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随着技术的发展和相关应用的推广，超短脉冲激光及其与物质相互作用的研究成为目前比较热门的领域之一[1-2]，为了得到更高能量以及更高质量的激光脉冲输出，产生高功率放大超快脉冲的技术也在迅速发展，在脉冲能量和脉冲峰值功率上不断突破[3]。Phung V.L.J等开发了一种由钛宝石振荡器、拉伸光栅、钛宝石再生放大器等组成的钛宝石激光放大系统，其峰值功率大于1 TW，脉冲持续时间为34 fs，中心波长为800 nm，重复频率为10 Hz[4]。 Patokoski K 等在百纳秒单频脉冲放大系统的功率放大级，使用输出端直径为50 μm的掺镱锥形光纤有效抑制布里渊散射，脉冲能量为 0.52 mJ的1053 nm百纳秒单频脉冲激光的峰值功率达到了破纪录的 4 kW[5]。Sonnenschein V等将CW Ti:sapphire振荡器和脉冲放大器组合在单个光学腔中，蓝色波长半导体二极管的二向色光束组合和Nd：YAG激光器的绿色波长同时激发Ti：蓝宝石晶体，可实现激光脉冲持续时间为73 ns，峰值脉冲强度为0.2 kW[6]。杨保来等提出并验证了新型981 nm稳波长泵浦方案，采用白噪声相位调制展宽单频激光作为窄谱种子，通过单端后向泵浦结构，将单模窄谱光纤放大器功率提至4 kW以上[7]。刘彦祺等开展并验证了钛宝石晶体拼接技术的可行性，搭建了钛宝石晶体拼接的啁啾脉冲激光放大器，最终获得了5 J脉冲放大输出，脉冲峰值功率可达100 TW[8]。
使用钛宝石固体激光器产生的飞秒激光脉冲作为种子光源，经三倍频后，再用准分子激光放大器进行脉冲放大，可以获得高功率紫外超短脉冲激光[9]。Mossiv.k等利用ArF准分子激光放大器将单脉冲能量为12 μJ、脉宽300 fs的193 nm深紫外超短脉冲种子光放大到脉宽710 fs、能量8 mJ[10]。Yasuo Nabekawa等利用钛宝石飞秒激光器输出248 nm脉冲激光为种子光，利用多程放大光路将功率提高到50 W，脉宽为480 fs[11]。西北核技术研究所的刘学庆团队研制的XeCl准分子激光系统将单脉冲能量提高到100 J，脉宽为10 ns[12]。当种子源经信号控制器发出工作信号，准分子激光放大器相应地接收到信号控制器发出的触发信号。在实际应用中，由于脉冲激光的自发辐射噪声、准分子激光器腔体的震动和移动以及控制电路的触发信号的不稳定等多种因素影响，从而引起种子光在信号控制器作用下的脉冲重复频率的不稳定性，发生时间抖动现象[13-14]。在准分子激光放大器达到热平衡过程中出光信号延迟时间发生漂移，出现温漂现象。
为了解决飞秒种子光与准分子激光放大器之间的时间同步问题，文中研究了以氢闸流管作为高压开关的准分子激光放大器的运行重复率、工作电压和气体状态三种因素对出光延迟时间和出光时间温漂现象的影响。
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因准分子激光放大器一般要求种子光达到激光放大器的时刻与激光放大器放电时候精确同步[15]，因此对准分子激光放大器进行了低抖动工作模式设计。如图1所示，低抖动准分子激光放大器系统由三个模块组成，固体种子源接收信号控制器输出的固体种子光工作信号发出种子光，外部的信号控制器输出出光信号和充电信号控制准分子激光放大器进入工作模式，种子光和准分子放电触发的信号之间会发生出光延时和时间抖动现象。
图 1 固体种子源与准分子激光放大器模块间基本连接图
Figure 1. Basic connection diagram between solid seed source and excimer laser amplifier module self-injection
准分子激光放大器内部工作原理如图2所示，外部的充电信号和出光信号两个信号经过转换电路分别转换成闸流管触发光信号和高压电源的充电光信号。闸流管触发光信号用于触发闸流管导通。通过外部触摸屏给内部控制电路设置一个高压基准信号，充电光信号和高压基准信号决定了高压电源的输出电压。
准分子激光放大器各个控制信号时序图如图3所示。
图 2 准分子激光放大器内部工作原理图
Figure 2. Internal working principle diagram of excimer laser amplifier
图 3 控制信号时序图
Figure 3. Control signal sequence diagram
在外部设计了一块可以产生外部充电信号和出光信号的电路板，可以获得上升沿约5 ns范围内的出光信号，如图4所示。
图 4 出光信号上升沿
Figure 4. Rising edge of light output signal
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外部出光信号与闸流管触发信号的抖动时间在控制在4 ns的范围内，如图5所示，CH1波形为控制准分子激光放大器电极放电的外部出光信号，CH2为触发闸流管导通的闸流管触发信号。外部出光信号和闸流管触发信号出光延迟时间一般固定不变，大约为250 ns。
图 5 （a）外部出光信号和闸流管触发信号；（b） 30 min后闸流管触发信号时间抖动的范围在4 ns
Figure 5. (a) External light output signal and thyristor trigger signal; (b) After 30 min, the time jitter range of thyristor trigger signal is 4 ns
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高压电源在电源充电信号和高压平顶信号的控制下产生高压，给高压储能电容充电。电源充电波形和高压信号波形见图3。在外部出光信号的作用下，氢闸流管导通，高压储能电容的能量转移到放电电容上，放电电容通过电极放电[16]。准分子工作气体在放电泵浦和谐振腔的作用下产生激光。
实验使用的是PLD20准分子激光器，激光波长为248 nm，重新洗气配气后激光脉冲平均能量为184.3 mJ。在激光激光放大器热平衡过程中，延迟时间会产生延时漂移，即温漂。温漂是单向的，沿着延迟时间变大的方向漂移，如图6所示。
