高功率高重频腔倒空式全固态超快激光器研究
文献类型：学位论文
| 作者 | 高鹏 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 梁晓燕 研究员 |
| 关键词 | 全固态激光器 锁模激光 Nd离子掺杂晶体 腔倒空 多通腔 再生放大器 |
| 其他题名 | Research on high-power cavity-dumped all-solid-state ultrafast lasers with high repetition rates |
| 中文摘要 | 高功率、半导体激光泵浦的全固态超快激光器由于其结构紧凑、效率高、峰值功率高等优势在工业、医药和科研等众多领域有着广泛和重要的应用，如生物物理学、化学光谱仪、非线性光学和微加工等。另外，更高的重复频率意味着更短的加工时间，在工业和生物医药等微加工方面也是所需要的。与飞秒激光相比，皮秒脉冲以其低成本、高稳定性、小的热加工区域和对材料的低损伤等在高精度的材料加工上显示了其独特的优势。因此，脉冲能量微焦、重复频率MHz量级的皮秒激光系统得到了很大的关注。 Nd离子掺杂的晶体由于其大的吸收系数和发射截面、相对较宽的增益带宽和高离子掺杂浓度等优点，被认为是集成化的全固态激光器的理想增益介质。以掺杂Nd离子的晶体作为增益材料、结合被动锁模的元件SESAM，可用于搭建产生稳定皮秒脉冲的激光器。但是从一个锁模振荡器直接产生的脉冲能量一般较低，在纳焦量级，限制了其在科学和工业等领域上的应用。而腔倒空技术能够在保持激光系统紧凑的条件下，在单个谐振腔内实现脉冲能量微焦、重复频率MHz量级的激光脉冲输出。 本论文基于Nd离子掺杂的主要晶体如Nd:YVO4，Nd:GdVO4和Nd:LuVO4晶体，进行高功率、高重频腔倒空式全固态超快激光器的研究。这类激光系统中，没有任何脉冲展宽和压缩元件，可有效地减少系统的复杂程度且提高整体的稳定性。取得的主要研究成果如下： 1.基于双Nd:YVO4晶体、SESAM被动锁模的腔倒空式皮秒振荡器。在总泵浦功率46 W、耦合透过率14%的实验条件下，实现了19 W的连续激光（CW）输出。保Q型的MPC腔可有效地延长整个谐振腔的腔长、降低谐振腔的重复频率，同时在保持腔内的光斑模式不改变的情况下，增大脉冲能量的输出。通过设计合适的MPC腔，得到了平均功率12 W、重复频率7.24 MHz、脉冲宽度8.4 ps的连续锁模（CWML）输出。同时结合腔倒空技术，最终获得了重复频率为100 kHz、脉冲能量为16.2 μJ、脉冲宽度为8.4 ps的超快激光输出。输出的脉冲通过聚焦后用于烧蚀白宝石片，结果表明腔倒空式的皮秒振荡器在微加工领域具有很高的应用前景。且由于其输出的脉冲能量较高，可直接作为能量放大系统的种子源。 2.基于Nd:GdVO4晶体腔倒空式被动锁模的皮秒振荡器。在晶体总吸收功率42 W的条件下，实现了28 W（CW）和23 W（CWML）的激光输出。通过MPC腔延长腔长，实现了平均功率19 W、重频8.1 MHz、脉冲宽度8.94 ps的大能量脉冲激光输出。在腔倒空阶段，在300 kHz时最大的脉冲能量为34.7 μJ；1 MHz时脉冲能量为16.22 μJ，其脉宽分别为7.0 ps和8.55 ps，是当时已报道的腔倒空式锁模激光系统输出的最高的脉冲能量和平均功率。同时，构造一个理论模型分析SESAM被动锁模的腔倒空系统的动态演化过程。且更高的脉冲能量输出有望通过优化MPC腔反射率、合适的泵浦条件及倒空频率来达到。 3. 基于Nd:LuVO4晶体、SESAM被动锁模的腔倒空式皮秒振荡器。在晶体总吸收功率44 W的条件下，实现了31.6 W（CW）和28 W（CWML）的激光输出。通过插入MPC腔，实现了平均功率24 W、重频12.1 MHz、脉冲宽度5.5 ps的激光脉冲输出。在腔倒空的条件下，重复频率分别为300 kHz、600 kHz、1 MHz和1.5 MHz时，分别获得了40.7 μJ (12.2 W)、29.3 μJ (17.6 W)、20 μJ (20 W)和14.3 μJ (21.4 W) 的脉冲能量。而在300 kHz时，脉冲宽度最窄，为4 ps。这是当时已报道的Nd:LuVO4晶体振荡器输出的最高的脉冲能量和平均功率，实验证明了Nd:LuVO4晶体作为高功率全固态激光器增益介质的优秀潜质。 4.基于Nd:LuVO4晶体，搭建了目前已报道的首台半导体泵浦的、高功率超快再生放大系统。其工作频率高达1.43 MHz，是目前已知的皮秒再生放大系统中最高的重复频率。首次利用MPC腔技术提高种子源激光的脉冲能量，以抑制高重频再生放大器的脉冲多周期性的现象。在1.43 MHz时，获得了最高25.1 W的平均功率，其对应的脉冲能量为17.6 μJ。而在100 kHz时，获得了最大的脉冲能量为205 μJ ，其对应的功率为20.5 W。对比晶体的总吸收功率可知，再生放大系统的总转换效率高于45%。由于一定的增益窄化效应，脉冲宽度由入射脉冲的5.1 ps变为出射脉冲的8.9 ps。且由于高重频时增益降低，脉冲宽度由100 kHz的8.9 ps变化为1.43 MHz的7.0 ps。该高功率、高重频、高效率且输出光斑质量良好的皮秒再生放大系统可作为高精度微加工理想的超快激光光源。 实验表明，Nd离子掺杂的Nd:YVO4，Nd:GdVO4和Nd:LuVO4晶体都可作为高功率LD泵浦的全固态皮秒激光器理想的增益介质。与其他两块晶体相比，Nd:LuVO4晶体具有更大的吸收和发射截面，其增益线宽也相对较宽。因此，腔倒空式锁模的Nd:LuVO4晶体振荡器得到了更大的脉冲能量和更窄的脉冲宽度输出。而对基于Nd:LuVO4晶体的再生放大和腔倒空系统进行类比，再生放大系统可输出更高的脉冲能量，但是其装置体积相对较大。而腔倒空式系统可以输出相当的脉冲能量，同时还能保持一定的系统紧凑性。由于其具有高功率、高重频的脉冲能量输出，两种系统都可以作为材料微加工良好的激光光源。 |
| 英文摘要 | High-power diode-pumped solid-state lasers (DPSSLs) with ultrafast pulses have been widely and significantly used in industry, medicine and scientific research etc., including biophysics, chemical spectroscopy, nonlinear optics and microfabrication because of their compactness, high efficiency, and high peak power. Moreover, a higher possible repetition rate is also required for some applications, such as micromachining in industry and biomedicine, which result in short processing times. Compared with femtosecond lasers, picosecond pulses are well suited for material machining with high precision, because of their unique advantages of low cost, high stability, small heat-affected zone and extremely little damage. Therefore, picosecond laser systems with microjoule-regime