Hollow sapphire tubing has been used to deliver nearly single-mode CO2 laser energy. The hollow single-crystal A12O3 fiber has an n < 1 cladding at 10.6 µm. Measured losses at 10.6 µm are as low as 0.49 dB/m, and the minimum bend radius of the 580, µm × 380 µm fiber is 14 cm. Bending losses are shown to vary as 1/R, and essentially only the HE11 mode propagates in the bent guide.
© 1990 Optical Society of America
James A. Harrington and Christopher C. Gregory, "Hollow sapphire fibers for the delivery of CO2 laser energy," Opt. Lett. 15, 541-543 (1990)