Amplified spontaneous emission in N2 lasers: Saturation and bandwidth study

A complete ASE analysis in a 3-level laser system based on the model of the geometrically dependent gain coefficient (GDGC) is presented. For the study, the photon density/intensity rate equation in the saturated and unsaturated conditions, along with reported experimental measurements on the ASE output energy and spectral bandwidth for N-2-lasers were utilized. It was found that the GDGC model is able to explain the ASE output energy behavior and gain profiles correctly. In addition, the model was used to predict the spontaneous emission bandwidth Delta nu(0) and consequently the stimulated emission cross-section for the C -> 3 transition of nitrogen molecule at 337.1 nm. In this work, for example, Delta nu(0) was found to be 766 GHz (2.9 angstrom) which is consistent with the earliest experimental observation on the ASE bandwidth reduction in a N-2-laser as reported to be similar to 3. This is the first theoretical result that explains the spontaneous emission bandwidth which is different from the commonly used value of similar to 1 angstrom obtained from measurements of N-2-lasers output spectra. The method was also applied for a filament N-2 laser for the C -> 3 transition produced in atmosphere, and a good consistency between the laboratory and filament lasers was obtained. Details of the calculations for this study are presented. The results obtained from 3-level systems confirm further the potential of applying the GDGC model for the ASE study in different laser systems and is unifying lasers of the same active medium. (C) 2013 Elsevier B.V. All rights reserved.