Models of Geometrically "Stabilized" Laser Cavity

The Lamb-dip characterizing the line shape emitted by a gas laser is often used in spectroscopy of materials as a reference for frequency measurements. For such lasers, the frequency control is performed on the Lamb-dip. It is therefore essential, for accurate measurements, that its frequency matches with the laser resonance frequency. This is only possible if the emitted line shape is symmetrical, which is not usually the case. Indeed, the lens effects induced in the laser amplifying medium, which are due to the population and the saturation inhomogeneities, generally produce an asymmetrical emitted line shape. So, the frequency of the Lamb-dip is shifted compared to the central frequency. In this work, we will first revisit the model given in the literature, in order to highlight the limit of its validity, and then we will propose through an appropriate choice of the cavity geometry, a "stabilized" cavity model giving rise to a symmetrical line shape even when the control parameters vary.