High repetition frequency pulse laser based on intracavity polycrystal tandem connection

Abstract

The invention relates to a high repetition frequency pulse laser based on intracavity polycrystal tandem connection, which comprises a pumping source, a first 45-degree reflecting mirror, a plurality of crystals connected in series by a light path, an output coupling mirror, a Q-switching unit and a total reflection mirror which are sequentially arranged along another light path reflected by the first 45-degree reflecting mirror, and a power supply unit, the power supply unit supplies power to the semiconductor laser and the Q-switching unit. An intracavity polycrystal tandem connection technology is adopted, high absorption of pump light is guaranteed, heat on a single laser crystal is dispersed, and the adverse effect of the thermal effect of the laser is reduced; meanwhile, the Q-modulation technology is utilized to obtain the high-repetition-frequency laser, the light-to-light conversion efficiency and the long-term operation reliability of the laser are effectively improved, and the output of the high-repetition-frequency pulse laser with higher power and better light beam quality is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of solid lasers, and more specifically, relates to a high repetition rate pulse laser based on intracavity polycrystal series connection. Background Art

[0002] Laser diode pumped solid pulse lasers have the advantages of high conversion efficiency, good beam quality, high repetition rate, and compact structure. They are widely used in many fields such as laser radar, laser ranging, laser precision processing, space optical communication, and medicine. With the rapid development of Q-switching technology and the continuous improvement of crystal material performance, the output parameters of laser diode pumped solid pulse lasers are constantly optimized, which can achieve the high repetition rate and narrow pulse width laser output required by airborne platforms, but still face the problem of thermal effect management under high-power pumping. Since solid laser media inevitably produce thermal effects such as thermal gradient, thermal stress, thermal lens, thermally induced birefringence, and thermal depolarization after absorbing pump energy, the increase in pump power will significantly increase the thermal effect of the laser medium, resulting in reduced laser output power and stability, and poor beam quality. In airborne environments, this effect will become more serious, greatly limiting the improvement of laser output performance. Although the CN202210441350 patent "A Compact Airborne Wide-Temperature Solid-State Laser" uses a laser diode array to side-pump the laser slab crystal, enhances heat dissipation through an integrated heat sink design, uses a high-precision temperature control unit to effectively control the temperature of the laser crystal and the pump source, and uses a double-orthogonal Porro prism combined polarization output cavity type to improve the solid-state laser light source's ability to resist airborne vibration and cavity mirror detuning caused by a wide temperature environment, most lasers using this cavity type can only output pulsed laser outputs with a repetition frequency of less than 1kHz due to large intra-cavity losses, and are not suitable for high-repetition-rate pulsed laser outputs. Summary of the invention

[0003] In view of the problem that the existing high repetition rate pulse lasers have limited output power and poor output beam quality due to the thermal effect of the laser medium under high-power pumping and other reasons, the thermal effect improvement method used is difficult to achieve high beam quality and high power output while maintaining the miniaturization of the overall structure of the laser, which limits the application of high repetition rate pulse lasers in airborne platforms. The present invention proposes a high repetition rate pulse laser based on intracavity multi-crystal series connection.

[0004] The technical solution of the present invention is as follows:

[0005] A high repetition rate pulse laser based on multiple crystals connected in series in a cavity comprises a pump source arranged in sequence along an optical path, a first 45° reflector, a plurality of crystals connected in series by the optical path, an output coupling mirror, and a Q-switching unit and a total reflector arranged in sequence along another optical path after reflection by the first 45° reflector, and also comprises a power supply unit, which supplies power to the semiconductor laser and the Q-switching unit.

[0006] In some embodiments, the Q-switching unit includes a polarizer and a Q-switching crystal arranged in sequence along the optical path, or the Q-switching unit includes a polarizer, a quarter wave plate, and a Q-switching crystal arranged in sequence along the optical path.

[0007] In some embodiments, the multiple crystals connected in series by the optical path include a first laser crystal and a second laser crystal, both of which are coated with a high-transmittance film for pump light and 1064nm laser, are wrapped in indium foil in a copper heat sink, and use a thermoelectric cooler TEC and an air-cooled radiator to achieve high-precision temperature control.

[0008] In some embodiments, the pump source includes a semiconductor laser, an optical fiber, and a pump light coupling unit sequentially arranged along an optical path, and the pump source is a single-end or double-end pump.

