Air breakdown by pulsed-laser radiation in the 2.7- and 3.8-μm region

The breakdown thresholds of unfiltered laboratory air were measured in the 3.8- and 2.7-μm regions. The breakdown threshold at 10.6 μm was also measured under identical experimental conditions in order to provide a correlation with previous work. Measurements at different focal-spot radii were used to establish an empirical scaling law for the focal-spot radius dependence of the breakdown thresholds. This scaling law was then used to reduce all the data to a common focal-spot radius. The results indicate that the air breakdown threshold has a λ−2 dependence in the 2.7–10.6-μm range.