Effect of sensitizers on flashlamp-pumping efficiency and heat deposition in Er glasses

Abstract

Measurements of energy storage and heat deposition in flash-lamp pumped Nd:Yb:Er: glass, and Cr:Nd:Yb:Er: glass lasers are reported. Energy storage is determined indirectly by measuring output vs. input energy characteristics of erbium lasers operating in a free oscillation mode. A thermal camera is used to measure temperature increase following isolated flash-lamp pulses. Contributions of different sensitizers are distinguished by spectrally filtering flash-lamp 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 flash-lamp pulse durations are therefore required for efficient Nd:Yb:Er: glass laser operation. Direct erbium, and neodimium 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 co-doping 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. In addition, analysis shows the ratio of the total heat generated per unit stored energy to be in Cr:Nd:Yb:Er: glass lower than in Nd:Yb:Er: glass.