CN219498487U

CN219498487U - Pulse laser

Info

Publication number: CN219498487U
Application number: CN202320472671.2U
Authority: CN
Inventors: 檀慧明; 王军营
Original assignee: Shenzhen Super Laser Technology Co ltd
Current assignee: Shenzhen Super Laser Technology Co ltd
Priority date: 2023-03-03
Filing date: 2023-03-03
Publication date: 2023-08-08
Anticipated expiration: 2033-03-03

Abstract

The application discloses a pulsed laser. The pulse laser comprises a pumping source, a coupling lens group, an input mirror, a gain medium and a loss control device, wherein the coupling lens group, the input mirror, the gain medium and the loss control device are sequentially arranged along the optical axis of the pumping source _、 An output mirror and at least one harmonic crystal. The output mirror comprises a body part and a protruding part arranged towards the input mirror, the input mirror and the protruding part form a resonant cavity, and at least one beam waist position of laser generated in the resonant cavity is positioned outside the resonant cavity under the action of the output mirror. By the mode, the method can improve the optical frequency conversion of the pulse laserAnd (5) efficiency of conversion.

Description

Pulse laser

Technical Field

The present application relates to the field of laser technology, and in particular, to a pulsed laser.

Background

In recent years, laser light has been widely used in fields such as communication, processing, medical treatment, and mapping because of its excellent directivity, coherence, high brightness, and the like. In the related art, some pulse lasers can obtain laser output of the second harmonic, the third harmonic or the fourth harmonic of pulse fundamental frequency light through extra-cavity optical frequency conversion. However, the beam waist position of the fundamental frequency laser generated by the pulse laser is located at the output mirror of the pulse laser or in the resonant cavity, the beam waist position of the fundamental frequency laser is far away from the harmonic crystal, and the frequency conversion efficiency of the pulse laser is low.

Disclosure of Invention

The embodiment of the application provides a pulse laser, which can improve the frequency conversion efficiency of the pulse laser.

The embodiment of the application provides a pulse laser. The pulse laser comprises a pumping source, a coupling lens group, an input mirror, a gain medium, a loss control device, an output mirror and at least one harmonic crystal, wherein the coupling lens group, the input mirror, the gain medium, the loss control device, the output mirror and the at least one harmonic crystal are sequentially arranged along the optical axis of the pumping source. The output mirror comprises a body part and a protruding part arranged towards the input mirror, the input mirror and the protruding part form a resonant cavity, and at least one beam waist position of laser generated in the resonant cavity is positioned outside the resonant cavity under the action of the output mirror.

The beneficial effects of this application are: on the one hand, the surface of the bulge part close to the input mirror is a convex surface, and the convex surface and the resonant cavity formed by the input mirror can improve the propagation of laser in the resonant cavity, so that the resonant cavity has a stable laser mode. On the other hand, the body portion cooperates with the convex portion to form a lens for the output mirror, and the output mirror can interfere with propagation of the fundamental laser light. After the fundamental frequency laser is output from the resonant cavity through the output mirror, the beam waist position of the fundamental frequency laser can be positioned outside the resonant cavity and is close to the harmonic crystal. Therefore, the harmonic crystal performs frequency conversion, namely the beam waist part with higher power density in the fundamental frequency laser propagation process, so that the frequency conversion efficiency of the pulse laser can be improved.

Drawings

FIG. 1 is a schematic diagram of an embodiment of a pulse laser according to the present application;

FIG. 2 is a schematic diagram of a first embodiment of an output mirror in the pulse laser of FIG. 1;

FIG. 3 is a schematic diagram of a second embodiment of an output mirror in the pulsed laser of FIG. 1;

fig. 4 is a schematic diagram of a third embodiment of an output mirror in the pulse laser of fig. 1.

Detailed Description

The following description of the technical solutions in the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

