The Evolution of Output Power and Polarization Modes at Establishing the Stationary Heat Regime in the Two-Mode He-Ne Lasers
Helium-neon lasers of various types are widespread and used in various fields and sectors of economic and scientific activities. The aim of this work was to study the evolution of output and some other laser parameters when setting the stationary working thermal conditions.  The article presents the first part of the study material on behavior of some low-power dual-mode helium-neon lasers in the process of establishing a stationary thermal regime. Several instances of such lasers were studied (from 3 to 6 depending on the experiments). We attempted to understand the causes and evolution of the fluctuations of the laser power output. Also we consider the behavior of individual longitudinal modes amplitude and their polarization in the first 10 to 30 minutes after the start, when the thermal expansion of main laser elements leads to a noticeable change in their output parameters. Experiments and optical circuit systems using polarization and interference devices such as a Wollaston prism, Fabry-Perot and other original devices described.  In this experimental study we investigated output characteristics of multiple instances of a helium-neon lasers dual mode type LGN-207A, LGN-207B ranging from 1 to 2.2 mW, the radiation which has not clearly marked polarization. Even with such a small sample we showed that: a) the emission behavior of different specimens of these lasers in the first 30 minutes, is markedly different from each other; b) there are lasers in which “jump” modes are minimal or non-existent; c) when even small electrical breakdown in the tube or the power supply occurs, polarization characteristics of lasers become chaotic.  We hope that the results will allow experimenters and designers to make more confident selection of laser technology for the acquisition of the measuring instrument and research complexes.