Lasing of molecular HBr in the four-micron region pumped by a DF-laser

High efficiency optical pumping of 4-μm HBr-laser was performed by the principal 2P9 line (3.836 μm) of pulsed DF-laser. Precise coincidence revealed of this laser transition with R2 line of the fundamental absorption band of the heavy isotopomer of hydrogen bromide was utilized. Lasing within 0.3-15 Torr pressure range was observed in overall (4.017-4.215) μm spectral range, at both off-axis and the collinear pumping geometry (pump fluence of 0.2 - 0.4 J/cm 2 , pulse FWHM duration ~300 ns). Complex behaviour of HBr-laser emission peak intensity, pulse duration and time delay upon the gas pressure was analyzed. Energy conversion efficiency at P=10 Torr was increased from ~2% to more than 5%, when collinear scheme with better mode-matching was utlized. It is believed that the efficiency may be additionally improved by optimization of HBr-laser cavity losses.