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

An experiment configuration that provides simultaneous and self-consistent dual-channel power spectra and frequency domain interferograms, MI-FROG and FROG data was used in this study to obtain a quantitative measure of the ionization rate independent of probe structure. Data was taken with 600 and 1000 Torr of He, Ne, Ar, Kr, N₂ Air, and Xe at pump-probe increments of 12 fs. The polarization of the 124-fs, 400-nm pump was oriented either parallel or orthogonal to that of the weak 800-nm, 175-fs, multipulse probe. The 600 Torr data utilized the same pump intensity among all gases, while for the 100 Torr data the pump intensity was set just above and below the visual appearance of a breakdown spark. In general, significant results were obtained.