在触摸屏上设置准分子激光放大器重复频率分别为5、10、15 Hz，运行电压分别为24、25、26、27、28、29 kV，通过光电探测器实时探测外部出光信号与准分子激光放大器的光脉冲信号的抖动及延迟时间，比较在相同重复频率下不同的运行电压的数据，由多次实验数据测得，当准分子激光放大器重复频率为5 Hz时，光脉冲达到稳定延时需要运行的脉冲数为6k pusles；当准分子激光放大器重复频率为10 Hz时，光脉冲达到稳定延时需要运行的脉冲数为12k pusles；当准分子激光放大器重复频率为15 Hz时，光脉冲达到稳定延时需要运行的脉冲数为18k pusles。图7为在24~29 kV运行电压下测得的在不同频率下的稳定延时时间的数据对比图。
图 6 外部出光信号控制的延时、延时漂移和抖动
Figure 6. Delay, delay drift and vibration of external light output signal control
图 7 相同重复频率下不同的运行电压的稳定延时时间
Figure 7. Stable delay time of different operating voltages under the same repetition frequency
由图7可知，在激光重复频率为5 Hz时，运行电压越高，光脉冲的稳定延迟时间越小；在激光重复频率为10 Hz时，不同的运行电压的光脉冲的稳定延迟时间相差较小，而当激光重复频率为15 Hz时，运行电压越高，光脉冲的稳定延迟时间越大。相同运行电压的稳定延迟时间随着重复频率的增大呈现上升的趋势，运行电压越高，曲线上升的幅度越大。当准分子激光放大器达到热平衡后，出光延时稳定在一个固定值，20k pulse激光脉冲出光抖动时间控制在5 ns内。
将准分子激光放大器放置一星期后，由于氟气与含碳材料反应生成激光淬灭物质CF4[17]，氟气浓度的下降将导致准分子激光更容易进行放电激励过程，则使得准分子激光放大器达到热平衡的出光延迟时间缩短。而氟气的消耗和激光淬灭物质的产生将使得激光脉冲平均能量减小，从184.3 mJ下降至146 mJ。在触摸屏上设置激光运行电压为25、26 kV，重复频率为5、10 Hz，分别测得当气体恶化后准分子激光放大器在不同运行电压不同重复频率下的数据：在25 kV运行电压下，重复频率为5 Hz时的稳定延迟时间由一周前的811.6 ns降为798.0 ns；重复频率为10 Hz时的稳定延迟时间由一周前的829.6 ns降为808.4 ns。在26 kV运行电压下，重复频率为5 Hz时的稳定延迟时间由一周前的809.6 ns降为795.2 ns；重复频率为10 Hz时的稳定延迟时间由一周前的820.8 ns降为808.0 ns。可以发现，在相同的运行电压和重复频率下光脉冲的稳定延迟时间变小。图8为准分子激光放大器达到热平衡时采集20k pusles脉冲数的出光延时的抖动时间，稳定在5 ns之内。
图 8 (a) 25 kV下重复频率为5 Hz的光脉冲抖动时间；(b) 26 kV下重复频率为10 Hz的光脉冲抖动时间；(c) 气体恶化后25 kV下重复频率为5 Hz的光脉冲抖动时间；(d) 气体恶化后26 kV下重复频率为10 Hz的光脉冲抖动时间
Figure 8. (a) Vibration time of optical pulse with repetition frequency of 5 Hz at 25 kV; (b) Vibration time of optical pulse with repetition frequency of 10 Hz at 26 kV; (c) Vibration time of optical pulse with repetition rate of 5 Hz at 25 kV after gas deterioration; (d) Vibration time of optical pulse with repetition rate of 10 Hz at 26 kV after gas deterioration
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采用以氢闸流管作为高压开关的准分子激光放电回路设计，可以达到种子光传输到准分子激光放大器的时刻与准分子激光放大器放电时刻的时间抖动为5 ns。从外部出光信号到激光放大器输出光脉冲有一定的延迟时间，实验测得在实现低抖动出光前，准分子激光放大器在热平衡稳定过程中会产生温漂现象，漂移时间主要受激光运行重复率影响，延迟时间受多个因素影响：
（1）外部控制信号转换电路和闸流管触发电路，出光延时时间一般固定不变；
（2）激光运行重复率；
（3）准分子激光放大器运行电压；
（4）准分子激光放大器工作气体状态。
由多次实验可得：5 Hz的漂移时间为6k pusles个脉冲数；10 Hz的漂移时间为12k pusles个脉冲数；15 Hz的漂移时间为18k pusles个脉冲数。在相同的运行电压下，光脉冲的稳定延迟时间随着重复频率的提高而增大，运行电压越高，光脉冲的增大幅度越大；准分子激光气体恶化后，在相同的运行电压和重复频率下光脉冲稳定延迟时间变小。
随着技术的发展和相关应用的推广，超短脉冲激光及其与物质相互作用的研究成为超快科学研究的重要领域之一，获取更高能量以及更高质量的激光脉冲输出是当前激光研究的热点。文中对准分子激光放大器的同步特性进行了研究，分析了不同因素对准分子激光放大器延迟时间的影响，成功将准分子激光放大器的抖动时间严格控制在了5 ns之内，为有效实现种子光与准分子激光放大器的同步运行提供了参考。在文中分析了准分子激光放大器运行重复率、运行电压以及工作气体状态对光脉冲稳定延迟时间的影响，实际实验过程有多种因素影响抖动时间及稳定延迟时间，如BNC接头的长度等。
Study on light source of low jitter excimer laser amplifier
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摘要: 为了获得低抖动的准分子激光放大器光源，设计了一种以氢闸流管作为高压开关的低抖动准分子激光放大器系统。利用抖动小于4 ns的闸流管触发电路来触发导通氢闸流管，从外部触发信号到准分子光信号之间有一定的延时时间。研究了以氢闸流管作为高压开关的准分子激光放电回路，外部控制信号发生电路产生外部充电信号和出光信号，转换电路将外部充电信号和出光信号转换成固定脉宽的光信号，在实现低抖动出光前，准分子激光放大器系统热平衡过程中会有一定的出光延时漂移现象。讨论了激光运行重复率、激光运行电压和气体状态在热平衡过程中对稳定延迟时间大小的影响。实验表明，在相同运行电压下，稳定延迟时间随着激光运行重复频率的提高而增大；运行电压越高，稳定延迟时间上升的幅度越大。气体恶化后，光脉冲稳定延迟时间变小。激光运行电压和重复频率越高，延时漂移时间越大。在温漂一定时间后，准分子激光放大器内部系统达到热平衡，以外部触发信号为基准，准分子光脉冲信号实现在5、10、15 Hz重复频率下的5 ns内低抖动出光。Abstract:
