The influence of the transport of excited atoms on the laser amplification inside the positive column of a low-pressure He-Ne dc discharge of a ring laser gyro has been studied. Both non-radiative diffusion and the contribution of radiation transport have been considered. The transport induced by the radiation trapping has been determined using a Monte-Carlo simulation, taking into account an isotopic structure for the neon and the collisional line broadening in presence of helium. The transfer matrix for spatial redistribution has been calculated in a cylindrical geometry and has been included in a one-dimensional collisional-radiative model (1D-CRM). This 1D-CRM has been used to determine the laser gain within a two levels approach. Our results show that radiative and non-radiative diffusions have a significant contribution on the radial profile of the gain of the main oscillating mode, both in the unsaturated and saturated regimes. This contribution is strongly dependent on the ratio between the transverse sizes of the laser and of the plasma.

A global modeling of a He-Ne ring laser gyro (RLG) has been developed. The physical model of the positive column of the DC discharge includes a fluid description of the plasma, a collisional radiative model (1D-CRM) for the dynamics of excited atomic states and a Maxwell-Bloch calculation of laser amplification. In the present paper we use this global modeling to analyze the influence of the radial transport of excited states, through diffusion and radiative transfer, on the radial profile of the laser gain. Concerning radiative transfer, a full matrix transfer has been determined using a Monte-Carlo calculation and introduced in the 1D-CRM. Using this code, we have analyzed the influence of the boundary condition for the diffusion equation at the capillary walls on the metastable atom densities and on the laser gain.