Abstract
Measurements of the attenuation in a background gas, He or N2, of the uv radiation produced by a 1.7‐ns 4‐J CO2 laser irradiation of a copper target are reported. Photoionization cross sections of 0.4 Mb in He and 0.9 Mb in N2 are obtained. The photoionizing radiation is attributed to the 110.6‐Å M1 transition in copper.