[0009] In some embodiments, the pump light coupling unit includes a collimating lens and a focusing lens sequentially arranged along the optical path.

[0010] In some embodiments, the semiconductor laser is a semiconductor laser with a maximum continuous output power of 70W and a central wavelength of 808nm; the collimating lens and the focusing lens are both plano-convex lenses, and their focal length ratio is 1:4.5.

[0011] In some embodiments, a second 45° reflector is further included, which is disposed along the optical path between the crystal and the output coupling mirror. The light emitted from the crystal enters the second 45° reflector and then enters the output coupling mirror to emit laser light.

[0012] In some embodiments, the first 45° reflector and the second 45° reflector are both coated with a film that is highly transparent to pump light and highly reflective to 1064nm laser.

[0013] The high repetition rate pulse laser based on intracavity polycrystal series connection of the present invention has the following advantages:

[0014] The intracavity multi-crystal series connection technology is adopted to ensure high absorption of pump light while dispersing the heat on a single laser crystal, reducing the adverse effects of thermal effects of the laser; at the same time, the Q-switching technology is used to obtain high repetition rate lasers, effectively improving the light-to-light conversion efficiency and the long-term operation reliability of the laser, and achieving the output of high-repetition rate pulsed lasers with higher power and better beam quality. In the embodiment, a second 45° reflector is arranged along the optical path between the crystal and the output coupling mirror. After the light emitted from the crystal enters the second 45° reflector, it enters the output coupling mirror to emit the laser. This U-shaped resonant cavity structure, through the reasonable design of the coupling lens group and the use of a reflector to fold the optical path, enables the single-ended pump light to be collimated and focused by the coupling lens group. The light beam can be well matched with the oscillating light in multiple crystals, ensuring the high efficiency of pump light conversion while saving space and volume, and the structure is more compact. In short, an effective way is provided for obtaining high beam quality and high repetition rate airborne lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of the high repetition rate pulse laser of the present invention;

[0016] Figure 2 This is a diagram showing the spot distribution of the high repetition rate pulse laser of the present invention when the output energy is 2 mJ.

[0017] In the figure, 1-semiconductor laser, 2-optical fiber, 3-collimating lens, 4-focusing lens, 5-first 45° reflector, 8-second 45° reflector, 6-first laser crystal, 7-second laser crystal, 9-polarizer, 10-quarter wave plate, 11-electro-optic Q-switched crystal, 12-total reflector, 13-planar partial reflector, 1416-power supply unit, 14-power supply control system, 15-pump drive power supply, 16-electro-optic Q-switched drive power supply, and the direction of the arrow in the figure is the light output direction of the high repetition rate pulse laser. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation methods. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the implementation methods of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0019] like Figure 1As shown, the present invention is based on a high repetition rate pulse laser with multiple crystals connected in series in the cavity, including a pump source arranged in sequence along the optical path, a first 45° reflector, a plurality of crystals connected in series by the optical path, an output coupling mirror, and a Q-switching unit and a total reflector arranged in sequence along another optical path after reflection by the first 45° reflector, and also includes a power supply unit, which supplies power to the semiconductor laser and the Q-switching unit. The output coupling mirror is a plane partial reflector, specifically a half-reflector; the Q-switching unit includes a polarizer and a Q-switching crystal arranged in sequence along the optical path, and the working mode is depressurization at this time; in this embodiment, the Q-switching unit includes a polarizer, a quarter-wave plate and a Q-switching crystal arranged in sequence along the optical path, and the working mode is boosting at this time. The plurality of crystals connected in series by the optical path include a first laser crystal and a second laser crystal, and the first laser crystal and the second laser crystal are both coated with a high-transmittance film for pump light and 1064nm laser, and are wrapped in a copper heat sink by indium foil, and high-precision temperature control is achieved by using a thermoelectric cooler TEC and an air-cooled radiator. In some optional embodiments, the number of crystals connected in series by the optical path can be one or three, depending on the actual use requirements. The purpose is to produce large energy. The greater the energy required, the more crystals will be considered to be connected in series. If the required energy is small, only one crystal is needed. The pump source includes a semiconductor laser and a pump light coupling unit arranged in sequence along the optical path; in this embodiment, the pump source includes a semiconductor laser, an optical fiber, and a pump light coupling unit arranged in sequence along the optical path, and the pump source is single-ended; in some optional embodiments, the pump source is double-ended pumping; specifically, the pump light coupling unit includes a collimating lens and a focusing lens arranged in sequence along the optical path, and the semiconductor laser is a semiconductor laser with a maximum continuous output power of 70W and a central wavelength of 808nm; the collimating lens and the focusing lens are both plano-convex lenses, and their focal length ratio is 1:4. 5; In this embodiment, it also includes a second 45° reflector arranged between the crystal and the output coupling mirror along the optical path. After the light emitted from the second laser crystal enters the second 45° reflector, it enters the output coupling mirror to emit laser. The total reflection mirror, the first 45° reflector, the second 45° reflector and the output coupling mirror constitute a "U"-shaped resonant cavity. From the total reflection mirror along the optical path to the output coupling mirror (planar partial reflector) are the electro-optical Q-switched crystal, the quarter wave plate, the polarizer, the first 45° reflector, the first laser crystal, the second laser crystal and the second 45° reflector.

