ABSTRACT
This chapter outlines the various ways in which temperature affects lasers, and to model those effects. Four-level lasers are generally unaffected by temperature change, but four-level lasers with a Lower lasing level particularly close to ground level are affected. It is ironic, then, that the quasi-three-level lasers, which offer the highest efficiencies, are also those most affected. The chapter examines the materials in detail, and presents models to determine the effect of temperature change on laser output. In a three-level laser, such as a ruby, loss due to absorption of photons can be quite large. Imagine an unpumped ruby amplifier such that essentially all atoms of chromium will be at ground state. In a three-level laser, it is obvious that absorption at the lasing wavelength is enormous and so has a drastic effect on the minimum pump power required to achieve lasing action. However, four-level lasers have no such problems with absorption of laser energy.
