| 题名 | 高功率、高重频、高光束质量全固态皮秒激光器研究 |
| 作者 | 郭洁 |
| 文献子类 | 博士 |
| 导师 | 梁晓燕 |
| 关键词 | 全固态激光器 DPSSL 锁模激光器 Mode-locked lasers 掺钕钒酸盐晶体 Neodymium-doped vanadate laser crystals DP-Innoslab放大器 DP-Innoslab amplifier 寄生振荡抑制 Parasitic lasing suppression |
| 其他题名 | Studies on high-power all-solid-state picosecond lasers with high repetition rates and diffraction limited beam quality |
| 英文摘要 | 全固态皮秒激光器在可靠性和激光输出特性方面的不断提升使其在科研，工业、医学和军事等领域都得到广泛的应用，如生物成像、激光微纳制备、非线性频率转换、医学治疗和激光测距等。由于放大过程中通常不需要使用啁啾脉冲放大技术，皮秒激光器具有高效、稳定、紧凑、经济效益高等优点。与飞秒激光器相比，皮秒激光器在工业应用环境中以其成本和效益的良好均衡而显示了独特的优势。如今发展高功率高重复频率且具备良好光束质量的小型化全固态皮秒激光器具有重大的科学意义和应用价值。 目前，Nd3+离子掺杂的钒酸盐激光晶体以其优良的光学特性和机械性能以及可利用半导体激光器直接进行泵浦等优点，而成为可获得偏振输出的小型化全固态皮秒激光器的理想增益介质。高功率、高重复频率输出的皮秒激光器往往不易同时获得优异的光束质量，即难以同时兼顾高功率和高亮度的输出要求。为了研发出性能稳定，高功率，高光束质量的皮秒激光器以满足各种应用的需求，本论文针对振荡器的基模动态稳定腔优化设计和放大器中的寄生振荡抑制问题开展了基于Nd:YVO4和Nd:GdVO4晶体的高重复频率、高功率、高光束质量的皮秒激光系统的相关技术研究工作。取得的主要研究成果如下： 1、适用于不同输出功率范围的三种基模谐振腔设计方法。 对含有热透镜的谐振腔采用等效腔的方法模拟分析了影响模式大小及激光器稳区范围的相关因素，提出了适用于不同输出功率范围的三种基模谐振腔设计方法，为锁模振荡器的设计提供了理论依据。 2、新型σ偏振泵浦的高功率Nd:GdVO4振荡器。 创新性地提出了σ偏振泵浦的方法，使得激光晶体中的热梯度大大降低。充分利用该泵浦方法并结合Nd:GdVO4晶体良好的热特性，使得激光晶体所能承受的泵浦功率大大提高，并且进一步赋予基模谐振腔设计方案更大的自由度。结合σ偏振泵浦方案，我们采用Nd:GdVO4块状晶体搭建了一个高功率的被动锁模皮秒振荡器。在稳定的锁模运转下，该振荡器输出的最大功率为37 W，此时吸收的泵浦功率为73 W，对应51%的转化效率。实验中采用多种不同的输出耦合镜以优化输出情况，获得的脉冲宽度在11.2 ps和19.3 ps之间，光束质量均接近衍射极限，M2<1.05。实验结果验证这种新的σ偏振泵浦方法与我们的谐振腔设计方案二者之间的有机结合能够实现高泵浦功率下输出效率和光束质量之间十分优异的平衡，对于高功率振荡器的设计具有重要的指导意义。这是目前报道的基于该晶体的振荡器获得的最高输出功率。 3、一种新型的抑制寄生振荡的DP-Innoslab放大器。 该方案提出了一种新的分立路径法（DP-Innoslab）来消除Innoslab放大器中的寄生振荡效应并且很好地抑制了放大的自发辐射（ASE）。传统的Innoslab放大器中，由快轴方向互相平行的反射腔镜所控制的几通光束在进行放大时全部分布在同一平面内，高增益特性往往导致寄生振荡的产生，通常需要借助种子光的注入才能进行抑制。我们的新技术方案使得Innoslab放大器中的几通光束分布在几个分立的平面内，快轴方向没有任何两个反射镜之间互相平行，寄生振荡效应得到了很好的抑制，从而Innoslab放大器具有的高增益特性和均匀的增益分布得以保留。在该技术方案下，即使在没有种子光注入的情况下也没有寄生振荡发生。基于Nd:GdVO4晶体，我们得到了99 W，12.4 ps，81 MHz的TEM00模输出，放大器的能量抽取效率为42%，并且很好地保持了振荡器优异的光束质量，光束质量因子测量结果为M2 x=1.09和M2 y=1.07。实验结果证明DP-Innoslab放大器能够实现高提取效率和衍射极限的光束质量。这是目前已知报道中基于Nd:GdVO4晶体获得的皮秒量级的最高输出功率。 4、高光束质量高重复频率Nd:GdVO4振荡器。 采用基模谐振腔方法，设计了优异的模式匹配腔型，获得了近衍射极限光束质量的高重频Nd:GdVO4振荡器。实验中采用非偏振泵浦的方式，在最大吸收泵浦功率19.7 W的条件下得到了10.8 W的最大输出功率，输出的锁模脉冲重复频率为56 MHz，脉冲宽度16.1 ps，两个方向的光束质量因子M2均为1.02。实验验证了我们的基模谐振腔设计方案在优化锁模特性方面的可行性及灵活性。该结果是目前报道的非偏振泵浦条件下基于单个块状Nd:GdVO4晶体的皮秒振荡器获得的最高输出功率。 5、高光束质量微焦量级输出的Nd:YVO4振荡器。 基于端面泵浦的Nd:YVO4晶体和MPC腔延长腔长，利用SESAM进行被动锁模，获得了单脉冲能量微焦量级的皮秒振荡器。在吸收泵浦功率13.9 W、输出透过率30%的条件下，实现了8.3 W的连续锁模（CWML）输出，输出的脉冲重复频率为63.8 MHz，对应单脉冲能量为130 nJ。进一步以保Q型的MPC腔插入谐振腔中，在保持腔内的激光模式不变的情况下，增大输出的单脉冲能量。通过优化MPC腔，得到了平均功率6.7 W、重复频率6.3 MHz、单脉冲能量1.1 μJ且脉冲宽度16.4 ps的连续锁模脉冲输出。其两个方向的光束质量因子均不大于1.1。 6、新型晶体 Nd,Y:SrF2激光性能研究。 基于两种掺杂浓度的新型晶体Nd,Y:SrF2，在793 nm的半导体激光器泵浦下，获得1056.9 nm的输出。掺杂浓度为0.43 at.%的晶体样品在2.2 W的泵浦功率下获得的最大输出功率为1.0 W。相应的斜效率为53%。掺杂浓度0.15 at.%的晶体样品在吸收泵浦功率1.5 W的情况下获得464 mW的输出功率，斜效率为36.1%。改进的腔型在提高了输出效率的同时也获得了良好的光束质量。波长调谐范围为1049.7 nm-1059.1 nm。实验验证了该晶体优良的激光性能。; All-solid-state picosecond oscillators and amplifiers have significant applications in scientific research, industry, medicine and military thanks to its enhancement in reliability and output performance. These applications include biological microscopy, laser micro-nano processing, nonlinear frequency conversion, medical treatment and laser ranging. Free from chirped-pulse amplification in normal conditions, current picosecond lasers are highly efficient, durable, compact and low-cost. Compared with femtosecond lasers, picosecond lasers are well