A regenerative amplifier with lens compensating for thermal lens effect of Ti:Sapphire

Abstract

The present invention belongs to the field of laser technology, and specifically relates to a regenerative amplifier with a lens that compensates for the thermal lens effect of titanium sapphire. The amplifier comprises a seed light source, a gain medium, a pump source, and a seed light reflector system. The pump light generated by the pump source is used to excite the gain medium, providing energy for amplifying the seed light generated by the seed light source. The seed light reflector system is arranged on the optical path of the seed light to amplify the seed light by causing the seed light to pass through the gain medium multiple times through reflection. The amplifier also comprises a compensation lens arranged on the optical path of the seed light to pass the seed light amplified by the gain medium through the compensation lens, thereby reducing the influence of the thermal lens effect of the gain medium on the amplified seed light. That is, the present invention only requires the arrangement of a compensation lens on the optical path of the seed light to achieve the effect of avoiding the influence of the thermal lens effect of the gain medium on the seed light. Compared with the liquid nitrogen cryogenic refrigeration of the prior art, the amplifier is very simple and convenient, and is easy to control, adjust, and maintain later.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to a regenerative amplifier with a lens compensating for a titanium sapphire thermal lens effect. Background Art

[0002] Titanium sapphire, due to its excellent thermal conductivity, high mechanical durability, and wide amplification bandwidth, is used in chirped pulse amplification (CPA) technology because its properties enable the generation of ultra-high-power laser pulses. For example, pulsed lasers with powers exceeding 10 PW have a wide range of applications in laser-material interactions, particle acceleration, and extreme scientific research and medical applications. However, when titanium sapphire, acting as a gain medium, absorbs pump light, some of the energy is stored within the gain medium, causing it to heat up. In thermal equilibrium, the temperature gradient within the gain medium transforms it into a lens-like medium, a phenomenon known as thermal lensing. This thermal lensing effect not only distorts the wavefront of the amplified laser seed beam but also causes it to focus. This leads to a spatial mode mismatch between the laser seed source and the pump light, reducing the output energy efficiency and affecting the shape of the output spot.

[0003] The main difficulty to be overcome in designing a high average power Ti:Sapphire amplifier is the thermal lens. In fact, ignoring the effects of stress and thermal expansion, the focal length of the thermal lens induced in the Ti:Sapphire crystal can be expressed as: Where r is the pump beam radius, P P is the pump power, n is the refractive index of the crystal, η is wavelength-dependent and is the ratio of pump power dissipated as heat, and K is the thermal conductivity. Therefore, the thermal focal length of Ti:sapphire is related to the pump power, the crystal refractive index, and the wavelength-dependent thermal conductivity.

[0004] Temperature gradients within the Ti:sapphire gain medium cause changes in the refractive index, while thermal expansion and photoelastic effects of the medium cause bending and deformation of the Ti:sapphire surface. These three factors are specific manifestations of the thermal lensing effect. The thermal lensing effect is related to the pump repetition rate. If the pump repetition rate is between 10Hz and 100Hz, the Ti:sapphire thermal lensing effect is minimal. However, if the pump repetition rate exceeds 1000Hz, the Ti:sapphire thermal lensing effect becomes severe, affecting the output spot shape and output energy. Currently, one approach to addressing the Ti:sapphire thermal lensing effect is to use cryogenic cooling technology, using liquid nitrogen to lower the Ti:sapphire surface temperature to 77K. This liquid nitrogen removes the heat generated by the pump source from the Ti:sapphire, minimizing the thermal lensing effect. However, this method requires the amplification system to be submerged in liquid nitrogen, making the setup complex and difficult to implement, hindering subsequent debugging and maintenance. Summary of the Invention

[0005] The purpose of the present invention is to provide a regenerative amplifier with a lens that compensates for the thermal lens effect of titanium sapphire, so as to solve the problem that the existing technology uses liquid nitrogen to solve the thermal lens effect of titanium sapphire, which has a complex device and is not conducive to subsequent debugging and maintenance.

