Sub-two-cycle gigawatt-peak-power LWIR OPA for ultrafast nonlinear spectroscopy of condensed state materials.

The application of high-power, few-cycle, long-wave infrared (LWIR, 8-20 µm) pulses in strong-field physics is largely unexplored due to the lack of suitable sources. However, the generation of intense pulses with >6 µm wavelength range is becoming increasingly feasible with the recent advances in high-power ultrashort lasers in the middle-infrared range that can serve as a pump for optical parametric amplifiers (OPA). Here we experimentally demonstrate the feasibility of this approach by building an OPA pumped at 2.4 µm that generates 93 µJ pulses at 9.5 µm, 1 kHz repetition rate with sub-two-cycle pulse duration, 1.6 GW peak power, and excellent beam quality. The results open a wide range of applications in attosecond physics (especially for studies of condensed phase samples), remote sensing, and biophotonics.

Multipass spectral broadening of 18 mJ pulses compressible from 1.3 ps to 41 fs.

Nonlinear compression of laser pulses with tens of millijoule energy in a gas-filled multipass cell is a promising approach to realize a new generation of high average power femtosecond sources. For the first time, to the best of our knowledge, we demonstrate nonlinear broadening of pulses with about 18 mJ of energy at a 5 kHz repetition rate in an argon-filled Herriott cell and show compressibility from 1.3 ps to 41 fs. In addition to the large compression factor, the output beam has an outstanding quality and excellent spectral homogeneity. Furthermore, we discuss prospects to scale the energy to the 100 mJ level in the near future.

On-target temporal characterization of optical pulses at relativistic intensity.

High-field experiments are very sensitive to the exact value of the peak intensity of an optical pulse due to the nonlinearity of the underlying processes. Therefore, precise knowledge of the pulse intensity, which is mainly limited by the accuracy of the temporal characterization, is a key prerequisite for the correct interpretation of experimental data. While the detection of energy and spatial profile is well established, the unambiguous temporal characterization of intense optical pulses, another important parameter required for intensity evaluation, remains a challenge, especially at relativistic intensities and a few-cycle pulse duration. Here, we report on the progress in the temporal characterization of intense laser pulses and present the relativistic surface second harmonic generation dispersion scan (RSSHG-D-scan)-a new approach allowing direct on-target temporal characterization of high-energy, few-cycle optical pulses at relativistic intensity.