Significance The study of ultrashort pulse laser and its interaction with matter is one of the most popular research fields at present. In order to obtain laser pulse output with higher energy and higher quality, it is needed to make continuous breakthroughs in the research on pulse energy and peak pulse power. Compared with the solid-state laser, excimer laser with the inert gas as the gain medium has its unique advantages in the amplification of the deep ultraviolet femtosecond pulses. Using femtosecond laser pulse as the seed light source, the seed source sends the working signal through the signal controller, and the excimer laser amplifier correspondingly receives the trigger signal sent by the signal controller for pulse amplification, which can obtain high power ultraviolet ultra-short pulse laser. However, in practical application, the pulse repetition rate of seed light under the action of signal controller is unstable and time jitter occurs. Therefore, in order to improve the time synchronization between femtosecond seed light and excimer laser amplifier, the effects of three factors, namely, operation repetition rate, working voltage and gas state, on the luminescence delay time and luminescence time temperature drift of excimer laser amplifier with hydrogen thyratron as high voltage switch were studied in this paper. Progress The alignment molecular laser amplifier is designed in a low-jitter working mode with the hydrogen brake tube as a high-voltage switch (Fig.1). A thyratron trigger circuit with a jitter less than 4 ns is used to trigger the on-off hydrogen thyratron (Fig.5), which in the external design can produce an external charging signal and light signal circuit board and can get rising along the range of about 5 ns light signal (Fig.4). From the external trigger signal to the excimer light signal there is a certain delay time (Fig.5). Before realizing the low jitter light output, there will be a certain light output delay drift phenomenon in the thermal equilibrium process of the excimer laser amplifier system (Fig.6). In the laboratory, the PLD20 Excimer Laser was used to study the time synchronization characteristics of excimer amplifier, and the influence of laser operation repetition rate (Fig.7), operating voltage and gas state on the temperature drift and thermal equilibrium state (Fig.8) was discussed, which realizes the excimer light pulse signal in low jitter within 5 ns at different repetition frequencies, and provides a reference for the effective synchronous operation of seed light and excimer amplifier laser. Conclusions and Prospects A low-jitter excimer laser amplifier system with the hydrogen switch as a high voltage switch is designed. The trigger circuit with a jitter less than 4 ns is used to trigger