[0006] In order to solve the above technical problems, the present invention provides a regenerative amplifier with a lens that compensates for the thermal lens effect of titanium sapphire, comprising a seed light source, a gain medium, a pump source, and a seed light reflector system composed of a plurality of reflectors; the pump light generated by the pump source is used to excite the gain medium to provide energy for amplifying the seed light generated by the seed light source, the seed light reflector system is arranged on the optical path of the seed light, so as to reflect the seed light so that the seed light passes through the gain medium multiple times and the seed light is amplified multiple times, and also includes a compensation lens, which is arranged on the optical path of the seed light to pass the seed light amplified by the gain medium through the compensation lens, so as to reduce the influence of the thermal lens effect of the gain medium on the amplified seed light.

[0007] Its beneficial effects are as follows: the present invention uses a compensating lens to weaken the thermal lens effect of the gain medium after the seed light passes through the gain medium, thereby avoiding the influence of the output light spot and energy caused by the thermal lens effect of the gain medium. Therefore, the present invention does not avoid the thermal lens effect of the gain medium by placing the gain medium within a set temperature range as in the prior art, but offsets the thermal lens effect of the gain medium caused by the high temperature by adding a compensating lens. Moreover, the regenerative amplifier of the present invention only needs to set a compensating lens on the optical path of the seed light to achieve the effect of avoiding the influence of the thermal lens of the gain medium on the seed light. Compared with the liquid nitrogen low-temperature refrigeration in the prior art, it is very simple and convenient, and easy to control, adjust and maintain in the later stage.

[0008] Furthermore, the compensation lens includes at least one concave lens.

[0009] Furthermore, the placement position of the concave lens and the parameters of the concave lens are determined by performing software simulation on the amplifying cavity of the regenerative amplifier.

[0010] In order to enable the compensation lens to better offset the influence of the thermal lens effect caused by the high temperature of the gain medium, the present invention can determine the parameters and position of the compensation lens by pre-using software simulation, thereby enabling the compensation lens to better realize thermal lens effect compensation.

[0011] Furthermore, it also includes a pump light reflector system for reflecting pump light, and the pump light reflector system includes two reflectors respectively arranged on both sides of the gain medium, so that the pump light is first reflected by one of the reflectors and then injected into the first side of the gain medium, so that the residual energy of the pump light after passing through the gain medium is emitted from the second side of the gain medium to the other reflector, and then injected into the second side of the gain medium after being reflected by the other reflector.

[0012] Furthermore, the gain medium is a titanium sapphire crystal, and the reflectors on both sides of the titanium sapphire crystal are located on a straight line passing through the titanium sapphire crystal.

[0013] Furthermore, a convex lens is respectively arranged between the reflectors on both sides of the gain medium and the gain medium.

[0014] The present invention allows the pump light generated by the pump source to be reflected by a reflector and then enter the gain medium twice, so that the pump light generated by the pump source can be fully absorbed by the gain medium to provide energy for amplifying the seed light. In addition, before entering the gain medium twice, the pump light is focused by a convex lens and then enters the gain medium, so that the energy of the pump light is concentrated and the gain medium better absorbs the energy of the pump light to provide energy for amplifying the seed light.

[0015] Furthermore, the seed light reflector system includes a deflecting mirror group and a dichroic mirror group, the dichroic mirror group includes two dichroic mirrors respectively arranged between convex lenses on both sides of the gain medium and the gain medium; the dichroic mirrors are used to transmit pump light, and one of the dichroic mirrors is used to reflect the seed light passing through the gain medium to the deflecting mirror group, the deflecting mirror group is used to reflect the received seed light to the other dichroic mirror, and the other dichroic mirror is used to reflect the received seed light toward the gain medium.

