Optical EngineeringQuantum efficiency and metastable lifetime measurements in solid state laser materials via lock-in rate-window photothermal radiometry: technique and application to ruby (Cr3+:Al2O3)
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The newly developed photothermal detection technique of rate-window infrared radiometry is applied to the measurement of the metastable state deexcitation parameters of a ruby laser rod. The technique employs a square laser pulse and monitors the infrared photothermal radiometric response of the sample. By applying the photothermal lock-in rate-window concept, the radiative lifetime and quantum efficiency of Cr3+:Al2O3 are measured with optimal SNR and simple, unambiguous interpretation from the extremum in the lock-in analyzer in-phase rate-window signal. This technique simplifies significantly the experimental methodology; optimizes the photothermal SNR, which is inherently low in conventional frequency or time-domain photothermal measurements; and offers extended measurement dynamic range for both radiative quantum efficiency and lifetime in laser materials, as compared to frequency-scanned harmonic detection. Therefore, rate-window infrared photothermal radiometry may prove a valuable tool for the combined measurement of metastable lifetime and nonradiative energy conversion efficiency in laser materials with fast deexcitation rates.