Spectral Analysis of the Amplified Spontaneous Emission in the Second Positive System of the N 2 Molecule

Abstract

The spectrum of the 0-0 band of the ${\text{C}}^3{\Pi }_u\to {\text{B}}^3\Pi g$ electronic transition of the N₂ molecule presents a considerable difference in its distribution of intensities, as a function of the wave number, when the emission spectrum by glow discharge is compared to an amplified spontaneous emission (ASE) regime spectrum, commonly known as the N₂ “laser”. In the present paper, this particularity, due to gain of the transition, is analyzed from an experimental and theoretical point of view, and for the first time has its experimental and theoretical intensities fully compared. An experimental rotational spectrum is obtained for this transition and a model for the ASE intensities has been carried out in order to retrieve the experimental conditions. The theoretical calculations of the gain have been carried out through a model proposed by other authors, as explained in the article. For the comparison among the ASE experimental and theoretical intensities, the fast and slow relaxation approximations proposed have been used, being the first one that best reproduces the experimental spectrum. For the first time, the experimental and theoretical spectra are compared directly, allowing the precise determination of the vibrational coefficient of inversion and temperature, showing the possible problems arising from the approximation. A good agreement between experimental and theoretical results is observed showing the reasonable validity of the model for the gain.