Radiation-balanced thin-disk laser system

摘要

Traditional solid-state lasers are exothermic. The quantum defect between the pump and laser photons is a source of heat generated inside a laser medium. Heat generation results in increased temperature and stress in the laser medium, poor beam quality, and limits the average output power of the laser. Thin-disk and optical fiber lasers with their very high surface-to-volume ratio and guidance properties are excellent solutions for reducing heat generation. However, heat transport continues to remains a problem at very high powers, even in these lasers. 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, Bowman [3] proposed a radiation-balanced (athermal) laser, in which cooling with anti-Stokes fluorescence completely offset the heat generated by the quantum defect. In 2002 the first operation of a bulk radiation-balanced solid state laser was experimentally demonstrated [4]. For athermal operation, the pump wavelength, λP, has to be chosen between the mean fluorescence wavelength, λF, and the wavelength of the laser emission, λL, that is λF <λP< λL. In addition, the pump power has to be properly arranged at each point along the length of the laser rod. The precise control of the pump intensity at each point along the gain medium is essential for athermal operation of the laser, but this is extremely difficult to achieve with high accuracy [4].