Large gain of gaseous ammonia near 1 THz

Large gain of optically pumped gas (ammonia) was obtained at 1.073 and 1.068 THz. Tunable quantum cascade laser allows to excite sharp mid-infrared transitions of ammonia close to 967 cm
^-1
. Obtained population inversion of umbrella modes near 1 THz is not accessible by any other pumping methods. Exceptionally high gain demonstrated can be used for future terahertz applications. The proposed method of measurement has high potential for evaluation of gain for different gases optically pumped by quantum cascade lasers.