Calculated-experimental evaluation of the gain/absorption spectra of several optically pumped NH3systems

Three NH
3
optically pumped laser systems were chosen for study wherein one pair of energy levels was the ground state
ga \leftrightarrow gs
transition in the 18-26 GHz range, where tunable microwave sources are available for gain/absorption probes. The objective was to experimentally evaluate the validity and accuracy of a density matrix calculation, using typical approximations, in providing a complete description for double and triple resonant (first, third, and fifth order) gain/ absorption spectra. It was demonstrated that gain/absorption peak frequencies could be calculated to better than 10 MHz, absolute gain/absorptions to within a factor of 2 to 3, and
M
-split linewidths for counterpropagating pumps to ±2 MHz. At pump intensities above 100 kW/cm
²
, most of the
M
-split gain/absorption peaks could be well resolved.