[0016] The present invention can achieve the amplification process of the seed light by allowing the seed light to pass through the gain medium multiple times in a circular optical path by setting a dichroic mirror group and a reversing mirror group. Compared with the situation where the optical path of the seed light does not overlap when the reflector group is set, in this case, if the reflector group is determined, the number of times the seed light passes through the gain medium is determined. Therefore, the setting of the circular optical path of the present invention makes the number of times the seed light passes through the gain medium adjustable, so that the output energy of the seed light can be met under different circumstances. In addition, the reflector system setting based on the circular optical path of the present invention reduces the number of devices used compared to the reflector system setting based on the non-overlapping optical path, and thus the device structure of the present invention is simpler.

[0017] Furthermore, a Pockels cell is provided on the optical path of the seed light in the deflection mirror assembly to screen the set seed light from the seed light when the seed light enters the deflection mirror assembly for the first time.

[0018] Furthermore, by setting a time delay for opening the high-voltage switch of the Pockels cell, the set seed light can be screened from the seed light when the seed light first enters the reversing mirror group.

[0019] Furthermore, it also includes a polarization beam splitter prism, which is used to guide the seed light that has been amplified multiple times out of the cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of the laser amplification system of the present invention;

[0021] Figure 2 It is a schematic diagram of the structural principle of the regenerative amplifier of the present invention.

[0022] Among them, 1. First 532nm reflector; 2. First 532nm lens; 3. Second 532nm lens; 4. Second 532nm reflector; 5. Ti:Sapphire gain medium; 6. First 800nm ​​reflector and 532nm transmit dichroic mirror; 7. First 800nm ​​reflector; 8. Compensating lens; 9. Pockels cell; 10. Second 800nm ​​reflector; 11. Second 800nm ​​reflector and 532nm transmit dichroic mirror; DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Embodiment of a regenerative amplifier with lens compensating for thermal lens effect of Ti:Sapphire:

[0025] In order to avoid the problem that the thermal lens effect caused by the temperature increase of the gain medium affects the amplification of the seed light, the regenerative amplifier of this embodiment provides a compensation lens to offset the influence of the thermal lens effect on the amplification of the seed light.

[0026] The regenerative amplifier in this embodiment is used in Figure 1 In the laser amplification system shown, the seed light output by a femtosecond laser oscillator enters a stretcher for time-domain stretching, extending the seed light pulse width from femtoseconds to picoseconds. A pump source provides energy to the gain medium, amplifying the seed light output by the oscillator. A lens (compensation lens) is placed in the regenerative cavity amplifier to compensate for the thermal lensing effect of the pump source on the titanium sapphire. The energy of a single pulse of seed light is increased from nanojoules to millijoules, amplifying it by six orders of magnitude. After being amplified by the regenerative amplifier, the seed light enters a compressor for pulse width compression. The picosecond seed light is compressed again to the femtosecond level.

