波长可调中红外飞秒频率梳的研究

Mid-IR frequency combs are attracting growing attention due to many potential applications, such as high-resolution molecular spectroscopy, high-accuracy absolute distance measurement, biomedicine and remote gas sensors. Our project aims at the development of high performance of 6.5-10 µm wavelength tunable mid-IR frequency combs. A stable and compact erbium-doped femtosecond fiber laser mode-locked by carbon nanotubes is chosen as seed source. The seed pulse is amplified in a chirped pulse amplification (CPA) system to act as femtosecond pump light. Part of the pump light is then shifted to the 1.85-2.05 µm region via Raman soliton self-frequency shift to form wavelength-tunable femtosecond signal light. The power of signal light is also increased by a CPA system with wide operating bandwidth. Finally, 6.5-10µm wavelength-tunable high power mid-IR frequency combs can be realized by the difference frequency generation between the pump light (1.55 µm) and the signal light (1.85-2.05 µm). Our research work can elucidate the generation mechanism of mid-IR frequency combs and significantly improve the output power of >6 µm mid-IR frequency combs needed for many applications.

中红外飞秒频率梳由于在精密分子光谱学、绝对距离测量、生物医学及大气传感等领域具有重要应用而吸引着科学家们的广泛关注。本项目以发展高性能6.5-10 µm波长可调中红外频率梳为动机，利用结构紧凑、稳定性高的碳纳米管锁模掺铒光纤激光器产生飞秒泵浦光种子源（1.55 µm），并在啁啾脉冲放大压缩系统中提高泵浦光脉冲功率；随后采用Raman孤子自频移方法将部分泵浦光波长频移到1.85-2.05 µm区域内形成波长可调的飞秒信号光，同时构建一个宽带工作的啁啾脉冲放大压缩系统以提高信号光功率；最终通过泵浦光与信号光的差频产生技术实现6.5-10 µm波长可调谐的高功率中红外频率梳。本项目的研究将深入阐明中红外频率梳的产生机理，突破当前6 µm以上中红外频率梳输出功率低下的瓶颈，为促进中红外频率梳的开发应用奠定基础。

中红外频率梳在精密分子光谱学、生物医学及大气传感等领域具有重要的潜在应用。本项目以发展高性能波长可调中红外频率梳为动机，利用结构紧凑、稳定性高的碳纳米管锁模掺铒光纤激光器产生97fs泵浦光种子源（1.55µm），并利用基于非线性光谱展宽及光栅对/空芯光子晶体光纤压缩的啁啾脉冲放大技术提高泵浦光功率，获得了最大平均功率超过1W，最大峰值功率高达240kW的泵浦光；随后在保偏光纤中采用Raman孤子自频移方法将部分泵浦光波长频移到1.85~2.05µm区域内形成波长可调的飞秒信号光，同时构建一个宽带工作的啁啾脉冲放大压缩系统以进一步扩大波长频移范围（最高可调谐至2.3µm）及提高信号光功率，在2µm波段输出功率最大可达1瓦左右，在放大过程中通过优化色散及增益光纤长度等可获得最大脉冲能量达13.3nJ，最短脉冲宽度95fs，最大峰值功率达104kW的信号光；最终泵浦光与信号光在中红外非线性晶体中（AgGaS2）采用差频产生技术实现了波长在6µm以上的可调谐中红外频率梳。本项目的研究阐明了中红外频率梳的差频产生机理及影响因素，为促进中红外频率梳的开发应用奠定基础。在该项目资助下，发表或者接受带有基金号标注的论文13篇，会议论文1篇，申请或授权专利2项，培养3名硕士生。