阅读说明：本技术 一种高效率的棒状激光放大器及其工作方法 (High-efficiency rod-shaped laser amplifier and working method thereof ) 是由 焦中兴 何秋润 张宝夫 于 2020-12-07 设计创作，主要内容包括：本发明公开一种高效率的棒状激光放大器及工作方法,包括脉冲种子源、隔离调节单元、双程放大器主体和泵浦耦合控制单元,所述脉冲种子源出射激光依次经过隔离调节单元和双程放大器主体,所述隔离调节单元沿出射激光前进方向依次包括隔离器、第一半波片和第一透镜,所述双程放大器主体沿出射激光前进方向依次包括偏振分束器、45°法拉第旋转器、第二半波片、第一反射镜、增益介质、第二透镜和第三反射镜,所述泵浦耦合控制单元包括激光二极管、耦合透镜组和驱动电源。本发明是一种结构简单、泵浦转换效率高、输出光斑圆度高、光束质量好的棒状激光放大器。本发明作为一种高效率的棒状激光放大器及其工作方法,可广泛应用于固体激光放大技术领域。(The invention discloses a high-efficiency rod-shaped laser amplifier and a working method thereof, and the high-efficiency rod-shaped laser amplifier comprises a pulse seed source, an isolation adjusting unit, a double-pass amplifier main body and a pumping coupling control unit, wherein laser emitted by the pulse seed source sequentially passes through the isolation adjusting unit and the double-pass amplifier main body, the isolation adjusting unit sequentially comprises an isolator, a first half-wave plate and a first lens along the advancing direction of the emitted laser, the double-pass amplifier main body sequentially comprises a polarization beam splitter, a 45-degree Faraday rotator, a second half-wave plate, a first reflector, a gain medium, a second lens and a third reflector along the advancing direction of the emitted laser, and the pumping coupling control unit comprises a laser diode, a coupling lens group and a driving power supply. The rod-shaped laser amplifier has the advantages of simple structure, high pumping conversion efficiency, high roundness of output light spots and good light beam quality. The high-efficiency rod-shaped laser amplifier and the working method thereof can be widely applied to the technical field of solid laser amplification.)

1. The utility model provides a high-efficiency bar-shaped laser amplifier, its characterized in that includes pulse seed source, isolation regulating unit, double-pass amplifier main part and pumping coupling control unit, pulse seed source outgoing laser is through isolation regulating unit and double-pass amplifier main part in proper order, pumping coupling control unit provides the pumping energy, isolation regulating unit includes isolator, first half wave plate and first lens along outgoing laser advancing direction in proper order, double-pass amplifier main part includes polarization beam splitter, 45 Faraday rotator, second half wave plate, first speculum, gain medium, second lens and third speculum along outgoing laser advancing direction in proper order, pumping coupling control unit includes laser diode, coupling lens group and drive power supply.

2. The high efficiency rod laser amplifier of claim 1, wherein the isolation adjustment unit further comprises a filter disposed between the isolator and the pulse seed source.

3. The rod laser amplifier as defined in claim 2, wherein the second lens is a convex lens, and the distance between the second lens and the third reflector and the distance between the second lens and the exit end surface of the gain medium are both equal to the focal length of the second lens.

4. A high efficiency rod laser amplifier as defined in claim 3, wherein the double pass amplifier body further comprises a second mirror, the second mirror being disposed between the gain medium and the second lens.

5. The rod laser amplifier of claim 4, wherein the first and second mirrors are both high reflectivity for seed laser wavelength and high transmittance for pump light wavelength.

6. A method of operating a high efficiency rod laser amplifier, comprising:

the laser emitted by the pulse seed source sequentially passes through an optical filter, an isolator, a first half-wave plate, a first lens, a polarization beam splitter, a 45-degree Faraday rotator, a second half-wave plate, a first reflector, a gain medium, a second reflector, a second convex lens and a third reflector;

the laser diode is used as a pumping source, is output by the coupling optical fiber and then enters the coupling lens group, and vertically enters the end face of the gain medium after penetrating through the first reflector;

the optical filter is used for filtering other components except the central wavelength of the emergent laser;

the isolator only allows the laser to pass through in a single direction and is used for preventing the backward returning light from damaging the pulse seed source and an optical path system thereof;

the first half-wave plate is used for adjusting the polarization angle of the linear polarization seed light so that the linear polarization seed light can completely penetrate through the polarization beam splitter;

the first lens is used for adjusting the radius of a light spot of seed laser entering a gain medium to be 300 mu m;

the 45-degree Faraday rotator is used for rotating the polarization direction of the laser by 45 degrees;

the second half-wave plate is used for adjusting the polarization angle of the laser before the laser enters the gain medium;

the first reflector is used for reflecting the seed laser and transmitting the pump light to enter the gain medium;

the coupling lens group is used for adjusting the pump light;

the driving power supply is used for adjusting the working current of the laser diode.

