Knowledge Bank

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 $d2R/d\lambda 2=0$. In particular the $\lambda TOs$ correspond to points where $d2R/d\lambda 2=0$ and whereas the $\lambda LOs$ correspond to points a where $dR/d\lambda =0$ but $dR/d\lambda >0$. A simple heuristic argument shows that this method will work to the same extent that $Chang\prime s1$ method is valid. Differential reflection spectra of $Al2O3.MgAl2O4.Al23O27N5(ALON)$ and $Y2O3$ will be presented. In most cases well defined peaks are obtained making the determination of the optical mode frequencies straight forward.