Single-crystal YAG fiber optics for the transmission of high energy laser energy

Single-crystal (SC) fibers have the potential of delivering extremely high laser energies. Sapphire fibers have been the most commonly studied SC fiber and the losses for sapphire fibers have been as low as 0.4 dB/m for a 300micron core-only fiber at 3 microns. In this study we report on the growth of SC yttrium aluminum garnet, Y3Al5O12 (YAG) fibers from undoped SC source rods using the Laser Heated Pedestal Growth (LHPG) technique. The advantage of YAG over sapphire is the slight improvement in IR transmission of YAG. The IR transmission of bulk YAG has been shown to extend to 5 μm where the absorption coefficient is 0.6 cm. The garnet family of crystals is one of the most commonly used oxide crystal hosts for lasing ions in high power solid-state lasers, with the most commercially common laser host being YAG. Thus, it is reasonable to assume that YAG fibers will have high laser damage thresholds. The optical losses for 400-μm diameter YAG fibers have been measured to be about 3 dB/m at 2.94 μm. The longest length of YAG fiber grown has been about 60 cm.