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题名:
高效率高能量人眼安全全固态激光器技术研究
作者: 于真真
答辩日期: 2016
导师: 陈卫标
授予单位: 中国科学院上海光学精密机械研究所
学位: 博士
关键词: 全固态激光器 ; 人眼安全 ; Er:YAG ; 声光调Q ; 被动调Q
其他题名: Study of high-efficiency high-energy eye-safe all-solid-state laser
摘要: 1.5~1.6 μm激光光源具有人眼安全、处于大气窗口、相应探测器灵敏度高等优点,在激光雷达、遥感、主动成像等领域具有重要应用价值和前景。同带泵浦掺铒固体激光器作为一种直接获得人眼安全激光的新方法,近年来发展迅速。本论文主要基于距离选通三维成像激光雷达的应用需求,对半导体激光器同带泵浦的1.6 μm Er:YAG全固态激光器进行理论和实验研究。 论文首先介绍了1.5~1.6 μm人眼安全激光的应用背景和产生途径,并对同带泵浦掺铒固体激光器的研究进展进行了总结。阐述了铒离子的能级结构及其在不同基质中的光谱特性,重点介绍了Er:YAG晶体的特性,以及铒离子掺杂浓度对激光性能的影响。然后对掺铒固体激光器的准三能级特性进行研究,分析了增益介质的再吸收损耗、能量上转换损耗以及激发态吸收损耗的影响;分别介绍了Er:YAG晶体在1470 nm和1532 nm处吸收谱的特性,并分析两种波长泵浦光在高功率泵浦时由于基态耗尽效应导致的激光上能级储能的差别;通过端面泵浦CW Er:YAG激光器理论模型,分析了激光阈值及斜效率的影响因素,为后续激光器设计和实验研究提供理论参考。 针对成像激光雷达的应用需求,首先开展了1532 nm CW窄线宽半导体激光器同带泵浦的1617 nm Er:YAG固体激光器的研究。实验中采用低掺杂浓度的Er:YAG晶体减小能量上转换和再吸收等损耗,采用双Er:YAG晶体串联的方式提高激光输出功率和脉冲能量,采用腔内插入双标准具选模的方法实现窄线宽1617 nm激光输出。在激光器连续运转时,当入射泵浦功率为50.57 W,获得最高7.73 W 线偏振激光输出,光-光转换效率约为15.28%,输出激光中心波长和3 dB光谱宽度分别为1616.46 nm和0.044 nm。采用声光晶体进行调Q,在重复频率为500 Hz时,获得最高7.82 mJ单脉冲能量输出,脉冲宽度约为80 ns,相应的峰值功率约为97.75 kW。输出激光脉冲在x方向和y方向的光束质量因子分别为1.39和1.23。 为了获得更高的单脉冲能量输出,提出采用1470 nm 准连续半导体激光器同带泵浦Er:YAG激光器的方案,实现高效率高能量1617 nm激光输出。实验中同样采用了双低掺杂浓度Er:YAG晶体串联的方式实现高平均功率输出,采用U型谐振腔结构使系统结构紧凑,调Q方式同样为声光调Q。首先在腔内有标准具选模时,分析了自由运转下长脉冲能量输出和调Q模式下单脉冲能量输出随泵浦脉冲宽度的变化,发现提取效率随脉冲宽度的增加而降低,通过进一步分析光-光转换效率随泵浦脉冲宽度的变化,得到激光上能级储能寿命在5.2~5.5 ms。然后在腔内无标准具选模时,通过声光调Q,在泵浦脉冲宽度为5.5 ms 时,获得1617 nm最高20.54 mJ单脉冲能量输出,光-光转换效率(相对吸收泵浦能量)约为6%,重复频率为50 Hz,脉冲宽度为52 ns,相应的峰值功率约395 kW。输出激光的偏振消光比约为24 dB,在x方向和y方向的光束质量因子分别约为1.02和1.03,为近衍射极限输出。最后,完成了激光器样机的装调,样机输出激光参数为:最大单脉冲能量19.3 mJ,脉冲宽度约56 ns,峰值功率约344.6 kW。 为实现小型化、高效率的1.6 μm人眼安全激光光源,论文最后对同带泵浦的被动调Q Er:YAG激光器进行了研究。采用1532 nm CW半导体激光器为泵浦源,采用石英为基底的多层石墨烯作为可饱和吸收体。对连续运转的Er:YAG激光器,在入射泵浦功率为24.75 W时,获得1645 nm最高7.42 W功率输出,光-光转换效率约为30%。在被动调Q模式下,当入射泵浦功率为23.28 W时,得到单脉冲能量58.8 μJ、脉冲宽度4.21 μs、重复频率53.2 kHz的线偏振激光输出,输出激光的中心波长为1645.34 nm,3dB光谱宽度约为0.05 nm,光束质量因子分别为M2x=1.46和M2y =1.35。
英文摘要: 1.5~1.6 μm laser sources are eyesafe, in the atmospheric window and have high detector sensitivity. They have important value and prospect in numerous applications, including Lidar, remote sensing and active imaging. As a new method of direct generation of eye-safe laser, resonantly pumped erbium solid-state lasers(RPE) have developed rapidly in recent years. In this thesis, based primarily on the requirement of range-gated three-dimensional imaging Lidar, both theoretical and experimental investigations are undertaken on resonantly diode-pumped 1.6 μm Er:YAG all-solid-state laser. The application background of and different approaches to 1.5~1.6 μm eye-safe laser sources are introduced in the first place, and recent progress in RPE are reviewed. Then the energy level of Er3+ ions and its spectral characteristics in different hosts are presented. The properties of Er:YAG crystal are emphasized, as well as the effect of erbium doping concentration on laser performance. The following is the quasi-three-level character of erbium solid-state lasers, including reabsorption, energy-transfer-upconversion (ETU) and excited-state absorption (ESA) losses. The two strong absorption features in Er:YAG, one at 1532 nm and several near 1470 nm for resonant pumping are described, and the maximum pump inversion due to ground state depletion are analyzed for the two pumping bands. Moreover, based on a model of end-pumped CW Er:YAG laser, factors that influencing the laser threshold and slope efficiency are discussed, thus providing theorectical support for the following laser design and experimental investigation. With