the hydrogen gate to obtain the light signal along the range of about 5 ns. Experimental results show that the stable delay time increases with the increase of laser repetition frequency under the same operating voltage. The higher the operating voltage is, the greater the increase of the stability delay time becomes. After gas deterioration, the delay time of optical pulse stability decreases. The higher the laser operating voltage and repetition rate is, the greater the delay drift time becomes. After a certain temperature drift, the internal system of the excimer laser reaches thermal balance. Based on the external trigger signal, the excimer optical pulse signal achieves low jitter output within 5 ns at the repetition rates of 5 Hz, 10 Hz and 15 Hz. -
Key words:
- excimer laser /
- low-jitter time /
- amplifier /
- temperature drift
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图 1 固体种子源与准分子激光放大器模块间基本连接图
Figure 1. Basic connection diagram between solid seed source and excimer laser amplifier module self-injection
图 2 准分子激光放大器内部工作原理图
Figure 2. Internal working principle diagram of excimer laser amplifier
图 5 （a）外部出光信号和闸流管触发信号；（b） 30 min后闸流管触发信号时间抖动的范围在4 ns
Figure 5. (a) External light output signal and thyristor trigger signal; (b) After 30 min, the time jitter range of thyristor trigger signal is 4 ns
图 6 外部出光信号控制的延时、延时漂移和抖动
Figure 6. Delay, delay drift and vibration of external light output signal control
图 7 相同重复频率下不同的运行电压的稳定延时时间
Figure 7. Stable delay time of different operating voltages under the same repetition frequency
图 8 (a) 25 kV下重复频率为5 Hz的光脉冲抖动时间；(b) 26 kV下重复频率为10 Hz的光脉冲抖动时间；(c) 气体恶化后25 kV下重复频率为5 Hz的光脉冲抖动时间；(d) 气体恶化后26 kV下重复频率为10 Hz的光脉冲抖动时间
Figure 8. (a) Vibration time of optical pulse with repetition frequency of 5 Hz at 25 kV; (b) Vibration time of optical pulse with repetition frequency of 10 Hz at 26 kV; (c) Vibration time of optical pulse with repetition rate of 5 Hz at 25 kV after gas deterioration; (d) Vibration time of optical pulse with repetition rate of 10 Hz at 26 kV after gas deterioration
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[1] Backus S, Durfee C G, Murnane M M, et al. High power ultrafast lasers [J]. Review of Scientific Instruments, 1998, 69(3): 1207-1223. doi: doi.org/10.1063/1.1148795 [2] Liu Y Q, Leng Y X, Lu X M, et al. Splicing technology of Ti: sapphire crystals for a high-energy chirped pulse amplifier laser system [J]. High Power Laser Science and Engineering, 2014, 2(2): 1-8. doi: 10.1017/HPL.2014.11 [3] 张骥. 