Abstract

Results of studying low absorption plus scattering losses in pure glasses' bulk by direct attenuation measurements with very small numerical aperture NA_g = 0.006 ÷ 0.012 in reflected laser radiation at λ = 632.8 nm are presented. In all studied glasses, including Corning-7940, an order of higher attenuation related to the same coefficient in fibers with NA_f = 0.4 was observed. Experiment indicates the presence of essential small–angle scattering within the direction between NA_f and NA_g. Mean losses were about 80 dB/km at NA_g =0.006 and 40 dB/km at NA_g = 0.012. There are large inclusions compared with laser wavelength, and so higher attenuation (up to 120–200 dB/km) was found in vacuum pressure deposited quartz glass with low OH⁻ content. In unclad fiber with NA_f = 0.4 drawn from the last samples the total losses at λ = 1.3 and λ = 1.55 μm consisted of 1.6 and 0.9 dB/km, correspondingly. The lowest bulk attenuation found at NA_g = 0.006 in fused quartz KV for region VI in 10 cm long sample that consisted of 16 ± 1 dB/km at a surface reflectance stability ±0.005%/h.

© 1992 Optical Society of America