Shuji Ogawa

Role of N2 gas in a transverse-flow CW CO2 laser excited by silent discharge

Experimental and theoretical investigations have been carried out on the effect of N2 gas in a transverse-flow CO2 laser excited by silent discharge (SD). It has been found that the addition of N2 is a cause of the increase of excitation efficiency compensating the effect of the increase in reduced electric field strength E/N. The excitation efficiency expressed as a function of N2 gas concentration agrees qualitatively with the results of a Boltzmann equation analysis in which the electric field is assumed to be temporally stationary and spatially uniform. The decrease in gain coefficient with N2 concentration is explained well by a model in which the stream of excited molecules due to transverse flow of gas is taken into account. The optimum gas composition for SD excitation is found to be a mixture of CO2-CO-N2-He=8-4-60-28. The optimum molar fraction of N2 is extremely high in comparison to those values reported for other types of discharge excitation.