In the research process, the inventor finds that in recent years, laser has good directivity, coherence, high brightness and other characteristics, and is widely applied to the fields of communication, processing, medical treatment, mapping and the like. In the related art, some pulse lasers perform optical frequency conversion through harmonic crystals outside a resonant cavity, so that laser output of second harmonic, third harmonic or fourth harmonic of pulse fundamental frequency light can be obtained. The optical frequency conversion efficiency of the pulse laser is proportional to the power density of the fundamental frequency light, the square of the power density or the power density to the third power. That is, the higher the fundamental optical power density at the harmonic crystal, the higher the optical frequency conversion efficiency of the pulse laser. And the harmonic crystal has a certain receiving angle range, and the divergence angle of the fundamental frequency light is required to be as small as possible. The pulse laser has smaller beam diameter at the beam waist of the fundamental laser, higher fundamental laser power density, and approximately parallel beams within the rayleigh length near the beam waist. However, the beam waist position of the laser generated by the pulse laser is located at the output mirror of the pulse laser or in the resonant cavity, the beam waist position of the laser is far away from the harmonic crystal, and the frequency conversion efficiency of the pulse laser is low. In some pulse lasers, the beam waist of the laser is also displaced by arranging a plurality of optical elements in combination outside the resonant cavity, but the combination of the plurality of optical elements increases the size and the complexity of the structure of the pulse laser, which leads to an increase in cost. In order to improve the above technical problems, the present application may provide the following embodiments.

Referring to fig. 1 and 2, an embodiment of the present application provides a pulse laser 1. The pulse laser 1 includes a pump source 10, a coupling lens group 20, an input mirror 30, a gain medium 40, a loss control device 50, an output mirror 60, and at least one harmonic crystal 70, which are disposed in this order along the optical axis of the pump source 10. The output mirror 60 includes a body 61 and a protrusion 62 disposed toward the input mirror 30, the input mirror 30 and the protrusion 62 form a resonant cavity 80, and at least one beam waist of the laser light generated in the resonant cavity 80 is located outside the resonant cavity 80 under the action of the output mirror 60.

Specifically, the pump source 10 is capable of emitting pump light having a preset power and a preset wavelength, which is capable of exciting the gain medium 40 to pump the activated particles from a ground state to a high energy level to achieve population inversion. Alternatively, the pump source 10 may also employ different excitation modes and excitation means than those described above, depending on the operating conditions of the gain medium 40 and the pulsed laser 1. Such as gas discharge excitation, chemical excitation, or nuclear excitation. In one embodiment, pump source 10 is a fiber coupled output semiconductor laser, a fast axis compressed single tube semiconductor laser, or a semiconductor laser array. Optionally, the output power of the pump source 10 is 20-40W, and the wavelength of the light output by the pump source is 700-900nm. For example, the pump source 10 may be a 30W fiber coupled output semiconductor laser with 808nm, and the output fiber has a core diameter of 200 microns and N.A is 0.22.

The coupling lens group 20 can be combined with the pump source 10 into a pump system, and the coupling lens group 20 can focus the pump light so that it can be transmitted into the resonant cavity 80 and act with the gain medium 40. In one embodiment, the coupling lens group 20 is a plano-convex lens with two convex surfaces disposed opposite to each other, and the focal lengths are 10mm and 30mm, respectively.

The input mirror 30 is capable of passing the light beam after the coupling lens group 20 is applied, so that it enters the resonator 80. The input mirror 30 also prevents the fundamental light in the cavity 80 from passing out, thereby reducing leakage of the fundamental light from the cavity 80 and enabling the fundamental light to resonate within the cavity 80. In other words, the pump light may enter the cavity 80 from the side near the pump source 10 through the input mirror 30 and the side of the input mirror 30 near the gain medium 40, and the fundamental light in the cavity 80 is not allowed to pass through the side of the input mirror 30 near the gain medium 40. In one embodiment, the side of the input mirror 30 facing the pump source 10 is covered with an antireflection film, and the side of the input mirror 30 facing the output mirror 60 is covered with an antireflection film and a reflection film. For example, input mirror 30 is a bi-planar mirror, input mirror 30 produces 808nm anti-reflection film toward the plane of pump source 10, and input mirror 30 produces 808nm anti-reflection film and 1064nm highly reflective multilayer dielectric film toward the plane of output mirror 60. The anti-reflection film can facilitate the incidence of pump light into the resonant cavity 80, and the high-reflection multilayer dielectric film can reduce the reverse output of fundamental frequency light from the resonant cavity 80.

Gain medium 40 (or laser gain medium), which can be used to effect population inversion and produce fundamental laser light, is a material system for stimulated radiation amplification, and gain medium 40 can be a solid, such as a crystal or glass. The gain medium 40 may be a gas, such as an atomic gas, an ionic gas, or a molecular gas. The gain medium 40 may be a medium such as a semiconductor or a liquid. Gain medium 40 is capable of achieving a large degree of population inversion at a particular energy level of its working particles and effectively maintaining such population inversion throughout the lasing action.

