The absorption spectra of fused-silica samples, selected for their “typical” optical properties, are presented. The ultraviolet absorption edge shifts some 30 mµ toward the ir, between 22° and 982°C sample temperatures. In the same range, the 1.4-µ absorption peak passes through a maximum in absorption and the 2.23-µ peak passes through an absorption minimum; both move toward the ir. The water band at 2.75 µ shifts first toward the uv, then toward the ir, with increasing temperature, while monotonically decreasing in absorption.
OLIVER J. EDWARDS, "Optical Transmittance of Fused Silica at Elevated Temperatures," J. Opt. Soc. Am. 56, 1314-1319 (1966)