DIFFERENTIAL REFLECTION SPECTROSCOPY: A DIRECT DETERMINATION OF LONG WAVELENGTH OPTICAL MODE FREQUENCIES IN POLAR CRYSTALS
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Date
1987
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Ohio State University
Abstract
To the best of our knowledge, no simple scheme has been proposed for a direct determination of optical mode frequencies from observations of reflectivity, R, without detailed curve fitting. It is our purpose to suggest such a scheme. We shall work in the wavelength, $\lambda$, domain. We propose that the transverse optical wavelength ($\lambda_{TO})$ and Longitudinal optical wavelengths ($\lambda_{LO})$ correspond to those points where $dR/d\lambda = 0$, is an extrema, that is where $d^{2}R/d\lambda^{2} = 0$. In particular the $\lambda_{TO}s$ correspond to points where $d^{2}R/d\lambda^{2} = 0$ and $dR/d\lambda < 0$ whereas the $\lambda_{LO}s$ correspond to points a where $d R/d\lambda = 0$ but $dR/d\lambda > 0$. A simple heuristic argument shows that this method will work to the same extent that $Chang's^{1}$ method is valid. Differential reflection spectra of $Al_{2}O_{3}. MgAl_{2}O_{4}. Al_{23}O_{27}N_{5} (ALON)$ and $Y_{2}O_{3}$ will be presented. In most cases well defined peaks are obtained making the determination of the optical mode frequencies straight forward.
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$^{1}$ I.F. Chang, et.al. Phys. Status Solidi 28, 663 (1968)
Author Institution: The Johns Hopkins University, Applied Physics Laboratory
Author Institution: The Johns Hopkins University, Applied Physics Laboratory