In one embodiment, gain medium 40 is Nd: YAG crystal, nd: YVO ₄ Crystals, nd: gdVO ₄ Crystals, nd: YLF crystal, yb: YAG crystal or ceramic Nd: YAG. Alternatively, the gain medium 40 may employ Nd: YAG crystals. Gain medium 40 has a length of 10-15mm and a doping concentration of 0.1% -2%. For example, the gain medium 40 has a length of 12mm and a doping concentration of 0.8%, a square light transmission aperture of 3mm may be provided, and dual wavelength antireflection films of 808nm and 1064nm may be provided on the gain medium 40.

Referring to fig. 1, a loss control device 50 is further disposed between the gain medium 40 and the output mirror 60, and the loss control device 50 is used to control the quality factor of the resonant cavity 80. The quality factor, i.e., Q. The quality factor is an indicator of how good the quality of the optical cavity 80 in the pulsed laser 1 is, and is defined as 2pi×the energy stored in the cavity 80/the energy lost per oscillation period. The higher the quality factor, the lower the required pump threshold, i.e. the easier the laser is to oscillate.

The loss control device 50 adjusts the Q-factor to a lower state after the pump source 10 starts to operate, i.e. the loss control device 50 is in an "off" or "low Q" state, at which time no oscillation can form in the resonator 80, and the population inversion degree in the gain medium 40 is continuously accumulated and increased. When the population inversion reaches the maximum, the loss control device 50 increases the quality factor in a short time, that is, the loss control device 50 is in an on state or a high Q state, so that instantaneous strong fundamental frequency laser oscillation is formed in the cavity, and the energy accumulated to a higher degree of inversion population is concentrated and rapidly released in a short time interval, so that laser output with a very narrow pulse width and high peak power can be obtained, and Q-switched laser pulse output is generated and output outside the cavity.

In one embodiment, loss control device 50 is any one of an acousto-optic active Q-switch, an electro-optic active Q-switch, or a saturable absorber passive Q-switch.

Specifically, the acousto-optic active Q switch is used for completing the Q-switching task by utilizing the Bragg diffraction principle of an acousto-optic device. The acousto-optic active Q-switch is comprised of an acousto-optic interactive medium (e.g., fused silica) and a transducer bonded thereto. The transducer converts the high frequency signal into ultrasonic waves. The acousto-optic active Q-switch is inserted into the resonant cavity 80, so that higher diffraction loss can be generated, and the resonant cavity 80 has a lower quality factor, and the acousto-optic active Q-switch is in an off state. When a large number of particles are accumulated in the high energy level of the laser, the ultrasonic wave is removed, the diffraction effect disappears, the loss is reduced, and the acousto-optic active Q switch is in an on state, so that pulse laser is formed.

The electro-optical active Q-switch utilizes the electro-optical effect of the crystal, and adds a step voltage on the crystal to adjust the emission loss of photons in the cavity. When the electro-optical active Q switch works, voltage is applied to the two ends of the crystal, the loss of the resonant cavity 80 is large due to the polarization effect of the crystal, the quality factor is low, laser does not oscillate, the energy level of the laser continuously accumulates the particle number, and the electro-optical active Q switch is in a closed state. After the reversed particle number is accumulated to a certain degree, the voltages at the two ends of the crystal are removed, the resonant cavity 80 is suddenly changed to have low loss and high quality factor, and the electro-optical active Q switch is in an on state to form pulse laser.

The saturable absorber Q-switch belongs to a passive Q-switch. A saturable absorbing dye box or a color center crystal and other absorbing materials are placed in the resonant cavity 80. The laser transmissivity of the absorbing material to the interior of the cavity 80 is a function of the light intensity. At the beginning, the intensity of the stimulated radiation within the cavity 80 is low and the absorption of the optical radiation by the absorbing material is large, i.e. the quality factor of the cavity 80 is low. When gain medium 40 is sufficiently pumped to reach the lasing threshold, the absorption material undergoes saturated absorption, the transmittance rises, and the quality factor of cavity 80 rises to a higher value, thereby forming a pulsed laser.

