Absolute measurement of laser ionization yield in atmospheric pressure range gases over 14 decades
Daniel Woodbury, Robert Schwartz, Ela Rockafellow, Jared K. Wahlstrand, H M. Milchberg
Multiphoton and tunneling ionization are fundamental processes in strong field laser-matter interactions, and are integral to applications such as high harmonic generation, filamentation, and laser plasma production. However, measurements of ionization yields to date have limited gas samples to densities of <10^10 cm^-3, many orders of magnitude lower than in typical applications, which ignores potential contributions of higher density such as many- body interactions. Here, we measure femtosecond laser-driven ionization in atmospheric pressure-range nitrogen, argon, and air over an unprecedented 14 decades of absolute yield, using mid-IR picosecond avalanche multiplication of single electrons. Our results are consistent with theoretical rates for isolated atoms and molecules and quantify the ubiquitous presence of low level gas contaminants that can have wide ranging impact on laser-gas interactions, including the propagation of powerful infrared laser beams.