ANALYSIS, MEASUREMENT AND OPTIMIZATION OF THRESHOLD POWER OF 3.5 MU-MZBLAN-GLASS FIBER LASERS

A 3.5 mum fiber laser with low threshold power using a 12 cm long, 1 m ol-% Er3+-doped ZBLAN fiber with core radius a = 5 mum and numerical a perture of 0.4 has been developed. The fiber laser was pumped at 650 n m with an Ar-laser-pumped dye-laser. The measured threshold power of 7 6 mW is 13 times lower than our previously reported value of 996 mW. T he improvement is in good agreement with the theory developed in this paper. On the basis of this theory we show how the threshold power can be further reduced by optimizing the fiber design. The theory may be generally applied to mid-infrared fiber lasers pumped at short wavelen gths.