Abstract

Broadband tunable solid state lasers in the 1300-1600 nm spectral region are required for applications in remote sensing, eyesafe optical ranging and communication. However, with Cr:YAG, the most promising tunable laser material in this region¹, acute problems of output energy saturation, rollover in efficiency and thermal limitations have been observed. These problems have been attributed to ground state bleaching, pump and laser excited state absorption (ESA) and thermal lensing. Here we report, to our knowledge, the first measurements of thermal lens strength in Cr: YAG. Focal lengths have been determined under a range of pump conditions with a conventional low Cr⁴⁺ concentration (0.2at.%) rod, and with a new heavily-doped (0.3at.%) rod. These results have been incorporated in a dynamic spatio-temporal model of gain-switched Cr:YAG lasers. The good agreement which has been obtained between model predictions and experimental results confirms the role of both thermal lensing and parasitic ESA loss processes in the saturation, rollover and instability problems. Results of the model have been used to maximise Cr:YAG output at a range of pump repetition rates, and can be used to optimise cavity design for specific rod parameters and pump fluence.

© 1998 IEEE