7. The method as claimed in claim 6, wherein the driving power source controls the laser diode to emit pumping pulses with the same repetition rate as the seed laser.

8. The method as claimed in claim 7, wherein the ratio of the size of the seed spot to the size of the pump spot is greater than 1 during the amplification of the gain medium.

Technical Field

The invention belongs to the technical field of solid laser amplification, and particularly relates to a high-efficiency rod-shaped laser amplifier and a working method thereof.

Background

The Main Oscillation Power Amplification (MOPA) is a commonly used amplifier structure, uses laser with high beam quality and low pulse energy as a seed source, and designs a relatively independent single-stage or multi-stage amplifier for traveling wave amplification to realize high-energy and high-beam quality output. Thermal effects are important factors that limit the performance of the amplifier, affecting beam quality and pump extraction efficiency. In order to improve the heat dissipation capability, people design the gain medium into structures such as a slab, a slice, a planar waveguide and the like, but compared with the traditional rod-shaped gain medium, the special structure medium generally has higher processing difficulty, and individually causes the problems of complex optical path adjustment, transverse parasitic oscillation, poor beam roundness and the like, and needs shaping. Generally, the pumping energy capable of being extracted by single-pass amplification is low, and in order to improve the energy extraction efficiency, a multi-pass amplification system allowing the seed light to pass through for multiple times can be designed, but the multi-pass amplification system can increase the complexity of the system and is not favorable for long-term stable use.

Disclosure of Invention

In order to solve the above technical problems, an object of the present invention is to provide a high efficiency rod laser amplifier and a working method thereof, which have the advantages of simple and stable structure, high pump conversion efficiency, high output spot roundness, and good beam quality.

The first technical scheme adopted by the invention is as follows: the utility model provides a high-efficiency bar-shaped laser amplifier, includes pulse seed source, isolation regulating element, double-pass amplifier main part and pumping coupling control unit, pulse seed source outgoing laser passes through isolation regulating element and double-pass amplifier main part in proper order, pumping coupling control unit provides the pumping energy, isolation regulating element includes isolator, first half wave plate and first lens in proper order along outgoing laser advancing direction, double-pass amplifier main part includes polarization beam splitter, 45 Faraday rotator, second half wave plate, first speculum, gain medium, second lens and third speculum in proper order along outgoing laser advancing direction, pumping coupling control unit includes laser diode, coupling lens group and drive power supply.

The isolation adjusting unit sequentially comprises an optical filter, an isolator, a first half-wave plate and a first lens along the direction of pulse laser emitted by the pulse seed source; optionally, the filter is used to filter out other wavelength components (such as pump light in the seed laser) that may be present in the seed laser; the isolator is used for preventing possible backward reflected light from returning to the seed laser to cause damage; the first half-wave plate is used for adjusting the polarization angle of the seed laser; the first convex lens is used for adjusting the size of a light spot of seed laser when the gain medium is amplified, so that the seed laser has higher intensity to efficiently extract pumping energy, and enough redundancy can be provided to prevent the amplified laser from exceeding a damage threshold of the gain medium.

The double-pass amplification structure body sequentially comprises a polarization beam splitter, a 45-degree Faraday rotator, a second half-wave plate, a first reflector, a gain medium, a second reflector, a second lens and a third reflector; the second half-wave plate is used for adjusting the polarization direction of the seed laser; the first reflector and the second reflector have high reflectivity to seed laser wavelength and high transmittance to pump laser wavelength; the gain medium is a rod-shaped laser crystal, and seed laser enters the gain medium after passing through the first reflector to complete first-pass amplification; the second convex lens and the third reflector form an optical 4f system; after the amplified laser passes through the second reflector, the second convex lens and the third reflector, the amplified laser returns to the gain medium in the original path to complete second-pass amplification, and is finally reflected and output by the polarization beam splitter.

