高能量超快激光猝发脉冲光纤放大过程中时域畸变行为及控制方法

It is very difficult to generate high energy ultra-short laser pulse in fiber laser due to the limit of nonlinear effects, which occurs at high intensity. Therefore, how to avoid the nonlinear effects in the optical fiber has become an important topic in the field of optical fiber laser technology in order to realize high-energy ultra-short pulse output. Optical fiber amplification of burst pulses, on the other hand, provides an efficient way for solving this problem. However, the pulse distortion on the pulse and pulse envelope restrict further enhance of the total pulse energy. This project intends to develop a method by combining the theory and experiment to find the distortion characteristic and control methods for the burst pulses. We propose to include the time-dependent gain in theoretical calculation in solving the rate equation and nonlinear Schrodinger equation by taking into account of all the burst impulse transient process and steady state, and analyze the characteristics and the mechanism of double distortion; Experimentally, we will modulate the pump light of the signal amplifier, dynamically control internal gain of the fiber in order to control the burst pulse temporal morphology so that one can receive efficient burst pulse amplification without distortion. We expect that when this project is implemented, we should be to produce ultrafast fiber laser with burst pulse energy of more than 10 mJ or even 100 mJ per pulse. In addition, we should be able to produce desired burst envelopes based on needs of various applications. It will be of important scientific value and practical significance.

高脉冲能量输出成为超短脉冲光纤激光技术发展的短板。如何规避光纤中的非线性效应，实现高能量超短脉冲输出，成为光纤激光技术领域的一个重要课题。猝发脉冲光纤放大的方法提供了崭新的思路。但是，双重脉冲畸变行为成为制约整个包络脉冲能量进一步提升的瓶颈。本项目拟采用理论和实验相结合的方法，开展双重畸变特性分析和控制方法研究：在理论上补充增益时域调控因子，联合求解速率方程和非线性薛定谔方程，完成猝发脉冲瞬态过程和稳态过程的模拟，分析双重畸变特性的产生机理；进而在实验上，联合调制信号光与放大器泵浦光，实现光纤内部的增益动态调控，对猝发脉冲时域形貌进行控制，获得无畸变猝发脉冲的高效放大。该项目一旦获得实施，将在光纤激光器中突破十毫焦甚至百毫焦的超快激光脉冲能量，成为高能量超短脉冲光纤激光输出的突破口。还可以实现任意包络形貌的猝发脉冲输出，满足各种不同应用的需求。具有非常重要的科学价值和实际意义。

理论上模拟了连续信号光在光纤传输时，能量，反转粒子数和自发辐射沿光纤的变化。在此基础上，研究了猝发脉冲在光纤中的传播过程，猝发脉冲的时域形貌演变与脉冲宽度和峰值功率的关系，并且通过遗传优化算法对猝发脉冲进行了优化。实验中，通过设计全光纤猝发脉冲放大器光，验证了之前建立的抽运理论模型和模拟结果。为获得高功率的高能量猝发皮秒脉冲输出，首次提出了通过固体Q调制锁模振荡器和全光纤化Q调制锁模振荡器实现皮秒猝发脉冲输出并进行光纤放大的方案，开展了两种实验方案的研究：（1）基于被动Q调制锁模固体激光种子源进行单级光纤放大研究，实现平均功率85 W、猝发脉冲能量0.5 mJ、重频可调、串内子脉冲数量可控的皮秒激光输出。（2）开展基于全光纤Q调制锁模激光种子源的高功率猝发脉冲光纤放大器的研究，并在国际上首次实现平均功率166 W、脉冲能量8.3 mJ的无任何同步脉冲选择的猝发皮秒光纤放大输出。