Abstract
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.