Ultrafast lasers have seen significant increase in average power over the past decade, thanks to the use of Ytterbium-ion-doped gain materials in geometries (fibers, slabs, thin-disks) that are advantageous for heat extraction. The Yb:YAG thin-disk technology has been particularly remarkable in developing high-average power ultrafast lasers with average power exceeding 1 kW and pulse energy up to 1 J. Due to the limited gain bandwidth in conjunction with spectral gain narrowing, Yb:YAG thin-disk lasers can only support pulses of ~1 ps, which may not be short enough for some applications. This limitation has stimulated a wave of research during last five years on nonlinear post-compression of the high-average power ps-pulses.

In this talk I will discuss our progress made on the development of high-average power ultrafast laser technologies at LLE. I will start with a brief review of the Yb:YAG thin-disk technology before describing briefly the development of a high-average power Yb:YAG thin-disk regen and the demonstration of energy-scaling of nonlinear post-compression using divided-pulse nonlinear compression. I will then discuss in detail our very recent progress on demonstrating a nonlinearity-tunable regenerative amplifier for high-average power ultrashort pulse generation, a technique that is fundamentally different from the chirped-pulse amplification. This technique is particularly suitable for developing compact and cost-effective high-average power ultrafast lasers.