[0027] The structural principle diagram of the regenerative amplifier in this embodiment is as follows Figure 2 As shown, it includes a seed light reflector group (i.e., a dichroic mirror group consisting of a first 800nm ​​reflecting 532nm transmitting dichroic mirror 6 and a second 800nm ​​reflecting 532nm transmitting dichroic mirror 11, a first 800nm ​​reflecting mirror 7 and a second 800nm ​​reflecting mirror 10 consisting of a reversing mirror group), a pump light reflector group (i.e., a first 532nm reflecting mirror 1 and a second 532nm reflecting mirror 4), a compensation lens 8, a titanium sapphire gain medium 5, a seed light source and a pump source (the seed light source and the pump source are not shown Figure 2In the figure, the pump light generated by the specific pump source is first reflected by the first 532nm reflector 1, then focused by the first 532nm lens 2 and transmitted by the first 800nm ​​reflecting 532nm transmitting dichroic mirror, and then incident on the titanium sapphire gain medium 5 at the Brewster angle. The remaining energy after passing through the titanium sapphire passes through the 532nm reflector 4, and is again focused by the second 532nm lens 3 and the second 800nm ​​reflecting 532nm transmitting dichroic mirror 11, and then incident on the titanium sapphire, providing energy for the amplification of the seed light. The seed light in the P polarization state is incident on the titanium sapphire at the Brewster angle, and is reflected by the titanium sapphire and hits the first 800nm ​​reflecting 532nm transmitting dichroic mirror 6. The first 800nm ​​reflecting 532nm transmitting dichroic mirror 6 reflects the seed light onto the first 800nm ​​reflecting mirror 7. At this time, the high-voltage switch of the Pockels cell 9 is turned on, and a pulse is selected for amplification. The selected P polarization state seed light hits the second 800nm ​​reflecting mirror 10. The second 800nm ​​reflecting mirror 10 then reflects the seed light onto the second 800nm ​​reflecting 532nm transmitting dichroic mirror 11. The second 800nm ​​reflecting 532nm transmitting dichroic mirror 11 then hits the titanium sapphire gain medium 5 at the Brewster angle, absorbs the energy of the titanium sapphire, and starts to amplify it one by one in the cavity. Finally, by opening another channel switch of the Pockels cell 9, the amplified light is selected, and then the amplified pulse is led out of the cavity. In this embodiment, the amplified pulse is led out of the cavity after passing through a PBS (polarization beam splitter prism). Because the titanium sapphire gain medium absorbs the pump source energy, part of it is converted into heat, making the titanium sapphire a thermal lens. Due to the thermal lens effect, the selected seed light will cause the light field pattern to change during the amplification process, the light spot to deform, and the output energy to decrease. At this time, through software simulation of the cavity mode, a concave lens with a focal length of 1m is selected, which should be placed in the larger position of the cavity mode shown in the figure (i.e., the position of the compensation lens 8). The compensation lens 8 in the cavity can compensate for the thermal lens effect of the titanium sapphire. Each time it passes through the titanium sapphire, the seed light is amplified, and then it is compensated by the compensation lens before entering the titanium sapphire for amplification again. Therefore, the thermal lens effect can be offset by the compensation lens. In this way, each time it passes through the titanium sapphire for amplification, the thermal lens effect will be offset once through the lens. Finally, by adjusting the pump source energy, the time interval between the pump source and the seed light, and the time the seed light is amplified in the cavity, the output energy is maximized. Finally, the light field pattern returns to the fundamental mode, the light spot is no longer deformed, and the output energy is increased.

[0028] The Pockels cell 9 in this embodiment delays the opening of the high-voltage switch of the Pockels cell so that the high-voltage switch of the Pockels cell 9 is turned on when the seed light is first reflected by the first 800nm ​​reflector 7. After the seed light has been amplified multiple times, the amplified light can be selected by turning on another channel switch of the Pockels cell. In this embodiment, the pump light generated by the pump source is reflected by the reflector and then enters the gain medium twice, so that the pump light generated by the pump source can be fully absorbed by the gain medium to provide energy for the amplification of the seed light. In addition, the pump light is focused by a convex lens before entering the gain medium twice, so that the energy of the pump light is concentrated and the gain medium can better absorb the energy of the pump light to provide energy for the amplification of the seed light. In this embodiment, by setting a dichroic mirror group and a reversing mirror group, the seed light can pass through the gain medium multiple times in a circular optical path to realize the seed light amplification process. Compared with the situation where the optical path of the seed light does not overlap when the reflector group is set, in this case, if the reflector group is determined, the number of times the seed light passes through the gain medium is determined. Therefore, the setting of the circular optical path in this embodiment makes the number of times the seed light passes through the gain medium adjustable, so that the output energy of the seed light can be met under different circumstances. In addition, the reflector system setting based on the circular optical path in this embodiment reduces the number of devices used compared to the reflector system setting based on the non-overlapping optical path, and thus the device structure of the present invention is simpler.

