高能量掺镱飞秒激光多薄片非线性压缩的数值模拟

Numerical Simulation of Nonlinear Pulse Compression of High-energy Ytterbium-doped Femtosecond Laser Based on Multiple Thin Solid Plates

对高能量掺镱激光器进行腔外压缩,是获得高能量少数周期脉冲的重要方式。通过数值模拟研究了单脉冲能量为250 mJ,波长为1 030 nm的高能量掺镱激光器通过固体多薄片介质进行非线性脉冲压缩的过程,及介质周期、厚度对频谱展宽的影响。在优化频谱展宽条件的过程中发现,不超过介质损伤阈值的情况下,固体薄片组的周期和厚度对频谱展宽具有正向影响。通过选取合适的介质厚度及周期,激光频谱通过熔融石英介质进行展宽,最终输出的光谱带宽达229 nm,补偿色散后,激光脉冲由500 fs压缩至16.2 fs,压缩比达到30。研究结果为实现高能量激光脉冲的非线性压缩提供了理论参考。

High-energy and ultrafast laser has been an ideal source for frontier physical issues, such as high harmonic generation, attosecond pulse generation, extreme ultraviolet optical frequency comb and electron acceleration. Due to the wide gain bandwidth, titanium-doped sapphire lasers can directly emit laser pulses of few periods. While due to the limitation of quantum efficiency, pumping power and thermal effect, the energy of laser pulse is limited. On the other hand, external pulse compression is also used to generate fewcycle laser pulse, by means of gas-filled multi-pass cell, gas-filled hollow-core fiber, and multiple solid plates. Laser pulse compression based on multiple thin solid plates is characterized by stable performance, high repeatability, and high cost performance. The nonlinear refractive index coefficient of solid medium is higher than that of gas medium. It is easier to generate nonlinear process in solid medium. The spectrum becomes much wider than the original spectrum, as a result of self-phase modulation effect. With efficient dispersion management and appropriate input laser beam size, high-energy laser pulses can be compressed through multiple thin solid plates. Research based on multiple thin solid plates aims mainly at titaniumdoped sapphire laser, with shorter laser pulse(<100 fs) and lower energy(<10 mJ). For laser pulses with higher energy, a large-size beam is adopted to control the energy fluence on solid medium. High quantum efficiency and excellent thermal conductivity make the medium of ytterbium to generate high energy and high average power laser pulse. And the ytterbium doped laser is more compact and integrated than titanium-doped sapphire laser. The external pulse compression of high-energy ytterbium doped laser is a reliable scheme to generate high-energy and ultrashort pulses. Previous research about pulse compression of ytterbium doped laser by multiple thin solid plates is also based on low energy laser. In this paper, we demonstrate numerically the nonlinear pulse compression of the high-energy ytterbium doped laser, with an energy of 250 mJ and a wavelength of 1 030 nm, based on multiple thin solid plates. The influence of period and thickness of solid plates is also studied. The period and thickness of solid plates have a positive effect on the spectral broadening when the laser energy fluence is lower than the damage threshold of solid medium. By using appropriate solid plates, a femtosecond supercontinuum is generated with a bandwidth of 229 nm. And the pulse is compressed from 500 fs to 16.2 fs, with a high compression ratio of 30. Besides, we design a three stage pulse compressor to generate laser pulse with different pulse widths to meet the requirements of different applications, such as 51.3 fs, 26.6 fs, 16.2 fs. The simulation results are feasible for high-energy laser pulse compression.