基于弱CW光调控的长脉冲泵浦中红外超连续谱研究

Mid-infrared supercontinuum (SC) lies in the atmospheric transmission window and eye-safe range, and the characteristics of broad spectral range, high power density and high spectral flatness, make it has potentially wide applications in industry, medicine, and national defense fields. Affected by modulation instability originated from random noise, the mid-infrared SC pumped by long laser pulse, such as picosecond (ps), nanosecond (ns), continuous wave (CW), suffer from poor coherence, stability, and signal-to-noise ratio (SNR), and the degradation of the SC property greatly limits the applications of mid-infrared SC. This project will carry out a detailed research of mid-infrared SC generation pumped by longer pulses with a weak CW for the first time. The modulation instability can be suppressed by the injected weak CW, and the four-wave mixing effect can be enhanced, and the resulting SC coherence, stability, SNR and spectral width can be greatly improved. We also carry out a detailed research on the related optical rogue waves (ORW) in SC generation in ZBLAN fiber pumped by long laser pulse. The ORW characteristics, formation mechanism, and effects of the weak CW-triggering will be explored. This research project is expected to realize a mid-infrared SC source with high coherence, stability and SNR generation in fiber pumped by longer pulses, and it can also provide some valuable suggestions for researches in ultraviolet and far-infrared SC.

中红外超连续谱具光谱范围宽、功率密度高、平坦性好等特点，且处于大气传输窗口和人眼安全区，在工业、医疗、国防等领域有广阔的应用前景。受到源于随机噪声的调制不稳定影响，目前长脉冲 (ps、ns、CW) 泵浦中红外超连续谱的相干性、稳定性、信噪比等较差，大大限制其应用范围和价值。为解决上述问题，本项目首次开展基于弱CW光调控的长脉冲泵浦中红外超连续谱研究，通过注入弱CW光来抑制调制不稳定作用，增强四波混频效应，显著提高超连续谱相干性、稳定性、信噪比和谱宽度。同时首次对长脉冲泵浦ZBLAN光纤产生的超连续谱中光畸波开展研究，探究光谱中光畸波特性、形成机理，以及弱CW光调控后光畸波的变化规律。本项目研究有望实现在长脉冲泵浦的光纤中获得高相干性、稳定性和信噪比的中红外波段超连续谱光源，同时为紫外、远红外等其它波段的超连续谱研究提供借鉴作用。

超宽光谱SC涵盖大气透射窗口和人眼安全波段，在众多领域具有重要的应用价值。对于长脉冲激光泵浦非线性光纤产生的SC来说，在源于噪声MI作用下，产生的新频谱的相位是随机分布。尽管形成的SC具有较好平坦性，但新频率光谱相干性产生严重的劣化，这大大限制SC光源在高精密光学频率测量、光通信、脉冲压缩等方面的应用，如何提高和改善SC相干性已经变成一个亟需解决的问题。.飞秒激光脉冲具有极短作用时间和极高的峰值功率，其可广泛应用于工业、科研、医疗等领域。近年来基于NALM锁模机制重新引起了研究人员的兴趣，并对如何提高锁模的自启动能力研究取得一定进展，但受到谐振腔结构、增益光纤和关键器件等因素的影响，如何获得高重频、高稳定性和低噪声的飞秒脉冲仍然需要开展深入研究。.本文通过外注入弱CW光来调控ps脉冲泵浦SC输出特性，同时研究高非线性环境下新型锁模激光器输出特性，获得的主要结论为：.1.注入100 Hz线宽弱CW调控ps脉冲泵浦SC输出，实验上观察到2 μm波段的拉曼孤子，提高SC输出的光谱宽度、相干性和信噪比。.2.通过增加腔内的非线性效应，获得脉宽从8.21 ns -128.23 ns可调谐方波NLPs输出；观察到方波型NLPs向高斯型NLPs裂化过程及多态振荡现象，即单孤子簇、高阶谐波锁模和局域随机多脉冲。.3.在方波NLP中实现多样式次脉冲输出，获得2994阶次谐波次脉冲输出, “L”型强度分布表明光畸波在次脉冲输出的存在。.4.在9字腔锁模光纤激光器中实现暗方波NLPs输出，观察到暗方波NLPs在腔内时域和频域演变过程。.5.实验观察到了准相干的类噪声锁模脉冲，研究其输出特性及相邻脉冲之间一阶相干度。.6.通过将孤子分子注入到一个插入一段高非线性光纤的光纤环镜中，实现双向输出的超连续谱光频梳，并通过调控孤子分子特性来调节SC光梳的梳齿结构。