R 2 Line Optical Maser Action in Ruby

Abstract

Optical maser action at the R₂ line in ruby has been observed. Because of a fast thermal relaxation between the two ²E levels, it is not usually possible to satisfy the maser conditions at the R₂ line when stimulated emission is occurring at the R₁ line. However, if maser action can be suppressed at the R₁ line, even at high inversion, it can be made to occur at the R₂ line by the appropriate selection of operating conditions. This has been accomplished by using, for end reflectors, multilayer dielectric interference filters which have high transmission at the R₁ line and low transmission at the R₂ line. The selection of the operating conditions requires a correction of the absorption coefficients for the R₁ and R₂ lines based on the Boltzmann distribution between the two excited states. When the Boltzmann correction is made, the calculations show reasonable requirements on pumping threshold and reflectivities.