Referring to fig. 1, a resonant cavity 80 is formed between the output mirror 60 and the input mirror 30. The length of the resonant cavity 80 (the distance between the output mirror 60 and the input mirror 30) may be between 50-100mm, for example 60mm or 65mm. The output mirror 60 includes a body portion 61 and a convex portion 62 protruding toward the input mirror 30, the input mirror 30 and the convex portion 62 constitute a resonant cavity 80, and at least one of beam waist positions of laser light generated in the resonant cavity 80 is located outside the resonant cavity 80 in the direction of the output mirror 60 by the output mirror 60. The convex portion 62 is covered with a partial reflection film on the side facing the input mirror 30, and the body portion 61 is covered with an antireflection film on the side facing the harmonic crystal 70. The reflective film covering the boss 62 has the ability to partially reflect light and partially transmit light. The reflection film can reflect part of the fundamental frequency laser light in the resonator 80, and the light can repeatedly oscillate in the resonator 80 by the cooperation of the reflection film and the input mirror 30, thereby accumulating the number of particles. A part of the fundamental laser light oscillating within the resonator 80 can pass through the reflective film and be transmitted out of the resonator 80. The antireflection film covered by the body portion 61 toward the harmonic crystal 70 can increase transmission of the fundamental laser light to improve the light emission efficiency of the pulse laser 1. The surface of the boss 62 near the input mirror 60 is a curved surface, and the curved surface and the resonant cavity 80 formed by the input mirror 30 can improve the propagation of laser in the resonant cavity 80, so that the resonant cavity 80 has a stable laser mode. On the other hand, the body portion 61 and the convex portion 62 cooperate to allow the lens formed by the output mirror 60 to interfere with the propagation of the fundamental laser light. After the fundamental laser light passes from the cavity 80 through the output mirror 60, at least one of the beam waist positions of the fundamental laser light can be located outside the cavity 80 in the direction of the output mirror 60 and in close proximity to the harmonic crystal 70. In this way, since the harmonic crystal 70 frequency-converts the beam waist portion having a high power density in the fundamental laser propagation, the frequency conversion efficiency of the pulse laser 1 can be improved.

In one embodiment, referring to fig. 3, the body 61 is provided with a protrusion 63 on a side facing the harmonic crystal 70, and an antireflection film is laminated on a side of the protrusion 63 facing the harmonic crystal 70. The output mirror 60 composed of the main body 61 and the convex portion 62 can change the beam waist position of the fundamental laser beam. The provision of the projection 63 enables the focal length of the output mirror 60 to be changed, thereby enabling the beam waist position of the fundamental frequency laser light to be further changed to improve the frequency conversion efficiency of the pulse laser 1. The antireflection film can increase the transmission of the fundamental laser light to improve the light emission efficiency of the pulse laser 1.

In another embodiment, the body portion 61 is concavely provided toward one face of the harmonic crystal 70 and formed with a concave surface covered with an antireflection film. Wherein the concavity of the body portion 61 and the convexity of the convexity 62 can form a lens, and the degree of convexity of the convexity 62 (or the curvature of the surface of the convexity 62) and the depth of concavity of the body portion 61 (or the curvature of the surface of concavity) can affect the ability of the output mirror 60 to change the optical path, respectively. The cooperation between the concave and convex portions 62 of the body portion 61 can make the output mirror 60 have a proper focal length, so that the beam waist position of the fundamental laser light is matched with the position of the harmonic crystal 70, to further improve the frequency conversion efficiency of the pulse laser 1.

The output mirror 60 is provided with a first harmonic crystal 71 and a second harmonic crystal 72 on a side thereof away from the input mirror 30, the first harmonic crystal 71 being a second harmonic crystal, and the second harmonic crystal 72 being either a third harmonic crystal or a fourth harmonic crystal. After the fundamental laser light irradiates the harmonic crystal 70, nonlinear frequency conversion can be generated, so that frequency conversion of the fundamental laser light is realized. The first harmonic crystal 71 and the second harmonic crystal 72 are different types of harmonic crystals 70, and after the first harmonic crystal 71 frequency-converts the fundamental frequency laser light, the second harmonic crystal 72 can further frequency-convert the second harmonic laser light converted by the first harmonic crystal 71 and the residual fundamental frequency light transmitted through the first harmonic crystal 71. The first harmonic crystal 71 and the second harmonic crystal 72 cooperate to enable the pulse laser 1 to output laser light of a corresponding frequency.

In an embodiment, the beam waist position of the laser generated in the resonant cavity 80 is located between the first harmonic crystal 71 and the second harmonic crystal 72 under the action of the output mirror 60, so that the beam waist position of the fundamental laser has a shorter distance from both the first harmonic crystal 71 and the second harmonic crystal 72, thereby improving the frequency conversion efficiency.

