Light and thermodynamics: the three-level laser as an endoreversible heat engine

TL;DR

This paper introduces a novel temperature scale for analyzing three- and four-level lasers as endoreversible heat engines, enabling new efficiency insights and extending thermodynamic models to laser cooling.

Contribution

It presents a new temperature scale based on mathematical similarity to endoreversible heat engines, applying thermodynamics to laser models for the first time.

Findings

New temperature scale for laser thermodynamics

Application of endoreversibility to laser cooling

Extended theory to four-level laser models

Abstract

In the past, a number of heat engine models have been devised to apply the principles of thermodynamics to a laser. The best one known is the model using a negative temperature to describe population inversion. In this paper, we present a new temperature scale not based on reservoir temperatures. This is realized by revealing a formal mathematical similarity between the expressions for the optimum power generated by an endoreversible heat engine and the optimum output-coupled power from a three-level laser resonator. As a consequence, the theory of endoreversibility can be applied to enable a new efficiency analysis of the cooling of high-power lasers. We extend the endoreversibility concept also to the four-level laser model.