POLARIZED INFRARED REFLECTIVITY OF FLUOROZIRCONATE GLASSES

The detection of longitudinal optic (LO) components of the vibrational modes has been demonstrated for different types of glasses, through t he use of infrared specular reflectivity at oblique incidence. In this work, both natural and polarized infrared radiation have been used in order to measure the reflectance of ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) g lasses at oblique incidence. The series of glasses analyzed contained between 0-25 mol% NaF. LR reflectance was measured for incidence angle s between 10 degrees and 70 degrees off-normal and the near-normal inc idence data using natural light was transformed by Kramers-Kronig anal ysis, in order to yield the LO (and also the transverse, or TO) spectr a. These results are compared with the experimental polarized reflecti vity curves, as a function of the Na content of the glasses and with c alculated reflectance spectra. The experimental detection of LO modes by infrared reflection spectroscopy at oblique incidence appears to be quite general and it has been confirmed for all types of glasses or a morphous thin films studied so far. The p-polarized component of the r adiation is primarily responsible for the LO mode detection.