[0029] The regenerative amplifier of this embodiment avoids the influence of the output light spot and energy caused by the thermal lens effect of the gain medium by using a compensation lens to weaken the thermal lens effect of the gain medium after the seed light passes through the gain medium. Therefore, the regenerative amplifier of this embodiment does not avoid the thermal lens effect of the gain medium by placing the gain medium within a set temperature range as in the prior art, but offsets the thermal lens effect of the gain medium caused by the high temperature by adding a compensation lens. Moreover, the regenerative amplifier of this embodiment only needs to set a compensation lens on the optical path of the seed light to achieve the effect of avoiding the influence of the thermal lens of the gain medium on the seed light. Compared with the liquid nitrogen low-temperature refrigeration of the prior art, it is very simple and convenient, easy to control and adjust, and easy to maintain in the later stage. This solution saves space and greatly reduces costs.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the description and drawings of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A regenerative amplifier with a lens that compensates for the thermal lens effect of titanium sapphire, comprising a seed light source, a gain medium, a pump source, and a seed light reflector system consisting of a plurality of reflectors; the pump light generated by the pump source is used to excite the gain medium to provide energy for amplifying the seed light generated by the seed light source; the seed light reflector system is arranged on the optical path of the seed light to reflect the seed light so that the seed light passes through the gain medium multiple times, thereby being amplified multiple times, characterized in that: The invention also includes a compensation lens, which is arranged on the optical path of the seed light to pass the seed light amplified by the gain medium through the compensation lens, so as to reduce the influence of the thermal lens effect of the gain medium on the amplified seed light; and a pump light reflector system for reflecting the pump light, wherein the pump light reflector system includes two reflectors respectively arranged on both sides of the gain medium, so that the pump light is first reflected by one of the reflectors and then injected from the first side of the gain medium, so that the residual energy of the pump light after passing through the gain medium is emitted from the second side of the gain medium to the other reflector, and is reflected by the other reflector and injected from the second side of the gain medium; the seed light reflector system includes a reversing mirror group and a two-color mirror group. A mirror assembly, wherein the dichroic mirror assembly includes two dichroic mirrors respectively arranged between reflectors on both sides of a gain medium and the gain medium; the dichroic mirrors are used to transmit pump light, and one of the dichroic mirrors is used to reflect seed light passing through the gain medium to a reversing mirror assembly, the reversing mirror assembly is used to reflect the received seed light to the other dichroic mirror, and the other dichroic mirror is used to reflect the received seed light toward the gain medium; a Pockels cell is further provided on the optical path of the seed light in the reversing mirror assembly to screen and set the seed light from the seed light when the seed light first enters the reversing mirror assembly; and by setting the time for delaying the opening of the high-voltage switch of the Pockels cell, the seed light is screened and set from the seed light when the seed light first enters the reversing mirror assembly.

2. The regenerative amplifier for compensating the thermal lens effect of titanium sapphire according to claim 1, characterized in that: The compensation lens includes at least one concave lens.

3. The regenerative amplifier for compensating the thermal lens effect of titanium sapphire according to claim 2, characterized in that: The placement position of the concave lens and the parameters of the concave lens are determined by performing software simulation on the amplifying cavity of the regenerative amplifier.

4. The regenerative amplifier for compensating the thermal lens effect of Ti:Sapphire according to claim 1, characterized in that: The gain medium is a titanium sapphire crystal, and the reflectors on both sides of the titanium sapphire crystal are located on a straight line passing through the titanium sapphire crystal.

5. The regenerative amplifier for compensating the thermal lens effect of Ti:Sapphire according to claim 4, characterized in that: A convex lens is respectively arranged between the reflector and the dichroic mirror on both sides of the gain medium.

6. The regenerative amplifier for compensating the thermal lens effect of Ti:Sapphire according to claim 1, characterized in that: The invention also comprises a polarization beam splitter prism, which is used to guide the seed light after multiple amplification out of the cavity.

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