Some optical, dielectric and lattice properties of three alkaline earth fluorides (calcium, strontium and barium fluorides) and of two other isomorphous fluorides (cadmium and lead fluoride) are reported. Results obtained from experimental studies on infrared and Raman spectra give the fundamental transverse and longitudinal optical lattice mode frequencies, the two-phonon absorption spectra, and the spectra associated with U centre absorptions. Calculations of phonon dispersion curves, density of states and density of com­bined states functions, have been made for all five crystals and these are compared with the experimental results.

A determination of the optical constants of a bulk specimen may be made by measurement of the intensity reflected from the surface of the specimen for at least three angles of incidence. None of the incidence angles needs to be equal to 90 degrees , although when one is, this can be equivalent to the case when the incident intensity is measured. The accuracy with which the optical constants may be determined depends on the choice of the three angles as well as on the accuracy of measurement of the reflected intensity. Results are presented that indicate a suitable choice of angles for unpolarized incident radiation.

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