紫外超短脉冲激光能量储存环技术的初步研究 [D]; 北京: 中国原子能科学研究院, 2003. Zhang J. Preliminary study on ultraviolet ultrashort pulse laser energy storage ring technology [D]. Beijing: China Institute of Atomic Energy, 2003. (in Chinese) [4] Phung V, Kang K, Jeon S, et al. Development of a 1 TW/35 fs Ti:sapphire laser amplifier and generation of intense THz waves using two-color laser filamentation [J]. Multidisciplinary Digital Publishing Institute, 2021, 8(8): 316. doi: 10.3390/PHOTONICS8080316 [5] Patokoski K, Rissanen J, Noronen T, et al. Single-frequency 100 ns / 0.5 mJ laser pulses from all-fiber double clad ytterbium doped tapered fiber amplifier [J]. Optics Express, 2019, 27(22): 31532. doi: 10.1364/OE.27.031532 [6] Sonnenschein V, Tomita H. A hybrid self-seeded Ti: Sapphire laser with a pumping scheme based on spectral beam combination of continuous wave diode and pulsed DPSS lasers [J]. Applied Sciences, 2022, 12(9): 4727. doi: 10.3390/APP12094727 [7] Yang B L, Zhang H W, Wang Peng, et al. 4 kW single mode narrow linewidth fiber laser achieved in single-end pumped fiber amplifier [J]. High Power Laser and Particle Beams, 2022, 34(4): 8-9. (in Chinese) doi: 10.11884/HPLPB202234.210504 [8] Liu Yanqi, Liu Keyang, Tang Yunhai, et al. 100 TW optical amplifier based on Ti: sapphire splicing technology [J]. Chinese Journal of Lasers, 2021, 48(23): 204-205. (in Chinese) [9] Nabekawa Y, Kondo K, Sarukura N, et al. Terawatt KrF/ Ti:sapphire hybrid laser system [J]. Optics Letters, 1993, 18(22): 1922-1924. doi: 10.1364/OL.18.001922 [10] Mossavi K, Hofmann T, Szabo G, et al. Femtosecond gain characteristics of the discharge-pumped arf excimer amplifier [J]. Optics Letters, 1993, 18(6): 435-437. doi: 10.1364/OL.18.000435 [11] Nabekawa Y, Yoshitomi D, Sekikawa T, et al. High-average-power femtosecond KrF excimer laser [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2001, 7(4): 551-558. doi: 10.1109/2944.974226 [12] Zhao X Q, Liu J R, Yi A P, et al. Amplification of high power short pulse excimer laser with beam smoothing [J]. Optics and Precision Engineering, 2021, 19(2): 397-406. (in Chinese) doi: 10.3788/OPE.20111902.0397 [13] Ozharar S, Ozdur I, Quinlan F, et al. Jitter reduction by intracavity active phase modulation in a mode-locked semiconductor laser [J]. Optics Letters, 2009, 34(5): 677-679. doi: 10.1364/OL.34.000677 [14] Pi Y, Tian H, Li R, et al. Timing jitter and intensity noise characterization of a 122-MHz All-PM NALM mode-locked fiber laser [J]. IEEE Photonics Technology Letters, 2021, 33(24): 1439-1442. doi: 10.1109/LPT.2021.3125994 [15] Zvorykin V D, Ionin A A, Levchenko A O, et al. Ti: sapphire/KrF hybrid laser system generating trains of subterawatt subpicosecond UV pulses [J]. Quantum Electronics, 2014, 44(5): 431. doi: 10.1070/QE2014v044n05ABEH015442 [16] Ding M J, Li Xi Q, Huang L, et al. 100 kV repetition-rate high-voltage pulsed power supply [J]. High Power Laser and Particle Beams, 2012, 24(4): 179-182. (in Chinese) doi: 10.3788/HPLPB20122404.0929 [17] Saito T, Ito S, Tada A. Long lifetime operation of an ArF [J]. Applied Physics B Lasers & Optics, 1996, 63(3): 229-235. doi: 10.1007/BF01833791 -
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