Tunable-diode-laser measurements of gain in optically pumped NH(3)

A tunable-diode laser is used for the first reported time to make gain measurements in a cw optically pumped 12-microm NH(3) amplifier. The tunability of the diode laser enables us to demonstrate that no inversion exists in the 12-microm laser and that Raman processes are responsible for the gain. High-sensitivity techniques allow gain coefficients as low as 0.001%/cm to be detected, and the experimental measurements are found to be in good agreement with theory.