Single-Crystal Laser-Heated Pedestal-Growth Sapphire Fibers for Er:YAG Laser Power Delivery.

The Er:YAG laser-induced damage (LID) threshold and modal properties of single-crystal sapphire fibers grown by the laser-heated pedestal-growth method have been measured. The lowest loss (~0.4-dB/m) sapphire fibers produce little mode mixing and therefore deliver a near-single-mode output profile if the Er:YAG laser input beam profile is also nearly Gaussian. Normally, however, Er:YAG laser output beam profiles are multimode with numerous high-energy spikes. This leads not only to a multimode output from the fiber but also increased fiber loss that is due to higher-order mode coupling. The results of LID testing give a damage fluence of ~1.4 kJ/cm(2) for 300-mum core-only sapphire fibers at 2.94 mum.