The pumping coupling control unit comprises a laser diode, a coupling lens group and a driving power supply; the laser diode is used as a pumping source, the output wavelength of the laser diode is positioned in an absorption peak of the gain medium, the laser diode enters the coupling lens group after being output by the coupling optical fiber, the laser diode vertically enters the end face of the gain medium after penetrating through the first reflector, and the focal point of pumping light is positioned in the gain medium; the coupling lens group is used for adjusting the pump light to enable the pump light to be matched with the seed light spot in the gain medium; preferably, the ratio of the size of the seed light spot to the size of the pumping light spot is greater than 1 (the size of the seed light spot is defined as the radius of the light spot when the seed laser is firstly incident to the end face of the gain medium, and the pumping light spot is defined as the radius of the light spot of the pumping light waist after the coupling lens group focuses on the seed laser); the driving power supply is used for adjusting the working current of the laser diode and controlling the characteristics of peak power, repetition frequency, pulse width, time delay and the like of pump light emitted by the laser diode.

Further, the isolation adjusting unit further comprises an optical filter, and the optical filter is arranged between the isolator and the pulse seed source.

Further, the second lens is a convex lens, and the distance between the second lens and the third reflector and the distance between the second lens and the exit end face of the gain medium are both equal to the focal length of the second lens.

Further, the two-way amplifier body further comprises a second mirror disposed between the gain medium and the third lens.

Further, the first mirror and the second mirror are both mirrors having high reflectivity for the seed laser wavelength and high transmittance for the pump light wavelength.

The second technical scheme adopted by the invention is as follows: a method for operating a high efficiency rod laser amplifier, comprising:

the laser emitted by the pulse seed source sequentially passes through an optical filter, an isolator, a first half-wave plate, a first lens, a polarization beam splitter, a 45-degree Faraday rotator, a second half-wave plate, a first reflector, a gain medium, a second reflector, a second convex lens and a third reflector;

the laser diode is used as a pumping source, is output by the coupling optical fiber and then enters the coupling lens group, and vertically enters the end face of the gain medium after penetrating through the first reflector;

the optical filter is used for filtering other components except the central wavelength of the emergent laser;

the isolator only allows the laser to pass through in a single direction and is used for preventing the backward returning light from damaging the pulse seed source and an optical path system thereof;

the first half-wave plate is used for adjusting the polarization angle of the linear polarization seed light so that the linear polarization seed light can completely penetrate through the polarization beam splitter;

the first lens is used for adjusting the radius of a light spot of seed laser entering a gain medium to be 300 mu m;

the 45-degree Faraday rotator is used for rotating the polarization direction of the laser by 45 degrees;

the second half-wave plate is used for adjusting the polarization angle of the laser before the laser enters the gain medium;

the first reflector is used for reflecting the seed laser and transmitting the pump light to enter the gain medium;

the coupling lens group is used for adjusting the pump light;

the driving power supply is used for adjusting the working current of the laser diode.

Further, the driving power supply controls the laser diode to emit pumping pulses with the same repetition frequency as the seed laser.

Further, when the gain medium is amplified, the ratio of the size of the seed light spot to the size of the pumping light spot is larger than 1.

The method and the system have the beneficial effects that: the invention adopts the end-pumped rod-shaped laser medium amplification mode to ensure that the roundness of the output light spot is high, the beam shaping is not needed, the structure is simple and compact by adopting the two-pass amplification mode, and the laser diode pulse pumping mode is suitable for long-term stable use.

Drawings

FIG. 1 is a schematic diagram of a high efficiency rod laser amplifier according to an embodiment of the present invention;

fig. 2 is a diagram illustrating a beam quality measurement diagram and a near-far field spot topography of an amplified laser output from a high-efficiency rod laser amplifier according to an embodiment of the present invention.

Reference numerals: 1. a pulsed seed source; 2. an optical filter; 3. an isolator; 4. a first half wave plate; 5. a first lens; 6. a polarizing beam splitter; 7. a 45 ° faraday rotator; 8. a second half-wave plate; 9. a first reflector; 10. a gain medium; 11. a second reflector; 12. a second convex lens; 13. a third reflector; 14. a coupling lens group; 15. a laser diode; 16 a drive power supply;

Detailed Description

The invention is described in further detail below with reference to the figures and the specific embodiments. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

As shown in fig. 1, the invention provides a high-efficiency rod-shaped laser amplifier, which includes a pulse seed source 1, an isolation adjustment unit, a two-way amplifier main body and a pump coupling control unit, wherein laser emitted from the pulse seed source 1 sequentially passes through the isolation adjustment unit and the two-way amplifier main body, the pump coupling control unit provides pump energy, the isolation adjustment unit sequentially includes an isolator 3, a first half-wave plate 4 and a first lens 5 along the advancing direction of the emitted laser, the two-way amplifier main body sequentially includes a polarization beam splitter 6, a 45 ° faraday rotator 7, a second half-wave plate 8, a first reflector 9, a gain medium 10, a second lens and a third reflector 13 along the advancing direction of the emitted laser, and the pump coupling control unit includes a laser diode 15, a coupling lens group 14 and a driving power supply 16.