pulse energies and megahertz repetition rates have drawn extensive attention. The Nd-doped crystals which have large absorption coefficient and stimulated emission cross section, relatively broad gain bandwidth and high Nd3+ doping level, have been proved to be good gain materials for compact DPSSLs. Ultrashort DPSSLs based on Nd-doped materials that are passively mode-locked with semiconductor saturable absorber mirror (SESAM) have been used to obtain a reliable oscillator of picosecond pulses. However, pulse energy that directly originates from a mode-locked oscillator is relatively low, usually at nJ-level, which limits its applications in scientific and industrial areas. Cavity dumping is an efficient method to generate high pulse energies in the microjoule range with MHz-level repetition rates, while maintaining comparable compactness to contain a single resonator. In this dissertation, we focus on the research on the cavity-dumped all-solid-state ultrafast lasers with high repetition rates based on Nd-doped gain materials such as Nd:YVO4, Nd:GdVO4 and Nd:LuVO4. These systems could maintain moderate compactness since they do not require any pulse stretching and compression, which adding the overall complexity and reducing their efficiency. The main work and the main results in the thesis are summarized as follows: 1. A dual Nd:YVO4 crystal SESAM passively mode-locked with cavity dumping picosecond oscillator has been demonstrated. It was a useful method for Herriott-style multi-pass cell (MPC) to extend the overall cavity path length and reduce the pulse repetition rate, while maintaining laser cavity mode and improving the output pulse energy. A maximum continuous-wave (CW) laser output power of 19 W was obtained at a total output coupling of 14% and a total pump power of 46 W. A maximum CW mode-locking (CWML) laser output power of 12 W was achieved with the same pump power and output coupling, mode-locking at 7.24 MHz, and a pulse width of 8.4 ps with a MPC inserted into the laser cavity. During cavity-dumped operation, the output pulse energy increased to be 16.2 μJ with a pulse width of 8.6 ps at 100 kHz. The output pulses were focused to ablate a white sapphire and the results confirmed the potential application of the cavity-dumped oscillator in micromachining. Furthermore, the oscillator can be used as an amplifier system seed resource for energy scaling because of its high pulse energy. 2. A passively mode-locked with cavity dumping picosecond oscillator based on Nd:GdVO4 crystals has been demonstrated. Maximum CW and CWML laser output power of 28 and 23 W were obtained under an absorbed pump power of 42 W, respectively. With a MPC inserted into the cavity, an output power of 19 W was achieved, mode-locking at 8.1 MHz, with a pulse width of 8.94 ps. For cavity-dumped operation, we obtained the maximum pulse energy of 34.7 μJ at 300 kHz, and 16.22 μJ (16.22 W) at 1 MHz, with pulse widths of 7.0 and 8.55 ps, respectively. To the best of our knowledge, it was the highest pulse energy and highest average power reported from picosecond cavity-dumped mode-locked oscillator. Meanwhile, a theoretical model was investigated to describe the dynamic of a cavity-dumped SESAM mode-locked laser. It can be anticipated that, in further experiment, through higher reflectivity of MPC, appropriate pump power and suitable dumping rates, pulses with higher energy could be obtained. 