长波中红外（8微米）周期量级超快光场的产生与操控技术研究

It has become difficult for traditional Ti:sapphire ultrafast lasers to accommodate the future scientific frontiers such as high-order harmonic generation and attosecond science. By following the project instruction, we will push the research activity of manipulating ultrafast light fields from near-infrared region (3 μm) to the currently inaccessible mid-infrared region (5 μm). However, present mid-infrared ultrafast lasers have challenged by three limitations in amplification bandwidth, parametric gain and dispersion management, and also suffered from the thermal problem in high-average-power OPCPA. Because of these challenges and problem, it is necessary to develop a new family of technologies for the parametric systems with non-oxide crystals. In the first phase of our project, we will study a new phase-matching scheme that is insensitive to both wavelength and temperature, and a new design criteria that enables a same pulse duration of the idler to that of the pump. In the second phase of our project, we will explore a new technical route of converting near-infrared multi-cycle pulses to mid-infrared (8 μm) few-cycle pulses, which is capable of simultaneously delivering a high repetition-rate (1kHz), a high peak-power (10GW), an extreme duration (<3 cycles), and a stable CEP performance. In addition, we will further study the manipulation of few-cycle and sub-cycle light fields based on the technique of soliton pulse compression. Finally, our proposed project is of importance to a broad fields such as ultrafast science and high-field physics. For example, the mid-infrared (8 μm) sub-cycle light fields can significantly improve the cutoff frequencies of high-order harmonic generation processes, and hence support the generation of shorter attosecond pulses.

传统的钛宝石超快激光逐渐与高次谐波产生、阿秒科学等前沿科学研究的应用需求不相适应。紧扣项目指南，本项目拟将当前局限于近红外波段（<3μm）的超快光场操控研究推进到中红外新波段（>5μm）。但是，长波中红外（5-8μm）超快激光面临着放大带宽、放大增益、色散操控等“三个受限”的技术挑战以及光参量放大中的热效应关键问题，需要开发适用于非氧化物晶体的光参量放大技术体系。对此，本项目拟采用温度/波长不敏感位相匹配新技术和“等脉宽传递”设计新思路，探寻一条可将近红外数周期脉冲“变换”为中红外（8μm）少周期脉冲的新途径，实现高重频（1kHz）、高峰功率(10GW)、极短脉宽（<3光周期）和CEP稳定等先进指标。基于申请人等发明的孤子脉冲压缩技术，本项目还将开展进一步的少周期和亚周期光场操控研究。本项目研究具有重要应用前景，有望大幅提升高次谐波产生过程的截止频率，从而支持更短的阿秒脉冲产生。

800nm波长的飞秒钛宝石激光是当前观测超快过程和探索强场现象的传统基石。随着超快科学特别是x波段高次谐波产生的深入研究，提出了如何产生前所未有的长波中红外（8-9μm）超快激光的挑战。本项目将超快非线性光学与光场操控进行创新结合，研制“波长十倍于钛宝石”的超快激光，并保持重复频率和峰值功率等其它技术指标与现有飞秒钛宝石再生放大器相当。本项目建立了长波中红外超快激光的“两步走”创新技术体系：2.3μm波长OPCPA + 9μm飞秒OPA；依托最新激光产品：钛宝石超快(10fs) + 碟片激光(1kHz高重频)；有特色地采纳国产新晶体BGSe优异的色散特性，实现了由2.3μm脉冲到9μm脉冲的“等脉宽传递”，并通过2.3μm放大光路上的色散器件AOPDF对9μm脉冲色散进行间接调控。本项目建立了国际国内少有的长波中红外（9μm）超快光场实验平台，整体技术性能达到或优于当前国际报道的最好水平：中心波长9μm（8-12μm可调谐）；重复频率1kHz；峰值功率1.6GW（现有平台具有可优化输出至10GW的能力）；脉冲宽度4个光周期（可进一步非线性压缩至<3光周期）；CEP稳定（通过2次差频过程实现对CEP的再提升）。本项目还发展了多项超快调控技术，包括温度与波长同时不敏感的超快位相匹配、中红外高效率准参量啁啾脉冲放大、基于级联非线性的超快群速度调控等。最后，本项目探索研究了中红外激光驱动下强场物理的新奇现象，展示了中红外激光在强场物理研究中的独特作用，为未来长波中红外激光平台的创新运用奠定基础。项目组共发表学术论文44篇（均标明资助号），授权美国专利2项、中国发明专利3项。人才培养方面，骨干成员何峰和马金贵分别获得基金委杰青（2019）和优青（2021）资助。中红外强激光团队获上海市激光学会五十周年激光科技奖（2020），中红外超快激光成果已经向高科技公司转化（2022）。