New Ytterbium based femtosecond lasers system are very interesting systems due to their high repetition rate / average power, compactness and long term stability due to direct diode pumping. Associated with nonlinear compression schemes (multipass cell or capillary), few cycle pulses are now available at around 1 µm. This presentation will present our recent work in this field and the extension of these sources in the mid-infrared by using intrapulse difference frequency generation and amplification to cover the 4 – 20 µm spectral range with high conversion efficiency. An optimization of the polarization state and chirp of the input pulses and a temporal synchronization leads to sub-two optical cycles CEP stable pulses at 8 µm with hundreds of mW average power (> µJ energy per pulses at 250 kHz).

The complicated electric field structure of ultrashort pulses as characterized by frequency-resolved optical gating (FROG) algorithms often results in local convergence, which does not accurately represent the actual field pulse. We present an efficient and universal test procedure applicable to any FROG retrieval algorithm that allows recognition of the erroneous local convergence. The 100% efficacy of the procedure is demonstrated using Line-Search FROG algorithm, and comparison is given with the performance of a standard extended ptychographic iterative FROG trace retrieval engine.

The generation of sub-five optical cycle pulses centered at 11.2 µm wavelength with 50 µJ energy at a 1 kHz repetition rate is reported. A GaSe optical parametric chirped pulse amplifier (OPCPA) is driven by the residual 2.0 µm pump and 5 µm idler of a high-energy midwave-IR OPCPA. The latter serves as driver for hard X-ray generation and this makes the achieved fs longwave-IR pulses available for X-ray pump-probe experiments.