Further as a preferred embodiment of the present invention, the isolation adjusting unit further includes an optical filter 2, and the optical filter 2 is disposed between the isolator 3 and the pulse seed source 1.

Further as a preferred embodiment of the present invention, the second lens is a convex lens, and a distance between the second lens and the third reflector 13 and a distance between the second lens and the exit end face of the gain medium are both equal to a focal length of the second lens.

Further as a preferred embodiment of the present invention, the double-pass amplifier body further comprises a second mirror 11, and the second mirror 11 is disposed between the gain medium 10 and the second convex lens 12.

Further as a preferred embodiment of the present invention, the first mirror 9 and the second mirror 11 are both mirrors having high reflectivity for the seed laser wavelength and high transmittance for the pump light wavelength.

Specifically, in this embodiment, the pulse seed source is a commercial passively Q-switched microchip laser, the central wavelength of the output laser is 1064nm, the pulse width is about 950ps, the repetition frequency is 1kHz, and the single pulse energy is 39 μ J.

Optionally, the filter 2 is used to filter out other components outside the central wavelength of the emitted laser, such as 808nm pump light.

The isolator 3 only allows the laser to pass through in a single direction, and prevents the backward returning light from damaging the pulse seed source 1 and an optical path system thereof.

The first half-wave plate 4 is used to adjust the polarization angle of the linearly polarized seed light to make it completely transmit through the polarization beam splitter 6.

The first lens 5 is a convex lens with a focal length of 100mm and is used for adjusting the radius of a light spot of the seed laser to be 300 mu m when the seed laser enters the gain medium.

The 45 ° faraday rotator 7 can rotate the laser polarization direction by 45 °. When the laser light after the second-pass amplification passes through again, the polarization direction rotates 45 degrees again due to the magneto-optical effect, and then the laser light is reflected by the polarization beam splitter 6 to be output.

The second half-wave plate 8 is used for adjusting the polarization angle of the laser before the laser enters the gain medium so as to obtain the optimal amplification effect.

The first reflector 9 and the second reflector 11 have high reflectivity for 1064nm seed laser and high transmittance for 878nm pump light. The first mirror 9 reflects the seed laser light and transmits the pump light into the gain medium 10. The entrance end face of the gain medium 10 is defined as the face close to the first mirror 9, and the exit end face is defined as the face close to the second mirror 11.

The gain medium 10 is an a-axis cut Nd: YVO4 bonded crystal with a doping concentration of 0.3 at.% and a size of 3 × 3 × (2+16+2) mm 3. Except the laser emitting end face, the periphery of the crystal is surrounded by a red copper metal block for heat dissipation, and a cooling liquid channel is arranged in the metal block and assisted by deionized water circulating water cooling for heat dissipation.

The second lens 12 and the third mirror 13 constitute an optical 4f system. The second lens 12 is a convex lens with a focal length of 100 mm. The third mirror 13 has a high reflectivity for 1064nm laser light. The optical 4f system means that the distances from the second lens 12 to the third reflector 13 and to the emergent end face of the gain medium 10 are equal to the focal length of the second lens 12.

The laser diode 15 outputs pumping light with the wavelength of 878nm, and the diameter of the fiber core of the coupling optical fiber is 200 mu m. The coupling lens group comprises two convex mirrors, and the pump light is focused to the radius of 200 mu m through adjustment, and the light waist falls in the bonded crystal which is about 3mm away from the incident end face. At the moment, the ratio of the seed light spot to the pumping light spot is about 1.5, and the method has a better amplification effect. The driving power supply adjusts the working current of the laser diode 15, so that the laser diode 15 outputs pulse laser with repetition frequency of 1kHz and adjustable pulse width and peak power, and the pulse time appearance is approximate to rectangular wave. The pump pulse and the seed laser pulse can be synchronized by adjusting the time delay, and the maximum amplification effect is obtained.