adapted to the industrial environment because of its better tradeoff between cost and benefit. Nowadays, compact all-solid-state picosecond lasers with high average power and high repetition rates, combined with excellent beam quality, are highly needed in scientific research fields and other applications. With excellent optical and mechanical properties and capacity of being conveniently pumped with laser diodes, neodymium-doped vanadate laser crystals have become the most ideal series of gain medium for compact solid-state lasers with linearly polarized output. All-solid-state picosecond lasers with high average power and high repetition rates always have difficulties in obtaining high beam quality at the same time. In order to develop all-solid-state picosecond lasers with high average power and high beam quality for diverse applifcations, systematic studies based on Nd:YVO4 and Nd:GdVO4 have been carried out. Solutions to dynamically stable resonators with fundamental mode output in oscillators and the problem of parasitic lasing suppression is targeted. The main results in this dissertation have been summarized as follows: 1. Analysis of three kinds of dynamically stable resonators with fundamental mode output for different power level Resonators containing a focusing thermal lens are investigated by modified cavity parameters of those without lenslike medium. Factors related to mode size and stability zones are analysed. Basic principles about dynamically stable resonators with fumdamental mode is specially described. Three schemes of resonator configration for different power level is proposed. Further step-by-step upgrades of oscillators are based on these principles and analysis. 2. High power, diffraction limited picosecond oscillator based on Nd:GdVO4 bulk crystal with σ polarized pumping With the new scheme of σ polarized in-band pumping, a high power passively mode-locked picosecond oscillator based on Nd:GdVO4 crystal was demonstrated. Thermal gradient and thermal aberration was greatly decreased with the proposed configuration. Combined with the superior thermal performance of Nd:GdVO4, the maximum pump power applied to the crystal is greatly enhanced. Meanwhile, more freedom is endowed with the resonator designing. Maximum output power of 37 W at 81 MHz repetition rate with 19.3 ps pulse duration was achieved directly from Nd:GdVO4 oscillator, corresponding to 51% optical efficiency. The oscillator maintained diffraction limited beam quality of M2 < 1.05 at different output coupling with pulse durations between 11.2 ps to 19.3 ps. Excellent thermal management was achieved with σ polarized in-band pumping and excellent mode matching condition was obtained. As a result, efficiency and beam quality are favorably balanced. To the best of our knowledge, this is the highest output power of picosecond oscillator based on single Nd:GdVO4 bulk crystal. 