It is shown that the spectra given by the difference between the reflectivity for p-polarized light and the squared reflectivity for s-polarized light (Rp−Rs2) with an angle of incidence of 45° can be used for directly determining the frequencies of zone-center transverse optical (ωTO) and longitudinal optical (ωLO) phonons in very thin polar-semiconductor films on substrates. These spectra are also useful for measuring resonance frequencies of both transverse and longitudinal optical confined phonons in ultrathin layers of superlattices.

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The quantization of the exciton translational motion in CuCl thin films, having a thickness much less than the photon wavelength and overlying a substrate, is theoretically investigated by employing the 45° reflectometry. We show that the resonances associated with quantized longitudinal excitons can be directly measured by means of such a polarization-modulation technique despite the relatively large damping factors for very thin films.

The optical response of near-surface localized excitons and their corresponding quantized longitudinal polarization waves in thin semiconductor films on substrate is investigated theoretically. The identification of resonances associated with such longitudinal modes in simple spectra of reflectivity for p-polarized incident light (Rp) is rather difficult because of the large damping factor for a thin film near the longitudinal frequency (ωL) and a background contribution to Rp. However, as is shown here, the quantized longitudinal polarization waves manifest themselves more clearly in spectra of 45° reflectometry, which is based upon the measurement of the difference between the reflectivity Rp and the squared reflectivity for s-polarized light (Rs2) with an angle of incidence of 45°.

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