Study Of Optically Pumped Gas THz Laser Energy Conversion Efficiency

Terahertz wave is between the microwave and infrared wave in the electromagnetic spectrum, which belongs to the sub-millimeter wave. As its nature is very unique, it can penetrate metal, non-polar materials, smoke and dust without harm,and it is significant to study the high energy conversion efficiency of the THz source.This paper starts with increasing the energy conversion efficiency of the optically pumped terahertz laser, using TEA CO2 laser as the pumping source, using ammonia gas as working medium to study the two main factors(pumping energy and gas pressure) of energy conversion efficiency theoretically and experimentally.Theoretically, the three-level rate equations were built, using the fourth order Runge-Kutta method and MATLAB program to numerically simulate the rate equations, and the influence of pumping energy and gas pressure on the energy levels and THz photons was analyzed from the angle of laser generation mechanism. Under a specific pressure, the energy conversion efficiency changing with pumping energy was studied, and the maximum value was 0.3%, it remained from 200 m J to 1J, and during0~200m J and 1~50J, the energy conversion efficiency was lower than 0.3%. Under a specific pumping energy, the energy conversion efficiency changing with pressure was studied, and the best working pressure was 550 Pa, what’s more, the influence of pumping laser absorption process in NH3 gas on the gas pressure and the energy conversion efficiency was considered.Experimentally, a super-radiant optically pumped terahertz ammonia gas laser was designed and built, the performance of TEA CO2 laser(the pumping source) was test; the absorption properties in NH3 gas of TEA CO2 laser’s 9R(14), 9R(16) and 9R(18) lines were studied. Under a specific pressure, the energy conversion efficiency changing with pumping energy was studied, a conclusion was obtained that the energy conversion efficiency changing with pumping energy showed a linear growth law, and when the pumping energy was 200 m J, the maximum energy conversion efficiency was0.4%; Under a specific pumping energy, the energy conversion efficiency changing with pressure was studied, a conclusion was obtained that the pressure at the maximum energy conversion efficiency was 550 Pa. Comparing the theoretical and experimental energy conversion efficiency, the cause of the error was analyzed, and the advantagesand disadvantages of the theoretical model was pointed out, and finally the direction of the follow-up study was given.