Femtosecond coherent spectroscopy at 800 nm: measuring high-field ionization rates in gases with MI-FROG

摘要

Previous studies of ultrafast ionization have relied on spectral power density measurements using 100-ps pulses. As the detailed structure of the ionization-front blue-shifted spectra depends on a complicated interplay of the input pulse structure (i.e., its phase) and the ionisation dynamics, the conclusions made from these experiments have been at best well thought out and limited inferences. To surpass these limitations and achieve a quantitative measure of the ionization rate independent of probe structure, we have utilized an experiment configuration which, by utilizing three power-spectra channels and one optically gated frequency-resolved channel per each of four CCD images (pumped and unpumped cases with one or two probe pulses), provides simultaneous and self-consistent dual-channel power spectra and frequency domain interferograms, MI-FROG6 and FROG7 data.