the application requirement of a three-dimentional imaging Lidar, a 1617 nm Er:YAG laser resonantly pumped CW 1532 nm narrow linewidth laser diodes (LDs) is investigated first. In the experiment, two low doping concentration Er:YAG crystals are adopted to reduce ETU and reabsorption losses, as well as to improve output power and pulse energy; Two etalons are inserted in the cavity to obtain narrow linewidth 1617 nm laser. For CW operation, the highest linearly-polarized output power of 7.73 W is achieved at 50.57 W incident pump power, with an optical to optical conversion efficiency of 15.28%. The central wavelength and 3 dB spectral width of the output laser are 1616.46 nm and 0.044 nm, respectively. Then an acousto-optical crystal is used for Q-switching. At 500 Hz pulse repetition frequency (PRF), pulses with a maximum energy of 7.82 mJ and pulse width of 80 ns are measured, and the corresponding peak power is 97.75 kW. The output beam quality were approximatly 1.39 and 1.23 in x and y directions, respectively. To obtain laser sources with much higher single pulse energy, a sheme of 1470-nm quasi-continuous wave LDs directly-pumped Er:YAG laser is proposed to achieve high-efficiency and high-energy 1617 nm laser. Also, two low doping concentration Er:YAG crystals are employed for output power and pulse energy scaling, a U-shape resonator for compact architecture and an acousto-optical crystal for Q-switching. With an intracavity etalon for mode selection, results of free running output and Q-switched output at different pump durations are analyzed; it is found that the extraction efficiency decreases as the pump durations increases, and further study of optical to optical conversion efficiency versus pump durations shows that the storege lifetime of the upper laser level is 5.2~5.5 ms. Without etalon in the cavity, Q-switched performance is studied. When the pump duration is 5.5 ms, a maximum pulse energy of 20.54 mJ at 1617 nm is obtained at 50 Hz PRF, with a pulse width of 52 ns, peak power of ~395 kW, and the optical to optical efficiency (relative to absorbed pump energy) of ~6%. The polarization extinction ratio of the output beam is about 24 dB, and the beam quality parameters are approximately 1.02 and 1.03 (diffraction limited). Besides, A laser prototype is completed, with a maximum pulse energy of 19.3 mJ, pulse width of 56 ns and peak power of 344.6 kW。 In order to develop compact, simple and high efficiency 1.6 μm eye-safe laser sources, a study of resonantly-pumped passively Q-switched Er:YAG is presented at the last but one section of the thesis. A CW 1532 nm LD is used for resonant pumping, and a few-laywe graphene on quartz for passive Q-switching. For CW operation, a highest 7.42 W output power of 1645 nm is measured when the incident pump power is 24.75 W, with an optical conversion efficiency of ~30%. In passive Q-switch regime, linearly-polarized ouput with pulse energy of 58.8 μJ, pulse width of 4.21 μs and pulse repetition frequency of 53.2 kHz is obtained at 23.28 W incident pump power. The central wavelength and spectral width of the output beam are 1645.34 nm and 0.05 nm, respectively. The beam quality factors at the maximum pulse energy are M2x=1.46 and M2y =1.35.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.siom.ac.cn/handle/181231/15949
Appears in Collections:学位论文_学位论文

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Recommended Citation:
于真真. 高效率高能量人眼安全全固态激光器技术研究[D]. 中国科学院上海光学精密机械研究所. 2016.
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