Abstract

Traditional solid-state amplifiers or lasers are exothermic. Heat generated inside an amplifier or a laser medium, which is caused by the quantum defect, is a source of increased temperature and stress. It causes poor beam quality and limits the average output power. The very high surface-to-volume ratio and guiding in optical fiber amplifiers and lasers provide an excellent solution, which can compete with other high-power laser technologies based on solid-state bulk lasers, for example thin-disk lasers. However, today heat transport remains a problem at very high powers. The idea to cool solids with anti-Stokes fluorescence was first proposed by Pringsheim in 1929 [1]. In 1995, Epstein’s research team observed for the first time the net radiation cooling by anti-Stokes fluorescence in solid state materials [2]. In 1999, Dr. Bowman proposed a radiation-balanced (athermal) laser, in which lasing is accomplished by offsetting the heat generated from stimulated emission by cooling from anti-Stokes emission [3]. This scheme has a single pump source for both the amplification and cooling processes. Two manifolds of active ions, the ground and the first excited manifold are involved in both the cooling and the amplification processes. The athermal operation in this scheme can be realised only if the pump wavelength, λ_P, obeys the inequalities λ_F < λ_P < λ_S, where λ_F is the mean fluorescence wavelength of active ions, and λ_S is the wavelength of the amplified or laser signal, and the value of the pump power is properly arranged along the length the active medium. Unfortunately, the power of the amplified signal increases only linearly along the length of the gain medium in this scheme. This results in the considerable increase in the length of the active medium in comparison with traditional amplifiers or lasers.

© 2011 Optical Society of America