ENERGY-STORAGE AND HEAT DEPOSITION IN FLASHLAMP-PUMPED SENSITIZED ERBIUM GLASS LASERS

Measurements of population inversion energy storage and heat deposition in flashlamp-pumped Nd:Yb:Er:glass, and Cr:Nd:Yb:Er:glass lasers are reported. A thermal camera is used to measure temperature changes following isolated flashlamp pulses. A rate equations model is developed in order to determine energy storage from the output versus input energy characteristics of erbium lasers operating in a free-oscillation mode. Contributions of different sensitizers are distinguished by spectrally filtering flashlamp-pump radiation. It is determined that in Nd:Yb:Er:glass, ytterbium-sensitized pumping contributes 85% to the total erbium inverted population energy storage. Long flashlamp pulse durations are therefore required for efficient Nd:Yb:Er:glass laser operation. Direct erbium, and neodymium-sensitized pumping is determined to be relatively inefficient, although the corresponding visible part of the pump spectrum contributes in Nd:Yb:Er:glass as much as 65% of the total deposited heat. Chromium codoping is observed to significantly increase energy conversion efficiency of pumping in the visible, allowing shorter flashlamp pulse durations in Cr:Nd:Yb:Er:glass lasers. Ratios of the deposited heat per unit stored energy in both glasses are compared for several spectral regions.