基于键合激光晶体的高效、高峰值功率、皮秒径向偏振固体激光器研究

Contineously-wave high-power,or high-peak-power pulsed laser with radial polarzation finds application in many fields like the efficient metal processing, particle manipulation and super-resolution microscopy and others. Previously we conducted the research on laser-diode (LD) end-pumped, radially polarized microchip laser by using a photonics crystal grating as polarization-selective output coupler, wherein the thermal lens effect in the microchip gain medium became serious and the laser output decreased with the pump power at high pumping level. ..In this research, we concentrate on the following two aspects. Firstly, we will theoretically and experimentally investigate the LD end-pumped, radially polarized composite-structure laser of YAG+Nd:YAG+YAG crystal by using a photonics crystal grating s polarization-selective output coupler, in which the composite-structure laser crystal will be efficient in removing the heat deposited in the gain medium and thus thermal lens effect becomes negilible. As a result, the highly efficient, high-power and radially polarized could be expected. Furthermore, we will theoretically and experimentally investigate the LD end-pumped, radially polarized, passively-Q-switched and composite-structure laser of YAG+Nd:YAG+Cr4+:YAG crystal with a photonics crystal grating used as polarization-selective output coupler. It is expected the composite-structure laser crystal will be efficient in removing the heat deposited in the gain medium and also shorten the cavity length of laser considerably, therefore the radially polarized pulse with peak power larger than 30kW and picosecond duration could be anticipated from this laser.

连续输出的高功率、及高峰值功率短脉冲输出的径向偏振激光器在高效金属加工，微粒子操控、超分辨显微等领域有重要应用前景。申请人在前期工作中研究的基于光子晶体光栅镜的径向偏振微片激光器由于存在热透镜效应，在较大泵浦功率情况下径向偏振输出功率反而减少，这限制了LD端面泵浦的径向偏振微片激光器的发展和应用。本研究可分为两个部分的内容。首先我们将理论和实验研究LD端面泵浦的基于键合晶体YAG+Nd:YAG+YAG和光子晶体光栅的高效高功率径向偏振固体激光器，力争通过键合结构克服端面泵浦固体激光器中热透镜效应，从而获得高效高功率径向偏振输出；其次我们将理论和实验研究LD端面泵浦的基于键合晶体YAG+Nd:YAG+Cr4+:YAG和光子晶体光栅的被动调Q径向偏振固体激光器，通过采用键合的增益晶体来消弱其中的热透镜效应并有效缩短激光腔程度，从而期望获得峰值功率大于30kW的皮秒宽度的径向偏振脉冲输出。

1. 实验利用YAG/Nd:YAG/Cr4+:YAG 键合晶体和光子晶体光栅镜获得高峰值功率和高光束质量的被动调Q 径向脉冲激光输出，激光器的输出功率达到435 mW，斜率效率为14.7%。在吸收抽运功率为6.8 W 时，输出激光脉冲的峰值功率达到15.7 kW，脉冲能量达到50.1 mJ，脉冲宽度为3.2 ns，重复频率为8.1 kHz，径向偏振纯度为95.8%。.2. 利用粗芯径、大数值孔径的多模光纤作为模式转换器件，首次提出了通过离焦耦合调节将激光二极管输出光束转换为空心光的机制。首先，利用多模光纤转换得到的空心光泵浦 Nd:YAG 激光器，在没有任何腔内偏振选择元件的条件下，实现了径向偏振激光输出。对环形光泵浦的 Nd:YAG 激光器输出径向偏振光的机理进行分析，发现激光晶体中存在的热致双折射会导致径向偏振光和角向偏振光与环形泵浦光的空间重叠效率存在差异；其次，通过在腔内插入可饱和吸收体 Cr4+:YAG，实现了径向偏振的脉冲激光输出；最后，通过在腔内插入声光调 Q 开关，实现了主动调 Q 脉冲激光输出，输出激光为线偏振的 LG01 模。.3. 首次提出并实验实现了磁悬浮的旋转盘片激光器。以 Nd:YAG 晶体薄片作为激光增益介质，利用 LD 端面泵浦的结构，在 4 Hz 转动速率下，实现了 17.7 mW 的 TEM00 单模激光输出，并且通过对比不转的情况，验证了晶体转动对激光器输出光束亮度的提高作用。.4.申请国内发明专利8项,已授权3项； .5. 发表SCI论文16篇, 中文EI论文2篇；.6. 课题组成员参加国际会议7次，国内会议8次，国际合作与交流5次；.7. 形成一支径向偏振光纤激光器的专业研究团队，目前研究队伍中助理研究员一名，在读硕士研究生5名，在读博士研究生2名，已毕业硕士研究生7名，毕业博士生3 名。