Spectrophotometric studies of ultra low loss optical glasses. I. Single beam method.

A double beam spectrophotometer is described, suitable for the measurements of very low attenuation coefficients in glass in the wavelength range 500-1000 nm. The instrument is shown to have a balance stability of ±1 × 10−5. The systematic errors involved in the use of the long samples required for these measurements are studied. The instrument is shown to be satisfactory in making measurements of attenuation coefficients of 00001 cm−1 with an accuracy to ±0000 01 cm−1 when sample pairs of 20 cm length difference are used. Results of measurements on very low loss silica, which illustrate the performance of the instrument, are given.