Optical absorption of rare-earth-doped BeF2 glasses

BeF2 glasses are potentially useful materials for light transmission in the near infrared region of the spectrum. While the intrinsic attenuation of BeF2 is thought to be much lower than silica, the optimum wavelength will be further in the infrared, near 2.1 μ. In this spectral region impurities other than transition metals may be important—rare earths, for example. The data required to estimate the contributions to attenuation are normally not available; hence it is the purpose of the present work to provide that information. Using a binary BeF2/ThF4 glass, the optical absorption spectra of a number of rare earths are measured. The experimental procedures, optical spectra, and absorption strength are described.