 1;

[0032] A laser diode end-face pumping source 1, comprising a driving power supply, a laser diode, a cooling device, an optical fiber and a coupling lens group;

[0033] The resonant cavity comprises a back cavity mirror 2, a coupling mirror 5 and an output mirror 7, a laser gain medium 3 and a Q-switching device 4 are placed between the back cavity mirror 2 and the coupling mirror 5 in the resonant cavity, and a Raman crystal 6 is placed between the coupling mirror 5 and the output mirror 7;

[0034] The laser gain medium 3, the Q-switching device 4 and the Raman crystal 6 are all temperature-controlled by a cooling device;

[0035] The laser gain medium 3 is neodymium-doped yttrium aluminum garnet (Nd:YAG), with a size of Ф5mm×5mm and a doping concentration of 1-at.%. In the case of laser diode end-face pumping, both end faces are coated with anti-reflection films of 808nm and 1000nm-1200nm bands.

[0036] The Q-switching device 4 is an acousto-optic Q-switching device, which consists of a radio frequency input device and a Q-switching crystal. The length of the Q-switching crystal is 35 mm, and both end surfaces are coated with an anti-reflection film in the 1000 nm-1200 nm band. The modulation frequency is 10 KHz. By inputting radio frequency waves to change the refractive index distribution of the Q-switching crystal, the purpose of periodically changing the threshold of the laser resonant cavity is achieved, thus playing the role of a Q-switching switch.

[0037] Raman crystal 6 is yttrium vanadate YVO4 crystal, with a size of 3×3×35mm 3 Both ends are coated with 900 nm-1200 nm anti-reflection film. Raman crystal 6 can be made of yttrium vanadate YVO4 crystal according to phase matching and other needs. θ =4.05 degrees, Ф=0 degrees angle cutting, to achieve the fundamental frequency light, Stokes light and anti-Stokes light co-linear interaction, so as to effectively improve the performance of the laser.

[0038] The radius of curvature of the back cavity mirror 2 is 3000 mm, and when the laser diode end face is pumped, it is coated with an 808 nm anti-reflection film and a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band;

[0039] The coupling mirror 5 is a flat mirror, both end faces are plated with a transmission film with a transmission range of more than 90% in the 1064 nm band, and the front end face is also plated with a reflection film with a reflectivity of more than 90% near the 1179 nm wavelength and a reflection film with a reflectivity of more than 90% near the 972 nm wavelength, wherein the front end face is the end close to the output mirror 7;

[0040] The output mirror 7 is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band, and the film has a transmittance greater than 90% in the transmission range for anti-Stokes light near 970 nm.

[0041] The cavity length of the resonant cavity is 20 cm-50 cm, and the curvature radius of the rear cavity mirror 2 and the output mirror 7 of the resonant cavity can be selected according to actual conditions.

[0042] The lengths of all crystals in this technical solution can be selected according to specific requirements; the end face shape and area of ​​the crystal can be determined according to the area of ​​the beam cross section.

[0043] The working process of the laser is as follows: the laser diode end-face pump source 1 emits a pump light with a wavelength of 808 nm, which enters the neodymium-doped yttrium aluminum garnet Nd:YAG crystal through the optical fiber and the coupling lens. When the Q-switching switch of the acousto-optic Q-switching device 4 is turned off, the pump light is converted into inversion particles of the laser gain medium 3 and stored; when the Q-switch is turned on, the accumulated large number of inversion particles are instantly converted into fundamental frequency light with a wavelength of 1064 nm through stimulated radiation; the fundamental frequency light with a higher peak power passes through the yttrium vanadate YVO4 crystal and is converted into 972 nm anti-Stokes light due to stimulated Raman scattering.

[0044] Embodiment 2:

[0045] like Figure 2 As shown, a solid anti-Stokes Raman laser comprises a laser diode pump source and a resonant cavity;

[0046] The wavelength of the laser diode pump source is 808 nm, which is the laser diode side pump source 8;

[0047] A laser diode side pump source 8, including a driving power supply, a laser diode side pump module, and a cooling device;

[0048] The resonant cavity comprises a back cavity mirror 2, a coupling mirror 5 and an output mirror 7, a laser gain medium 3 and a Q-switching device 4 are placed between the back cavity mirror 2 and the coupling mirror 5 in the resonant cavity, and a Raman crystal 6 is placed between the coupling mirror 5 and the output mirror 7;

[0049] The laser gain medium 3, the Q-switching device 4 and the Raman crystal 6 are all temperature-controlled by a cooling device;

[0050] The laser gain medium 3 is neodymium-doped yttrium aluminum garnet (Nd:YAG), with a size of Ф4mm×5mm and a doping concentration of 2-at.%. In the case of laser diode side pumping, both end faces are coated with anti-reflection films in the 1000 nm-1200 nm band.

[0051] The Q-switching device 4 is an acousto-optic Q-switching device, which consists of a radio frequency input device and a Q-switching crystal. The length of the Q-switching crystal is 35 mm, and both end faces of the Q-switching crystal are coated with an anti-reflection film in the 1000 nm-1200 nm band. The modulation frequency is 50 KHz. By inputting radio frequency waves to change the refractive index distribution of the Q-switching crystal, the purpose of periodically changing the threshold of the laser resonant cavity is achieved, thereby playing the role of a Q-switching switch.

[0052] Raman crystal 6 is a barium tungstate BaWO4 crystal with a size of 4×4×45mm 3 Both ends are coated with 900 nm-1200 nm anti-reflection film. Raman crystal 6 can be used according to phase matching and other needs. BaWO4 crystal θ =18.91 degrees, Ф=0 degrees angle cutting, to achieve the fundamental frequency light, Stokes light and anti-Stokes light co-linear interaction, so as to effectively improve the performance of the laser.