Further, since the first harmonic crystal 71 and the second harmonic crystal 72 have different optical frequency conversion efficiencies, in order to improve the optical frequency conversion efficiency of the pulse laser 1 as a whole, in an embodiment, for example, the optical frequency conversion efficiency of the first harmonic crystal 71 is greater than that of the second harmonic crystal 72, the beam waist is located close to the second harmonic crystal 72. Or the optical frequency conversion efficiency of the second harmonic crystal 72 is greater than that of the first harmonic crystal 71, the beam waist is positioned close to the first harmonic crystal 71. By doing so, the beam waist position of the fundamental laser light can be made closer to the less efficient one of the first harmonic crystal 71 and the second harmonic crystal 72. This can compensate for the lower efficiency of the harmonic crystal 70 itself by the location of the laser beam waist.

In the technology of the above embodiment, the second harmonic crystal is LBO crystal, biBO crystal, BBO crystal, KTP crystal, PPKTP crystal, PPLT crystal, mgO: PPLT crystals, PPSLT crystals or MgO: any one of SPPLT crystals, the third harmonic crystal is any one of LBO crystals, biBO crystals, BBO crystals or CLBO crystals, and the fourth harmonic crystal is any one of BBO crystals or CLBO crystals. The specific limitation is not particularly restricted.

The foregoing is only examples of the present application, and is not intended to limit the scope of the patent application, and all equivalent structures or equivalent processes using the descriptions and the contents of the present application or other related technical fields are included in the scope of the patent application.

Claims

1. A pulsed laser, comprising: the device comprises a pumping source, a coupling lens group, an input mirror, a gain medium, a loss control device, an output mirror and at least one harmonic crystal, wherein the coupling lens group, the input mirror, the gain medium, the loss control device, the output mirror and the at least one harmonic crystal are sequentially arranged along an optical axis of the pumping source; the output mirror comprises a body part and a protruding part arranged towards the input mirror, the input mirror and the protruding part form a resonant cavity, and the loss control device is used for adjusting the quality factor of the resonant cavity; at least one beam waist position of the laser generated in the resonant cavity is positioned outside the resonant cavity under the action of the output mirror.

2. The pulsed laser of claim 1, wherein:

one surface of the input mirror facing the pumping source is covered with an antireflection film, one surface of the input mirror facing the output mirror is covered with an antireflection film and a reflection film in a lamination mode, one surface of the protruding part of the output mirror facing the input mirror is covered with a partial reflection film, and one surface of the body part of the output mirror facing the harmonic crystal is covered with an antireflection film.

3. The pulsed laser of claim 1, wherein:

the loss control device is any one of an acousto-optic active Q switch, an electro-optic active Q switch or a saturable absorber passive Q switch.

4. The pulsed laser of claim 1, wherein:

the gain medium is Nd: YAG crystal, nd: YVO ₄ Crystals, nd: gdVO ₄ Crystals, nd: YLF crystal, yb: YAG crystal or ceramic Nd: YAG.

5. The pulsed laser of claim 1, wherein:

the output mirror is far away from one side of the input mirror and is provided with a first harmonic crystal and a second harmonic crystal, wherein the first harmonic crystal is a second harmonic crystal, and the second harmonic crystal is any one of a third harmonic crystal and a fourth harmonic crystal.

6. The pulsed laser of claim 5, wherein:

the second harmonic crystal is KTP crystal, LBO crystal, biBO crystal, BBO crystal, PPLT crystal, mgO: PPLT crystals, PPKTP crystals, PPSLT crystals, or MgO: any one of SPPLT crystals, the third harmonic crystal is any one of LBO crystals, biBO crystals, BBO crystals or CLBO crystals, and the fourth harmonic crystal is any one of BBO crystals or CLBO crystals.

7. The pulsed laser of claim 5, wherein:

at least one beam waist position of the laser is located between the first harmonic crystal and the second harmonic crystal under the action of the output mirror;

the optical frequency conversion efficiency of the first harmonic crystal is greater than that of the second harmonic crystal, and the beam waist is close to the second harmonic crystal;

alternatively, the second harmonic crystal has an optical frequency conversion efficiency greater than that of the first harmonic crystal, and the beam waist is positioned near the first harmonic crystal.

8. The pulsed laser of claim 1, wherein:

the body portion is towards harmonic crystal one side is equipped with the bulge, the bulge towards one side lamination of harmonic crystal is covered with the antireflection coating.

9. The pulsed laser of claim 1, wherein:

the body part is concavely arranged towards one surface of the harmonic crystal and is provided with a concave surface, and the concave surface is covered with an antireflection film.

10. The pulsed laser of claim 1, wherein:

the output power of the pumping source is 20-40W, the wavelength of light output by the pumping source is 700-900nm, the length of the gain medium is 10-15mm, and the doping concentration is 0.1% -2%; the length of the resonant cavity is 50-100mm.