3. A novel DP- Innoslab amplifier for parasitic lasing suppression We propose a technique for eliminating self-lasing and suppressing amplified spontaneous emission in partially pumped slab amplifier with discrete path configuration. Current Innoslab design mainly counts on the seeding injection to suppress self lasing. Limitation exists with the above technique, especially in amplifier systems with very high gain coefficient, where self lasing might still exist with powerful seeding. Compared to typical Innoslab amplifier where all the passes are in the same plane, several discrete planes exist in DP-Innoslab amplifier. Since all the cavity mirrors are not parallel to each other, spontaneous emission would be ejected out of the pumping zone after several bounces. Therefore, energy extraction by ASE is significantly decreased, and parasitic lasing could hardly build up. High gain character and homogeneous gain distribution were well preserved with the proposed scheme. Based on Nd:GdVO4 crystal, a 99 W, 12.4 ps, TEM00 laser output was achieved with 42% extraction efficiency. Diffraction limited beam quality remained undisturbed after amplification with M2 x = 1.09 and M2 y = 1.07 in the orthogonal directions. To the best of our knowledge, this is the highest picosecond output power in Nd:GdVO4 lasers. 4. Diffraction limited Nd: GdVO4 oscillator with high repetition rate Basd on the principles about dynamically stable resonators, a well mode matching cavity is designed. In this experiment, unpolarized pumping method was adopted. A maximum CW mode-locking laser output power of 10.8 W was achieved at 19.7 W absorbed pump power and output coupling of 17%. The repetition rate is 56 MHz with a pulse duration of 16.1 ps. The oscillator maintained diffraction limited beam quality of M2 =1.02 in the orthogonal directions. These performances indicate the feasibility and flexibility of our resonator designing scheme. 5. Nd:YVO4 oscillator with 1 μJ pulse energy A passively mode-locked picosecond oscillator with end-pumped Nd:YVO4 crystal combined with SESAM and multi-pass cell (MPC) has been demonstrated. A maximum CW mode-locking (CWML) laser output power of 8.3 W was achieved at 13.9 W absorbed pump power and output coupling of 30%. The repetition rate is 63.8 MHz and a pulse energy of 130 nJ. It was a practical method for Herriott-style multi-pass cell to extend the overall cavity path length and reduce the repetition rate of pulses, while maintaining laser cavity mode and improving the output pulse energy. With a MPC inserted into the laser cavity, the output pulse energy increased to be 1.1 μJ with a pulse width of 16.4 ps at 6.3 MHz, amounting to output average power of 6.7 W. The beam quality factor in both directions are better than 1.2. 6. Investigations on laser performance of diode-pumped Nd, Y-codoped:SrF2 single crystals The laser performances of Nd, Y:SrF2 crystals are demonstrated with Nd3+ concentrations of 0.15 at.% and 0.43 at.%. The sample with 0.43 at.% Nd3+ concentration yields a maximum output power of 1.0 W at 1056.9 nm with a slope efficiency of 53%. For the 0.15 at.% Nd3+-doped crystal sample, the maximum output power is 464 mW at 1056.9 nm, with a slope efficiency of 36.1%. Diffraction limited beam quality is achieved in the orthogonal directions with the improved cavity design. The wavelength is tuned within the range of 1049.7 nm to 1059.1 nm. These results indicate that Nd, Y:SrF2 is a promising candidate for all-solid-state lasers. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31016]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 郭洁. 高功率、高重频、高光束质量全固态皮秒激光器研究[D]. |
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