3. A SESAM passively mode-locked Nd:LuVO4 oscillator with cavity dumping has been demonstrated. Under an absorbed pump power of 44 W, maximum CW and CWML laser average power of 31.6 W and 28 W were obtained, respectively. With a MPC inserted into the cavity, an output power of 24 W was achieved, mode-locking at 12.1 MHz, with a pulse width of 5.5 ps. Pulse energies of 40.7 μJ (12.2 W) at 300 kHz, 29.3 μJ (17.6 W) at 600 kHz, 20 μJ (20 W) at 1 MHz and 14.3 μJ (21.4 W) at 1.5 MHz were presented in cavity-dumped operation. Meanwhile, the shortest pulse duration of 4 ps was obtained at 300 kHz with a sech2-fit. To the best of our knowledge, this is the highest pulse energy and highest average power yet reported from a Nd:LuVO4 oscillator. This study confirms that Nd:LuVO4 has great potential for developing diode-pumped high pulse energy lasers. 4. A compact diode-pumped, high-power regenerative amplifier (RA) laser system based on Nd:LuVO4 crystal with picosecond pulses has been reported for the first time to our knowledge. The operating repetition rate was up to 1.43 MHz, which was the highest rate in the picosecond RA regime. A MPC was firstly used to improve the pulse energy of seed laser to suppress the complex pulse energy dynamics or even bifurcations and maintain the compactness of the RA system. At the maximum repetition rate of 1.43 MHz, an average output power of 25.1 W was obtained, corresponding to a pulse energy of 17.6 μJ. The maximum pulse energy of 205 μJ was achieved at 100 kHz with an average power of 20.5 W. Compared with the absorbed pump power of crystals, the overall efficiency of RA system was higher than 45%. Due to moderate gain narrowing, the injected pulses with pulse duration of 5.1 ps broadened to 8.9 ps during amplification. Moreover, pulse width was reduced from 8.9 ps at 100 kHz to 7.0 ps at 1.43 MHz because of lower gain in the higher repetition rate. The high-power, high repetition rate picosecond RA system with good beam qualities could be used as the excellent source for high precision materials processing with high efficiency. Our experiments have shown that Nd-doped crystals of Nd:YVO4, Nd:GdVO4 and Nd:LuVO4 could be used as the ideal gain materials for high power, diode-pumped solid-state picosecond lasers. Compared with two other crystals, the Nd:LuVO4 has an even larger absorption cross section and emission cross section, a relatively broader gain linewidth. As a result, cavity-dumped mode-locked Nd:LuVO4 oscillator has obtained a higher pulse energy output and a shorter pulse width. Compared with RA and cavity-dumped system based on Nd:LuVO4 crystal, the RA regime has a higher output pulse energy, but it has a relatively larger setup size. Meanwhile, cavity-dumped mode-locked oscillator could achieve moderate output energy and maintain compactness of the system. However, they all could be used as the excellent laser source for materials micromachining because of its high-power, high repetition rate output pulses. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15960]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 高鹏. 高功率高重频腔倒空式全固态超快激光器研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。