At the surface of a metal or in a thin metal film, there exist plasma modes which are distinct from the bulk mode. Some of them can interact with an electromagnetic wave, and cause optical plasma resonances. In this review, optical plasma resonance phenomena in metal films, e. g., plasma radiation, optical plasma resonance absorption and radiative decay of surface plasmons, are surveyed. Finally, optical plasma resonance absorption of island films is discussed.
The propagation of light waves in a cholesteric liquid crystal is very interesting, because of the helical structure of its molecular ordering. We undertook a theoretical analysis based on exact solutions applicable to an arbitrary wavelength, by an extention of Conners' analysisusing Maxwell's equations and rotation matrix. By solving the wave equations for circularly polarized waves, we obtained, theoretically, an anomalous dispersion relation for right-handed circularly polarized waves in a right-handed holesteric material near the total reflection region where anomalous optical rotatory dispersion is experimentally observed. The formula for optical rotatory power derived from our analysis gives more accurate results for all wavelength region than those calculated either by de Vries' theory, which causes large error near the total reflection region, or by Chandrasekhar's theory. The spectral width of the reflected circularly polarized light turns out to be about 250 Å, which yields a good agreement with the experimental value by Fergason.
As a sequel to the previous paper I, in which the wave propagation in an infinite cholesteric material was analyzed, we report in this paper the result of a theoretical study on the ptical properties of a cholesteric liquid crystal of finite thickness. The maximum value of selective reflection was found at the wavelength which is equal to the pitch of the cholesteric structure, and increases to unity with increasing sample thickness. It is noteworthy that there exists no discontinuity in the slope of the curve as in the case for infinite material, and that there appear minor side lobes due to an interference effect. A similar characteristic is also predicted for the circular dichroism. Furthermore, the maimum value of the optical rotatory power decreases with sample thickness, and the interference effect is also present.
Photoconductivity measurements are made on single crystals of Cd4SiS6 which are heattreated in the atmospheres of the constituent atoms (Cd, Si and S). It is found that photoconductivity is strongly affected by the deviations from stoichiometry of Si atom in Cd4SiS6. From measurements of the thermally stimulated current and the effect of the superposition of infrared light on photoconductivity, the values of the electron trap depth are determined. The results obtained by the two methods agree with each other, and it is concluded that this trap is located 0.72eV below the conduction band. This electron trap is annihilated by a heat-treatment in the Si atmosphere. Taking account of the results of transmission and reflection spectra measurements, it is inferred that this electron trap is due to a Si vacancy.
A hybrid waveform processor has been constructed and applied to the deconvolution procedures for correcting the waveform distortion induced by a finite instrumental resolution. The whole system of the processor consists of a small magnetic drum memory and hybrid operational circuits. As is well-known, the numerical deconvolution procedure for practical data usually accompanies some difficulties, because a small experimental error in the observed curves leads to a much larger error in the results. The procedure adopted in this work is the iteration method which is commonly recommended for the processing of experimental curves. The usefulness of the processor for the deconvolution procedure is demonstrated by sharpening a smeared band or separating overlapped bands in infrared absorption spectra. Besides the experimental details, an extensive discussion is also made on the error due to the inaccurate setting of the instrumental function.
Infrared (3.39 μm) laser patterns of very weak output power can be observed on a thin plastic film coated with cholesteric liquid crystals. Minimum laser power detectable with a liquid crystal having the response temperature width of 0.65°C is about 20 μW, which corresponds to an irradiance of 1. 1 mW/cm2.