Caracterização da instabilidade da polarização do laser He-Ne

Abstract

In this work, we investigated the instability of the polarization of He-Ne lasers seeking to characterize and understand the mechanisms behind this behavior. The He- Ne laser was the second demonstrated and created in story and the first to have a gaseous active medium and also to operate in continuous mode. It is a 4-level laser with emission around 632.8 nm, resulting from the amplification of stimulated emission produced by Ne atoms. In experiments two commercial He-Ne lasers with nominal power of 0.5 mW and 1.2 mW and with random polarizations were used, according to manufacturers' information. Measures of intensity versus time with and without a polarizer in front of the laser beam were performed. Without polarizer was observed an initial transient after which the intensity tends to a constant value. With the presence of the polarizer, it was observed that the intensity has a generally sinusoidal periodic behavior and the distance between the peaks of intensity increases exponentially with time. It has been proposed that the intensity variation was due to variation of the polarization of the laser, instability inherent to its construction, probably resulting from a variation in the cavity length with temperature and / or competition among modes of oscillation after the amplification process. Analyzing in detail the measures of intensities was also possible to propose that the behavior of the laser presents three distinct features from the investigation of the temporal evolution of the distances between the peaks. A theoretical calculation that took into account the variation in cavity length with temperature was carried out and compared with experimental data. Finally, a theoretical modeling was done taking into account two possible modes of the Field with circular and elliptical polarizations out of the cavity. In this case the numerical results differed somewhat from the experimental results probably indicating that the model was oversimplified.