基于非线性切伦科夫辐射产生中红外超短脉冲机理与实验研究

We propose in this project a new nonlinear frequency conversion through optical Cherenkov radiation to produce the energetic ultra-short mid-IR pulses by pumping the available long pulsed laser output in the nonlinear media. The advantage of this approach is quite simple but powerful. The generation of ultra-short mid-IR radiation and its interaction with the nonlinear crystals and semiconductors has been the important research hot because of the fundamental and creative motivation. We will investigate the soliton compression of few-cycle pulses in the normal dispersion regime of the nonlinear second-order crystals and semiconductors and the mechanism of optical Cherenkov radiation and the experiments of achieving the ultra-short mid-IR pulses. We will also present the comprehensive model for the description of femtosecond pulses propagating in the nonlinear media and the phase-matching requirement for mid-IR generation and the optimization of the output efficiency of the optical Cherenkov radiation and the wavelength tuning（2－5 um）via quasi-phase-matching structure as well. The amplification and the compression of mid-IR generation are also considered. Finally we will focus on this approach to realize the nonlinear frequency conversion to mid-IR ultra-short pulses based on the optical Cherenkov radiation by using the stable fiber lasers as pumps.

本项目研究基于光学切伦科夫辐射机理的一种新型非线性频率变换技术，旨在利用目前可获得的长脉冲激光输出，实现中红外波长超短脉冲输出的简单而有效的新方法。本项目探索的中红外波段超短脉冲产生及与物质相互作用，已经成为现代科学的重要研究前沿领域，具有很强的基础性与创新性。研究内容包括在非线性晶体和半导体材料的正常色散区获得周期量级超短脉冲孤子压缩过程，通过非线性光学切伦科夫辐射在反常色散区实现中红外超短脉冲产生，研究切伦科夫辐射的产生机理与实验验证；通过对飞秒脉冲在非线性介质的非线性传输模型精确模拟，获得中红外脉冲产生条件、输出效率优化和利用准位相匹配结构开展可调谐中红外波段（2－5um）飞秒激光脉冲产生、放大与压缩的新方法；基于稳定性高的光纤激光器作为泵浦，利用非线性切伦科夫辐射产生中红外超短脉冲，探索实现高效非线性频率转换的一个新途径。

本项目研究了宽带非线性光学切伦科夫辐射机理，揭示了基于相位匹配和群速度匹配条件可以实现孤子隧道效应。创新性地将孤子隧道效应理解为孤子态耦合现象，实现高效宽带孤子切伦科夫辐射；基于孤子隧道效应的非线性光学切伦科夫辐射，提出了一种新颖的非线性光波频率转换方法。研究了光学孤子与切伦科夫辐射相互作用过程来类比孤子视界效应，成功演示了基于光孤子行为的全光操作手段，实验上观察到切伦科夫辐射绝热和级联多次反射过程，依靠切伦科夫辐射在时域上与双孤子碰撞后群速度发生变换，实现切伦科夫辐射波长往返转换，为全光操控提供可能。研究回音壁模式谐振腔中时域耗散孤子切伦科夫辐射动力学过程和暗孤子激发过程，通过微腔色散管理同样可以有效调控微腔耗散孤子及光学频率梳，证实微腔孤子切伦科夫辐射可以有效提高微腔频率梳的稳定性，对光频梳应用具有重要意义。在非线性波导中实现单周期超短脉冲及超连续产生；在周期性极化晶体中通过调节极化周期实现了可调谐中红外脉冲的输出，丰富和拓展了超快非线性光学在集成波导光学和全光通信系统中的应用。发表学术期刊论文13篇（基金标注），参加国际会议7次，培养研究生5名。