2μm波长范围OPCPA系统用Tm:Ho:YCOB晶体研制

The Ultrafast pulse in the 2-µm spectral range has become a hot research area because of its wide applications in medical treatment, laser remote sensing, laser radar etc. Additionally, it is also the foundation to obtain the mid-infrared femtosecond laser by the SPOPOP technique. This project will be to demonstrate the feasibility of the OPCPA system based on a novel seed laser sources in the 2-μm spectral range. The main objective will be to fill the gap in the 2-µm spectral range where short and ultrashort pulse solid-state lasers have shown only unsatisfactory performance or simply do not exist. With the Tm3+ and Ho3+ co-doped in the laser media, the tunable laser operation in the 2-μm spectral range can be achieved. The broad absorption and fluorescence spectra of the disordered crystal thus favor efficient diode pumping and ultrashort pulse generation. Additionally, compared with glass, the disordered crystal can also be used in the high power system because of the high thermal conductivity. The absorption and emission spectra of the Tm3+, Ho3+ co-doped YCOB crystal will be strongly inhomogeneously broadened due to the disordered lattice. The broad spectrum features a very efficient pumping and the production of ultrashort pulse. Characterization on Tm:Ho:YCOB crystal quality, thermal properties，optical properties and laser performance were carried out. The main objective will be to fill the gap in the 2-µm spectral range, to which it is a foundation for its practical application.

2μm波段超短脉冲因其是获得同步泵浦光参量振荡输出中红外飞秒激光的基础，同时在医学治疗、激光遥感和激光雷达等领域显示出广泛的应用而成为国内外的研究热点。本项目是基于2µm附近OPCPA系统，开发新的2 µm波段附近的种子光源来填补超短脉冲在2µm 波段的空白和不足。通过Tm3+和Ho3+共掺杂的激光介质，可以获得2μm波长的激光。无序晶体具有宽的吸收光谱和发射光谱，既有利于二极管泵浦，又有利于锁模脉冲产生；同时具有高的热导率，适合在大功率系统中应用。YCOB晶体结构具有一定的无序性，将Tm3+和Ho3+掺杂入YCOB晶体，通过非均匀加宽效应，可以进一步增宽晶体的发射波长范围，更有利于超短脉冲激光的产生。本课题拟采用提拉法生长Tm:Ho:YCOB晶体，并对其物理性能、2μm波段连续、脉冲和超短脉冲进行系统研究，将晶体生长、晶体物理及激光器优化设计相结合，为其实用化奠定基础。

超快激光技术的应用涵盖了物理学、工程学、化学、生物学、医学、等诸多领域，其在高分辨光谱学、多光子成像、微加工、激光矫正、粒子加速、高能X 射线生成及惯性约束聚变等方面有着广泛的用途。啁啾脉冲放大技术（OPCPA）是目前获得超快激光最为行之有效的方法。运用基于连续可调种子光源和非共线作用的OPCPA 技术已经可以在波长范围600-1500nm 之间获得最短脉冲短至4fs，最高功率至PW 量级的超快脉冲激光。但是在2μm波段超短脉冲的研究还处于起步阶段，考虑到2μm 波段超短脉冲是获得同步泵浦光参量振荡（SPOPOP）输出中红外飞秒激光的基础，同时在医学治疗、激光遥感和激光雷达等领域显示出广泛的应用，我们决定开展该方面的工作。本项目是基于2μm 附近OPCPA 系统，开发新的2 μm 波段附近的种子光源。我们基于上述研究目的，开展了Tm:YCOB和Tm,Na:CNGG两种晶体的生长与超短脉冲研究。我们成功生长了上述两种晶体，并对其基本性能，包括结构、热学、光谱及激光等进行了系统表征。并在Tm,Na:CNGG晶体中通过被动锁模技术，采用碳纳米管为可饱和吸收体，成功实现了2μm波段超短脉冲激光输出，脉冲宽度为84fs，输出功率22mW，重复频率90 MHz。据我们所知，该结果是目前晶体在2μm波段中所实现的最短脉冲激光。