Novel ultrafast mid-infrared lasers for high harmonic generation in the soft X-ray region

Ultrafast soft X-ray (SXR) light is a powerful probe of material structure and dynamics on nanometer and femtosecond scales. It has a high penetration power, combined with elemental, chemical and magnetic specificity, while its high coherence enables 3D imaging with sub-10 nm spatial resolution.

In particular, coherent tabletop sources of extreme UV (EUV) based on high harmonic generation (HHG) have advanced sufficiently to drive a wide range of scientific and technological applications. However, until recently, demonstrating useful HHG-based SXR sources was challenging due to the lack of the robust mid-infrared drive lasers required to efficiently phase match the HHG upconversion process. Although HHG in the keV region was demonstrated in past work, the drive laser parameters (e.g. repetition rate, energy, pulse duration) were not sufficient to reach comparable levels as EUV HHG to support broad applications.

Here we present several approaches for demonstrating robust ultrafast mid-infrared wavelength lasers with parameters optimized for SXR HHG. Specifically, we have demonstrated a novel 1.5 μm and 3 μm optical parametric chirped pulse amplifier (OPCPA) system that generates SXR HHG to beyond the carbon K-edge at ~284 eV, as well a 3 μm OPCPA designed to reach the keV photon energy range at high flux. Finally, we will describe new approaches for ultrafast 2 μm lasers designed for high flux HHG up to >0.5 keV.