[0053] The radius of curvature of the back cavity mirror 2 is 3000 mm, and when the laser diode is pumped from the side, a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band is applied;

[0054] The coupling mirror 5 is a flat mirror, both end faces are plated with a transmission film with a transmission range of more than 90% in the 1064 nm band, and the front end face is also plated with a reflection film with a reflectivity of more than 90% near the 1180 nm wavelength and a reflection film with a reflectivity of more than 90% near the 969 nm wavelength, wherein the front end face is the end close to the output mirror 7;

[0055] The output mirror 7 is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band, and the film has a transmittance greater than 90% in the transmission range for anti-Stokes light near 969 nm.

[0056] The cavity length of the resonant cavity is 20 cm-50 cm, and the curvature radius of the rear cavity mirror 2 and the output mirror 7 of the resonant cavity can be selected according to actual conditions.

[0057] When the resonant cavity is pumped from the side of the laser diode, the relative positions of the side pump module, the laser gain medium 3, and the Q-switching switch in the resonant cavity can be interchanged.

[0058] The lengths of all crystals in this technical solution can be selected according to specific requirements; the end face shape and area of ​​the crystal can be determined according to the area of ​​the beam cross section.

[0059] The working process of the laser is as follows: the laser diode pump source 1 emits a pump light with a wavelength of 808 nm, which enters the neodymium-doped yttrium aluminum garnet Nd:YAG crystal. When the Q-switch of the acousto-optic Q-switch device 4 is turned off, the pump light is converted into inversion particles of the laser gain medium 3 and stored; when the Q-switch is turned on, the accumulated large number of inversion particles are instantly converted into fundamental frequency light with a wavelength of 1064 nm through stimulated radiation; the fundamental frequency light with a higher peak power passes through the barium tungstate BaWO4 crystal and is converted into 969 nm anti-Stokes light through the stimulated Raman scattering effect.

[0060] The above description is only a specific embodiment of the present invention and cannot be used to limit the scope of implementation of the present invention. Therefore, the replacement of equivalent components or equivalent changes and modifications made according to the patent protection scope of the present invention should still fall within the scope covered by the present invention.

Claims

1. A solid anti-Stokes Raman laser, characterized in that: It includes a laser diode pump source and a resonant cavity; The wavelength of the laser diode pump source is 808nm, and it is a laser diode side pump source or a laser diode end pump source; The laser diode side pump source comprises a driving power supply, a laser diode side pump module, and a cooling device; The laser diode end face pumping source comprises a driving power supply, a laser diode, a cooling device, an optical fiber and a coupling lens group; The resonant cavity comprises a rear cavity mirror, a coupling mirror and an output mirror, a laser gain medium and a Q-switching device are placed between the rear cavity mirror and the coupling mirror in the resonant cavity, and a Raman crystal is placed between the coupling mirror and the output mirror; The laser gain medium, Q-switching device and Raman crystal are all temperature-controlled by a cooling device; The laser gain medium is neodymium-doped yttrium aluminum garnet with a doping concentration of 0.05-at.% to 3-at.%. In the case of side-pumping of the laser diode, both end faces are coated with anti-reflection films of the 1000 nm-1200 nm band; in the case of end-pumping of the laser diode, both end faces are coated with anti-reflection films of the 808 nm and 1000 nm-1200 nm bands; The Q-switching device is an acousto-optic Q-switching device, which is composed of a radio frequency input device and a Q-switching crystal. Both end faces of the Q-switching crystal are coated with an anti-reflection film in the 1000 nm-1200 nm band. The modulation frequency is 1-50 KHz. The refractive index distribution of the Q-switching crystal is changed by inputting radio frequency waves to achieve the purpose of periodically changing the threshold of the laser resonant cavity, thus playing the role of a Q-switching switch. The Raman crystal is a kind of yttrium vanadate YVO4 crystal and barium tungstate BaWO4 crystal. Both end faces of the Raman medium are coated with anti-reflection films in the 900 nm-1200 nm band. The Raman crystal is cut along different directions and angles according to phase matching to achieve the colinear interaction of fundamental frequency light, Stokes light and anti-Stokes light, thereby effectively improving the performance of the laser. The back cavity mirror is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band when the laser diode is pumped from the side, and is coated with an 808 nm anti-reflection film and a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band when the laser diode is end-face pumped; Both end faces of the coupling mirror are plated with a transmission film with a transmission range of more than 90% in the 1064 nm band, and the front end face is also plated with a reflection film with a reflectivity of more than 90% near the wavelength of 1180±1 nm and a reflection film with a reflectivity of more than 90% near the wavelength of 970±2 nm, wherein the front end face is the end close to the output mirror; The output mirror is coated with a reflective film with a reflectivity greater than 90% in the 1000 nm-1200 nm band, and the film has a transmittance greater than 90% in the transmission range for anti-Stokes light near 970±1 nm.

2. The solid-state anti-Stokes Raman laser according to claim 1, characterized in that: The cavity length of the resonant cavity is 20cm-50cm.

3. The solid-state anti-Stokes Raman laser according to claim 1, characterized in that: In the case of the laser diode side pumping, the relative positions of the side pump module, the laser gain medium and the Q-switching switch in the resonant cavity can be interchanged.

4. The solid-state anti-Stokes Raman laser according to claim 1, characterized in that: The cooling device has two modes: circulating water cooling and semiconductor refrigeration.

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