Discrete Thermodynamics of 2-level Laser - Why Not and When Yes

Abstract

The paper explores a possible application of the discrete thermodynamics to a 2-level laser. The model accounts for the laser openness to incoming pumping power and coming out energy with the emitted light. As an open system, a laser should be in open equilibrium with thermodynamic forces, related to both energy flows. Conditions of equilibria are expressed by a logistic map with specially developed dynamic inverse pitchfork bifurcation diagrams for graphical presentation of the solutions. The graphs explicitly confirm the triggering nature of a laser where bistability is manifested by pitchfork ground and laser branches, with the relative population equilibrium values close to 1 and 0 correspondingly. Simulation was run for a 2-level laser emitting light from far infrared to short wave UV. A newly discovered feature of such a laser is the line spectrum of up and down transitions of the laser excitable dwellers, occurring between the laser and the ground pitchfork branches beyond bifurcation point. The density of the spectra lines tangibly increases as the branches approach their limits. Transitions of both types are overlapping in opposite phases. This effect is a new confirmation of the Einstein's prohibition on practical realization of a 2-level laser. Wide enough gaps between the lines of the spectra were also discovered in this research. The gaps are shielding the light irradiation and may be considered as potential areas of control over the 2-level laser emissions.