The power of femtosecond lasers based on Ti: sapphire or Yb-doped gain media has reached a high level by using chirped pulse amplification. The dispersive elements are normally employed in CPA devices, thereby increasing the complexity and cost of the laser system. However, for the Nd-doped laser, its power can be amplified to hundreds of microjoules or even several millijoules directly without CPA technology. So compressing the picosecond pulse to obtain femtosecond laser pulses with hundreds of microjoules pulse energy by post-compression technology becomes meaningful. The pulsed post-compression technology is the combination of nonlinear spectral broadening and dispersion compensation. Currently, the most effective method of nonlinear spectral broadening is achieved through self-phase modulation. The multi-pass cell (MPC) device based on self-phase modulation for broadening spectral bandwidth has been extensively studied, since it was demonstrated. The MPC concept demonstrates significant practical benefits. Essentially, it requires only two curved mirrors and a Kerr medium in between, making it a cost-effective and easily implementable method. Moreover, the MPCs are robust, quite insensitive to beam pointing, and can evendeal with small mode mismatch without transmission losses. These favorable characteristics make MPCs very attractive not only for scientific applications, but also for commercial and facility laser systems where reliability is crucial. The striking progress of the technique in the past six years has made it possible to obtain high average power femtosecond laser.

In this work, we demonstrate the generation of a high average power femtosecond laser pulse by nonlinearly compressing the picosecond pulse in the Herriott multi-pass cell device, and the distribution of eigenmode is analyzed. With this efficient and robust scheme, the spectrum is broadened from 0.20 nm to 2.75 nm, with a broadening ratio of 13.75, and the pulse duration of a picosecond amplifier is compressed from 1.25 ps to 780 fs, with a compression factor of 16. The average power before and after pulse compression are 100 W and 71.3 W respectively, so the overall transmission reaches 71.3%. The present scheme offers a viable route to low-cost and simple-configuration high-power femtosecond lasers driven by Nd-doped picosecond amplifiers.