Reflection of pulsed ruby laser radiation by a copper target in air and in vacuum

Measurements of the reflection coefficient of a target–plasma system and of the optical thickness of the plasma were used to find the reflection coefficient of a target surface screened by a plasma and subjected to laser radiation with peak power density 230 MW/cm². The target reflection coefficient in vacuum remained constant during a laser pulse and it was equal to the value obtained below the plasma formation threshold. In air the reflection coefficient fell to 0.23 because of the formation of a geometrically thin absorbing plasma layer on the target surface. This major difference between the behavior of the reflection coefficient of the target surface in vacuum and in air was responsible for the difference between the thermal coupling coefficients in these two cases.