锁模建立过程中飞秒光纤激光器的瞬态时-频特性

Femtosecond fiber lasers suffer from nonlinear noise, challenging to control the pulse shapes, and low conversion efficiency. There are rich laser dynamics during the build-up of mode locking in these lasers. It is of great importance to investigate such processes, which can unveil the origin of nonlinear noise, individual shaping mechanisms of different nonlinear pulses, and strong dissipative effects that decreases the conversion efficiency. However, since the build-up of mode locking is so fast that traditional measurement methods cannot response to this process. This project combining spatio-temporal and dispersive Fourier transformation technologies, can measure the transient process and will address several scientific problems. In particular, we will unveil the strong dissipative effect during the build-up of mode locking, leading to high conversion efficiency; investigate the shaping mechanisms accounting for different nonlinear pulses, contributing to pulse shape control; reveal the origin of multiple pulsing; provide a method for real-time measurement of coherence; uncover the competition between decoherence and coherence processes. This project has scientific significance in the field of femtosecond lasers in terms of noise suppression, waveform control and conversion efficiency increasing.

飞秒光纤激光器存在非线性噪声，波形难以操控，转换效率低的问题。锁模从启动到稳定的瞬时过程中，飞秒光纤激光器暗含丰富的动力学特性。研究这一过程具有重要意义，可从根本上揭示非线性噪声的来源，不同波形的整形机制，影响转换效率的强耗散机制。然而由于该过程变化太快，传统的探测方法无法响应这一过程。本项目结合空-时法及色散傅里叶变换法，实现对这一瞬态过程的实时测量，研究若干重要科学问题。将揭示锁模启动过程中，激光器内的能量强耗散机制，提高转换效率；研究不同非线性脉冲的整形机制，有利于波形操控；研究启动过程中，多脉冲的产生过程；提出相干性实时探测方法，揭示锁模启动过程中，退相干与相干机制的竞争过程。本项目的研究对飞秒光纤激光器噪声抑制，波形操控，转换效率的提升具有重要科学意义。

飞秒光纤激光器存在非线性噪声，波形难以操控，转换效率低的问题。锁模从启动到稳定的瞬时过程中，飞秒光纤激光器暗含丰富的动力学特性。研究这一过程具有重要意义，可从根本上揭示非线性噪声的来源，不同波形的整形机制，影响转换效率的强耗散机制。然而由于该过程变化太快，传统的探测方法无法响应这一过程。本项目结合空-时法及色散傅里叶变换法，实现了对这一瞬态过程的实时测量，研究了若干重要科学问题。揭示了锁模启动过程中，激光器内的能量强耗散机制，研究发现这是能量过冲效应导致的；结合理论和实验揭示了锁模建立过程一共包含六个非线性过程，依次是调制不稳定性，锁模，自相位调制不稳定性，脉冲分裂，脉冲相互作用和脉冲湮灭。理论模拟也再现了整个建立过程。这一发现表明实际激光器中由于存在色散，非线性，增益竞争，驰豫振荡等效应，锁模建立过程会比噪声涨落假设复杂。本项目的研究对飞秒光纤激光器噪声抑制，波形操控，转换效率的提升具有重要科学意义。