Thermally-guided fiber-rod laser

摘要

Summary form only given. Fiber and bulk lasers form two distinct classes of solid-state laser, both of which have achieved tremendous success in various arenas, but they are not without their limitations. The long, thin geometry of a fiber allows excellent heat dissipation, which combined with a waveguiding structure provides stronger resilience to thermally-induced mode distortions than in bulk lasers, allowing diffraction-limited single-mode operation at multi-kW power levels in continuous-wave mode. However, the threshold for deleterious non-linear effects and laser-induced damage in fibers is generally much lower than bulk systems, owing to very tight beam confinement over a long interaction length, placing stringent limitations on pulsed performance in fibers.In this paper, we investigate an alternative laser geometry occupying a domain that lies between traditional fiber and bulk laser systems. This geometry comprises a fiber-based thin-rod structure, with a diameter on the order of several hundred microns, and with length on the order of several centimetres. The motivation is to combine the advantages of the fiber geometry for excellent thermal management and the bulk geometry for greater immunity to non-linear effects and optical damage, whilst elegantly controlling the laser mode profile using thermally-induced waveguiding. Rare earth ion doped silica is an excellent candidate as the gain medium due to its high fracture limit, positive thermo-optic coefficient and because there are well-established fabrication techniques for producing high purity material with exceptionally low background loss. Thermally-induced waveguides can be tailored to have significantly larger transverse dimensions than conventional `engineered' waveguides yielding potential performance benefits, especially in pulsed mode.