Broadly tunable Cr4+ doped solid-state lasers in the near infrared and visible

This manuscript provides a comprehensive review of the characteristics of Cr4+-doped solid-state lasers which produce broadly tunable coherent radiation in the near-infrared region of the electromagnetic spectrum between 1.13 and 1.63 mum. Cr4+-doped gain media have several - favorable characteristics including broad absorption bands that overlap with the operating wavelengths of several commercial pump lasers, a 4-level energy structure that allows continuous-wave as well as pulsed operation with low threshold pump powers, and the presence of broad amplification bands for the generation of ultrashort optical pulses. In addition, non-linear frequency conversion schemes can be readily employed to construct broadly tunable coherent visible sources based on Cr4+-doped gain media. These favorable features make Cr4+-doped lasers potentially important in many applications in optical communications, eye-safe imaging, medicine, and spectroscopy. After a description of the basic physical mechanisms that lead to broad emission in tunable solid-state lasers in general and Cr4+-doped gain media in particular, the manuscript provides a detailed description of the operational characteristics of Cr4+-doped lasers, including rate-equation analysis of power performance, role of thermal effects, and different mode-locking techniques for the generation of ultrashort optical pulses. Later sections focus on the work performed in the development and characterization of specific examples of Cr4+-doped lasers. Particular attention is given to Cr4+ :forsterite and Cr4+ XAG laser systems due to their superior power performance. Gain-switched, continuous-wave, and mode-locked operations of these lasers are described with a particular emphasis on recent developments. Studies carried out with other Cr4+-doped lasers such as Cr4+ :Y2SiO5, Cr4+-doped oxyapatite, Cr4+- doped garnets, and Cr4+:Ca2GeO4 are also described. Finally, use of non-linear conversion schemes in the generation of visible radiation with Cr4+-doped lasers is discussed. In particular, experiments that have been performed with pulsed and continuous-wave Cr4+:forsterite lasers to generate broadly tunable radiation in the 565-685 nm range of the electromagnetic spectrum are reviewed. (C) 2003 Elsevier Science Ltd. All rights reserved.