Measurement of the reflectivity of metal mirrors acted on by laser radiation

A study was made of the reflectivity of copper, aluminum, and stainless steel mirrors acted on by neodymium-laser pulses of ~400 nsec duration and ~70 J energy. The temperature and luminosity of the irradiated surface were recorded at the same time. Within an experimental error of ±10%, the reflection coefficient of the mirrors remained constant right up to the energy density at which intense evaporation of the metal occurred. There was a substantial reduction in the reflection coefficient when an absorbing discharge formed in the vapor. The results obtained were compared with heating calculations using the linear theory of heat conduction and data from other publications.