Growth And Optical Properties Of Single-Crystal Sapphire Fibers

Abstract
Sapphire single-crystal fibers are very promising for applications in high power laser delivery systems operating in the mid-infrared, e.g. the Er:YAG line at 2.9 μm. The fibers are nontoxic and chemically resistant. Also, they are mechanically strong and can be bent to a radius of less than 10 mm without breaking. Fibers with diameters of 110 μm and lengths of up to 1 m were grown by the laser-heated pedestal growth method. The minimum loss of 0.5 dB/m was measured in the near infrared at 1064 nm. An absorption band centered at 400 nm resulted in losses of up to 20 dB/m. Absorption loss at the Er:YAG line is 0.88 dB/m for a fiber grown in an atmosphere of pure oxygen. A damage threshold higher than 1.2 kJ/cm2 was measured for 110 μs long pulses, making tissue ablation feasible with fibers several meters long.