高亮度任意波形脉冲激光理论与关键技术研究

Precise control of laser characteristics in time domain is of increasingly demanding, especially in areas such as laser micro-nano machining, laser radar and the National Ignition Facility (NIF). Parameters such as the pulse repetition rate (PRF), pulse duration, pulse amplitude are required to be adjusted as the users like. Besides, pulsed laser with desired pulse shapes, such as flat-top waveform and chair-like pulse shape, is of significance. Moreover, laser sources with both high brightness and arbitrary waveforms is in great demand to explore the interaction between laser and matter. As to the traditional Q-switched lasers, the pulse shape is Gaussian-like and could not be adjusted conveniently. This project proposes a solution to realize the arbitrary waveform output for a solid-sate MOPA laser. The MOPA laser is seeded by a semiconductor laser, which could be easily modulated to change the parameters in time domain. Two cascade fiber amplifiers are employed to boost the small signal from the semiconductor laser, taking advantage of high gain of the fiber amplifier. Finally, the output power is scaling up through three Nd:YVO4 amplifiers, with good beam quality. By solving the inverse problem of amplifiers, the input pulse shape and average power of the MOPA system are obtained. Arbitrary waveforms are then realized for the MOPA system, as well as adjusted PRF and pulse duration and good beam quality resulting from combined guidance effect. Finally, the process of nonlinear-coupling is studied to realize the second harmonic generation with arbitrary pulse shapes. This project will detail investigate the pulse distortion in laser amplifiers and break through the technical bottleneck in pulse shape control, solution of inverse problem, generation of arbitrary waveforms and efficient amplification of small signal. It is of very important theoretical research sense and practical application value to study and control the pulse parameters in laser amplifiers.

激光精密微纳加工、激光雷达、国家点火装置等领域对激光的时域特性要求越来越苛刻，不仅仅希望重复频率、脉宽参数、幅值可调，也提出平顶脉冲、“h”形脉冲等需求，甚至需要实现任意波形脉冲激光输出。传统的调Q激光器，脉冲波形呈高斯形状，难于调节。本项目提出了半导体/光纤/固体三模混合种子放大方案，充分发挥了半导体激光器易于调制的优点，光纤放大器超强的小信号放大能力以及固体放大器的功率提取能力。提出了通过求解放大器逆向问题的输入波形及功率参数，利用本项目组提出的激光放大复合导引效应，在实现激光重频和脉宽独立可调节的同时，获得任意波形(超快激光包络)的高亮度输出。最后还将研究任意波形脉冲激光的非线性耦合过程，实现任意波形的倍频激光输出。本项目将突破激光放大过程中波形控制、逆向问题求解、微弱信号高效放大、任意波形产生、突发模式脉冲串等关键技术，对于脉冲激光时域特征研究具有重要的理论意义和实际应用价值。

激光精密微纳加工、激光雷达、国家点火装置等领域对激光的时域特性要求越来越苛刻，不仅仅希望重复频率、脉宽参数、幅值可调，也提出平顶脉冲、“h”形脉冲等需求 ，甚至需要实现任意波形脉冲激光输出。传统的调Q激光器，脉冲波形呈高斯形状，难于调节。本项目提出了半导体/光纤/固体三模混合种子放大方案，充分发挥了半导体激光器易于调制的优点，光纤放大器超强的小信号放大能力以及固体放大器的功率提取能力。建立了放大器小信号增益的三维模型，数值分析了各个因素对小信号增益的影响，实验上开展了半导体/光纤/固体混合放大MOPA激光实验。实现了重频及脉宽大范围独立可调的高峰值功率、高功率的近基模脉冲激光输出；研究了放大器中实现任意波形输出的实验及理论方法，指出放大器波形预补偿问题的关键在于放大器的初始增益；利用可编程种子源，补偿了多级放大器的脉冲畸变，成功得到了多种常用波形；将此理论方法应用到产生目标包络形状的突发模式激光中，产生了内突发重频为40 MHz，外突发重频为100 kHz和40 kHz的脉冲串输出；提出了利用弱反馈实现亚纳秒窄脉冲方法，理论分析了无腔及弱反馈结构下脉冲固体激光的输出特性，实验测得弱反馈条件下的脉冲宽度为550 ps，仅为1.50倍的往返渡越时间，验证了无腔及弱反馈实现亚纳秒窄脉冲输出特性理论的正确性；还探索了亚纳秒MOPA系统在突发模式激光输出特性，内突发重频达到80 kHz时仍保持脉冲宽度小于500 ps，实验中还观察、统计与分析了高增益条件下的谐振腔光学怪波现象，指出了横模拍频在触发光学怪波中的作用。本项目突破了激光放大过程中波形控制、逆向问题求解、微弱信号高效放大、任意波形产生、突发模式脉冲串等关键技术，对于脉冲激光时域特征研究具有重要的理论意义和实际应用价值。