[0020] The power supply unit is composed of a power supply control system, a pump drive power supply and a Q-switched drive power supply. The power supply control system is connected to the pump drive power supply and the Q-switched drive power supply. The pump drive power supply is connected to the semiconductor laser and is also connected to the trigger signal input end of the Q-switched drive power supply. The output end of the Q-switched drive power supply is connected to the input end of the Q-switched crystal. The Q-switched crystal can be an electro-optical Q-switched crystal or an acousto-optical Q-switched crystal.

[0021] The control process of the circuit control system is as follows: the power supply control system performs unified power supply control on the pump drive power supply and the electro-optical Q-switching drive power supply. After receiving the power supply signal, the pump drive power supply pumps the semiconductor laser and sends a trigger signal to the electro-optical Q-switching drive power supply. After receiving the power supply signal and the trigger signal, the electro-optical Q-switching drive power supply provides voltage to the electro-optical Q-switching crystal, and the laser then outputs Q-switched pulse laser. The input mirror, the first 45° reflector and the second 45° reflector are all coated with a high-transmittance film for pump light and a high-reflection film for 1064nm laser. The output coupling mirror is a flat partial reflector, which is coated with a partial high-reflection film for 1064nm laser. The collimating lens and the focusing lens are coated with a high-transmittance film for pump light, forming a coupling lens group to collimate and focus the pump light output by the semiconductor laser into the laser crystal. The first laser crystal and the second laser crystal are both coated with a high-transmittance film for pump light and 1064nm laser, wrapped in a copper heat sink by indium foil, and use a thermoelectric cooler (TEC) and an air-cooled radiator to achieve high-precision temperature control. The polarizer is a 56° polarizer or a 45° polarizer or a PBS prism, which has high reflection of the S polarized light of the 1064nm oscillating laser in the resonant cavity and high transmission of the P polarized light, and the polarization extinction ratio is greater than 500:1. The electro-optical Q-switched crystal, the quarter-wave plate and the polarizer constitute an electro-optical Q-switched switch. The power supply control system sends a power supply signal to the pump driving power supply, and the pump driving power supply pumps the semiconductor laser after receiving the power supply signal. The pump light output by the semiconductor laser passes through the collimating lens, the focusing lens, and the first 45° reflector to pump the first laser crystal and the second laser crystal. The spontaneous radiation light generated by the laser crystal passes through the second 45° reflector and the coupling output mirror, and then passes through the dual laser crystal after reflection again, and then passes through the first 45° reflector, and is transmitted by the polarizer to obtain a laser in the P polarization direction. When no voltage is applied to the electro-optic Q-switched crystal, the quarter-wave plate is rotated so that the laser light in the P-polarization direction passes through the quarter-wave plate and the electro-optic Q-switched crystal twice, and then its polarization state becomes the S-polarization direction. It is reflected out of the resonant cavity by the polarizer, and the resonant cavity is in a high-loss state and cannot oscillate, so the Q switch is closed. When voltage is applied to the electro-optic Q-switched crystal, the polarization state of the laser light is still the P-polarization direction. After passing through the polarizer, it forms oscillations between the input mirror and the coupling output mirror, and the Q switch is opened to generate a Q-switched pulse output.

[0022] In combination with specific component parameters, two specific design examples of the high repetition rate pulse laser based on the intracavity polycrystal series connection of the present invention are further given below.