The principle of the high efficiency rod laser amplifier of the present invention is explained in detail below. As mentioned above, the pulse laser emitted from the pulse seed source 1 passes through the isolation adjustment unit sequentially composed of the optical filter 2, the isolator 3, the first half-wave plate 4 and the first lens 5, and then enters the main body of the double-pass amplification structure. In order to obtain a better amplification effect and improve the conversion efficiency of the pump light, in this embodiment, the ratio of the seed light spot to the pump light spot (hereinafter referred to as the light spot ratio) is set to 1.5. The spot ratio is more than 1, which means that the pumping spot is small, the energy is relatively concentrated, and the part with higher intensity in the seed spot is amplified, so that the overall gain is higher. However, if in the case of high intensity continuous pumping, the smaller pump spot creates a larger temperature gradient, resulting in severe thermal effects, greatly degrading beam quality. Under the condition, the pulse pumping mode is used instead, so that the heat accumulation can be effectively reduced, and the heat effect is reduced. On the other hand, because the repetition frequency is low (1kHz), and the Nd: YVO4 is about 100 mus, compared with continuous pumping, the pulse pumping method can effectively reduce the consumption of the upper level inversion population number in the non-amplification process and improve the pumping energy conversion efficiency. After the first-pass amplification, the pumping energy still remains, and the pumping energy can be further extracted through the second-pass amplification. By means of the optical 4f system, when the laser returns to the emergent end face of the gain medium 10, the appearance of the light spot is consistent with that of the light spot emergent from the emergent end face, so that the excellent light spot ratio is still kept in the second-pass amplification process, a good amplification effect is obtained, and the pumping conversion efficiency is improved.

In this embodiment, under the conditions of a pumping peak power of 56W and a pumping pulse width of 170 μ s, after the seed laser with a single pulse energy of 39 μ J is amplified in two passes, the pulse energy can be increased to 2.7mJ, the peak power reaches 3.55MW, and the corresponding pumping conversion efficiency is 28.4%. Please refer to fig. 2. Fig. 2 is a beam quality measurement diagram of the amplified laser at this time. As can be seen from fig. 2, the amplified laser still maintains good beam quality (1.25 and 1.35 in the x-direction and the y-direction, respectively), and the spot sizes in the x-direction and the y-direction are close to each other, and the roundness of the spot is high. In addition, if the pump pulse width is reduced to 60 μ s, the pump conversion efficiency can exceed 30%.

The invention adopts an end-pumped rod-shaped laser medium amplification mode, the roundness of an output light spot is high, and light beam shaping is not needed; the double-pass amplification mode is adopted, the structure is simple and compact, and the device is suitable for long-term stable use; the laser diode pulse pumping mode is adopted, so that the extra consumption of pumping light is reduced, the thermal effect is reduced, and the conversion efficiency of the pumping light is improved; the seed light spot and the pumping light spot are adjustable, the ratio of the seed light spot to the pumping light spot is more than 1, a better amplification effect can be achieved, and the pumping light conversion efficiency is improved; by combining the 4f optical system, the laser can keep a better ratio of the seed light spot to the pumping light spot in the two amplification processes, and the conversion efficiency of the pumping light is improved;

a method for operating a high efficiency rod laser amplifier, comprising:

the laser emitted by the pulse seed source sequentially passes through an optical filter 2, an isolator 3, a first half-wave plate 4, a first lens 5, a polarization beam splitter 6, a 45-degree Faraday rotator 7, a second half-wave plate 8, a first reflector 9, a gain medium 10, a second reflector 11, a second convex lens 12 and a third reflector 13;

the laser diode 15 is used as a pumping source, enters the coupling lens group 14 after being output by the coupling optical fiber, and vertically enters the end face of the gain medium 10 after penetrating through the first reflector 9;

the optical filter 2 is used for filtering other components except the central wavelength of the emergent laser;

the isolator 3 only allows the laser to pass through in a single direction and is used for preventing the backward returning light from damaging the pulse seed source 1 and an optical path system thereof;

the first half-wave plate 4 is used for adjusting the polarization angle of the linearly polarized seed light so as to enable the linearly polarized seed light to completely penetrate through the polarization beam splitter 6;

the first lens 5 is used for adjusting the spot radius of the seed laser to 300 μm when the seed laser enters the gain medium 10;

the 45-degree Faraday rotator 7 is used for rotating the polarization direction of the laser by 45 degrees;

the second half-wave plate 8 is used for adjusting the polarization angle of the laser before the laser enters the gain medium 10;

the first reflector 9 is used for reflecting the seed laser and transmitting the pump light to enter the gain medium 10;

the coupling lens group 14 is used for adjusting pump light;

the driving power supply 16 is used for adjusting the working current of the laser diode 15.

Further as a preferred embodiment of the method, the driving power supply 16 controls the laser diode 15 to emit the pump pulse with the same repetition frequency as the seed laser.

Further as a preferred embodiment of the method, when the gain medium 10 is amplified, the ratio of the sizes of the seed light spot and the pump light spot is greater than 1.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.