We consider ruby as a linear, uniaxial, maxwellian medium, which, in its absorbing state, has axially dependent material constants. It is made active by pumping with electric fields, in the region of shorter-wavelength absorption bands, which, by means of an energy transfer, induce source-type electric fields having constant amplitudes in the <i>R</i><sub>1</sub> and <i>R</i><sub>2</sub> regions, and make possible absorption, spontaneous emission, and stimulated emission. Experiments indicate that the absorption, fluorescence, and laser action are all maximum for electric fields perpendicular to the optic axis, and minimum when the electric field is parallel to the optic axis; the relative irradiances and shapes of the <i>R</i><sub>1</sub> and <i>R</i><sub>2</sub> bands in all cases depend upon the orientation of the plane of polarization of the emerging radiant flux relative to the optic axis. Attempts are made to compute the spectral distributions in the <i>R</i><sub>1</sub> and <i>R</i><sub>2</sub> bands for the ordinary and extraordinary waves, neglecting all boundary-value problems. Agreement was found to be possible only in the region below the threshold of laser action.
A. I. MAHAN, C. BITTERLI, S. M. CANNON, and D. G. GRANT, "Ruby as a Macroscopic Fluorescing and Laser Material," J. Opt. Soc. Am. 59, 49-59 (1969)