[0023] The semiconductor laser has a maximum continuous output power of 70W and a central wavelength of 808nm, a core diameter of 200μm, and a numerical aperture of 0.22. The collimating lens and focusing lens 4 of the pump light coupling unit are both plano-convex lenses, and their focal length ratio is 1:4.5. The total reflection mirror is a 0° total reflection mirror coated with a high transmission film of 808nm (T>95%) and a high reflection film of 1064nm (R>99.5%), and the size is Φ12.7mm*3mm. The first laser crystal 5 and the second laser crystal 6 are both Nd:YAG crystals, with a doping concentration of 0.2at.%, and a square rod structure of 3mm*3mm*30mm is selected. It is wrapped with indium foil and placed in a cooling heat sink. A thermoelectric cooler (TEC) is used to control the temperature of the cooling heat sink at 25°C. The first 45° reflector 5 and the second 45° reflector 8 are both coated with a 808nm high transmittance film (T>95%) and a 1064nm high reflectance film (R>99.5%).

[0024] The output coupling mirror is a planar partial reflector, a half-reflector, with a size of Φ12.7mm*3mm, coated with a 1064nm semi-transmissive and semi-reflective film (T=50%). The length of the "U"-shaped resonant cavity formed by the input mirror 12, the first 45° reflector 5, the second 45° reflector 8 and the output coupling mirror 13 is about 245mm.

[0025] The electro-optical Q-switched crystal 11 is a pair of orthogonal rubidium titanyl phosphate (RTP) crystals with a size of 3mm*3mm*14mm. The polarizer 9 is a 56° polarizer coated with a 1064nm S-polarized light high reflection film (R>99.8%) and a P-polarized light high transmission film (T>98%). The electro-optical Q-switched crystal 11, the quarter-wave plate 10 and the polarizer 9 constitute an electro-optical Q-switched switch. By periodically applying a voltage of about 1300V to the electro-optical Q-switched crystal 11, a laser output with a repetition frequency of 10kHz, a pulse width of about 10ns, a pulse energy of 2mJ, and a corresponding peak power of about 200kW is obtained. The beam quality M of the output laser is measured by a beam quality analyzer. 2 x=1.834,M 2 y = 1.904, the light-to-light conversion efficiency is 28.5%, see Figure 2 , the measured spot distribution under the output energy of 2mJ.

Claims

1. A high repetition rate pulse laser based on intracavity polycrystalline series connection, characterized in that: The invention comprises a pump source, a first 45° reflector, a plurality of crystals connected in series by the optical path, an output coupling mirror, and a Q-switching unit and a total reflection mirror arranged in sequence along another optical path after being reflected by the first 45° reflector. The invention also comprises a power supply unit, which supplies power to the semiconductor laser and the Q-switching unit.

2. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 1 is characterized in that: The Q-switching unit includes a polarizing plate and a Q-switching crystal arranged in sequence along the light path, or the Q-switching unit includes a polarizing plate, a quarter wave plate and a Q-switching crystal arranged in sequence along the light path.

3. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 1 or 2, characterized in that: The multiple crystals connected in series by the optical path include a first laser crystal and a second laser crystal. Both the first laser crystal and the second laser crystal are coated with a high-transmittance film for pump light and 1064nm laser, are wrapped in indium foil in a copper heat sink, and use a thermoelectric cooler TEC and an air-cooled radiator to achieve high-precision temperature control.

4. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 3 is characterized in that: The pump source comprises a semiconductor laser, an optical fiber, and a pump light coupling unit which are sequentially arranged along an optical path. The pump source is a single-end or double-end pump.

5. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to any one of claim 4, characterized in that: The pump light coupling unit comprises a collimating lens and a focusing lens which are sequentially arranged along the optical path.

6. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 5, characterized in that: The semiconductor laser has a maximum continuous output power of 70W and a central wavelength of 808nm; the collimating lens and focusing lens are both plano-convex lenses, and their focal length ratio is 1:4.

5.

7. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 1, characterized in that: It also includes a second 45° reflector disposed between the crystal and the output coupling mirror along the optical path. The light emitted from the crystal enters the second 45° reflector and then enters the output coupling mirror to emit laser light.

8. The high repetition rate pulse laser based on intracavity polycrystalline series connection according to claim 7, characterized in that: The first 45° reflector and the second 45° reflector are both coated with a film that is highly transparent to pump light and highly reflective to 1064nm laser.

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