| Abstract | The use of electron spin resonance for measurement of the ground state population (GSP) of Cr3+in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90°K and a mirror reflectance productR_{1}R_{2} > 0.08, the GSP at laser threshold was found to be 55 ± 5 percent in good agreement with theory and previous optical measurements. At room temperature, a limiting value of approximately 30 percent for the GSP was approached at high pump energies. Observations of the relativeR_{1}(3/2), R_{1}(1/2)thresholds at 90°K as a function of mirror reflectivity indicated that the2E excited state absorption cross section at the laser wavelength is less than5 \times 10^{-21}cm2. Detection of total internal reflection oscillations in cooled ruby lasers from ESR observations is also described. |
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