Experimental and theoretical investigations for describing pressure dependence of amplified spontaneous emission output energy, small signal gain and electrical conductivity in nitrogen lasers

An experimental arrangement consists of an oscillator amplifier (OSC-AMP) N2 laser system having electrodes of different lengths, lAMP, was used to measure the amplified spontaneous emission (ASE) output energy extracted from the AMP section at different gas pressure, pAMP, and also the AMP small signal gain, g0 at a constant pAMP. It was observed that the extracted ASE output energy with respect to operational gas pressure has a non-symmetrical character. For explaining the observed behavior two different models for numerical calculations were applied for the results to be compared with each other and also with the experimental observations. The first model, i.e. the model of geometrically dependent gain coefficient (GDGC) was found to explain the pressure dependencies the observed behaviors of threshold and saturation lengths. The second model, which is based on using rate equations for N2 lasers, coupled to the circuit electric discharge was used to calculate the pressure dependences of the ASE output energy and small signal gain. The results showed that ASE output energy versus gas pressure had a symmetrical behavior and within a limited range of gas pressure, small signal gain is a constant value. As geometrically the small signal gain and the electrical conductivity behave similarly, the model was also applied for predicting the pressure dependence of the electrical conductivity. Calculations of g0 vs. lAMP at pAMP = 90 Torr based on applying both models are comparable with the measurements. It is concluded that the GDGC model can be suitably used for predictions of small signal gain, threshold and saturation lengths provided that ASE experimental measurements are available. The modified rate equations, on the other hand, can give appropriate results in absence of experimental measurements.