Optical Constants of Potassium Bromide in the Far Infrared

Abstract

One of the fruits of the recent developments in far-infrared techniques has been the knowledge of the whole vibrational spectrum of a solid and its evolution with temperature, We consider here the particular case of potassium bromide, which has been studied elsewhere by neutron diffraction, and we give all the information obtained in the laboratory by the diferent methods of far-infrared spectrometry now available:(1) the reflectivity of potassium bromide at liquid-helium, liquid-nitrogen, and room temperature, including the effect of polarization, grazing incidence, and the quality of the surface, and interpreted according to a Kramers-Kronig analysis and a Lorentz analysis with two linear damped oscillators; (2) the transmission of thin layers at, normal and oblique incidence, and a determination of the complex index of refraction, the compressibility coefficient, and the effective charge of the ions; (3) the very-far-infrared transmission of thick samples and its temperature dependence explained by phonon-diGerence processes; and (4} the 6rst spectroscopic observation of the phonon spectrum of an ionic crystal, provided by sodium-induced absorption in potassium bromide, with peaks at 101, 83.5, and 71.5 cm, having the same frequencies as the three maxima in the lattice-mode density, which correspond approximately to characteristic TQ, LA, and TA phonons, The effect of other impurities and of neutron irradiation is also considered.

Phonon Response in the Infrared Region to Thickness of Oxide Films Formed by Atomic Layer Deposition

“…Also, the experimental absorptance data (not shown) exhibit a significant change in slope as expected from the simulation data obtained using the FKP method. From the agreement between absorbance and absorptance data, we infer that, at constant temperature, 49 phonon absorbance saturation in transmission configuration above the Berreman thickness is due to the limited field penetration depth 50 and absorption of IR radiation into the oxide layer. 41,49,51,52 This picture is analogous to skin depth in metals interacting with low frequency electromagnetic waves.…”

“…The saturation of surface LO4 mode absorbance for t larger than the Berreman thickness is related to the nature of surface LO modes, which absorb IR energy. 18,40,41,51 The behavior of surface LO mode absorbance with film thickness can be explained in two ways: (1) by the limited field penetration depth 50 of IR radiation into the oxide layer, 27,41,49,51,52 or (2) by the superficial nature of the surface LO modes. [12][13][14][15][16][17][18]53 The surface LO4 mode absorbance saturation is included in both Hansen and FKP formalisms because as t!0, the frequencies of TO phonons and surface LO modes are related as optical phonons in the bulk by the Lyddane-Sachs-Teller relation.…”

Underdamped longitudinal soft modes in ionic crystallites—lattice and charge motions observed by ultrafast x-ray diffraction

“…The analysis of the spectra described in detail in Appendix A gives the frequency-dependent phase change relative to the phase calculated with the dielectric function from Refs. 14 and 31 [panel (b)]. For all KDP concentrations, there is a zero crossing at 0.55 THz, pointing to an absorptive resonance in the imaginary part of the dielectric function of KDP.…”

“…Black dashed line: expected oscillations according to (A9) for the 20-mg pellet calculated from the transmission of the pure KBr pellet and dielectric functions from Refs. 14 and 31 . (c) Zoom of the frequency range at which the amplitude change and phase shifts between data and expected oscillations are more obvious.…”

Spectres de réflexion et constantes optiques de la proustite (Ag 3AsS3) entre 14 et 600 cm-1 a 300 k et 80 k

“…facteur de reflexion R * a 300 K et a 80 K pour les deux orientations de la polarisation. A basse temperature, on constate le phenomene habituel [4] de renforcement des maximums et leur deplacement vers les hautes frequences.…”