Entropy balance of optically pumped cw lasers

The entropy emitted from cw lasers is derived. It is found that the entropy flux does not depend on the pump power. The entropy fluxes of two lasers with and without coupled cavities are discussed, It is shown that the entropy per unit power is reduced by coupling two resonators. The fundamental thermodynamic efficiency limit of optically pumped cw lasers is shown to be typically almost unity. The minimum fundamental fraction of total power loss for a typical diode pumped laser is found to be of the order of 10(-8). (C) 1998 Elsevier Science B.V.