Single-ended infrared photothermal radiometric measurement of quantum efficiency and metastable lifetime in solid-state laser materials: The case of ruby (Cr3+:Al2O3)

A simple, self-consistent frequency-scanned photothermal radiometric (PTR) detection scheme was applied to the measurement of the metastable state de-excitation parameters of a ruby laser rod. The radiative quantum efficiency and lifetime in this material were calculated from the extrema of the photothermal phase and the amplitude slope versus the excitation laser beam modulation frequency curves, without recourse to the conventional second measurement to eliminate effects of photothermal saturation. This technique simplifies significantly the experimental methodology, guarantees uniqueness of the measured quantities, and increases the measurement range of lifetimes as compared to other photothermal-based methods. Therefore, it may prove valuable for fast industrial quality control, as well as for fundamental studies of laser materials