Showing papers on "Total external reflection published in 1973"

Method for the determination of the index of refraction of particles suspended in the ocean

Abstract: It is shown that the complex index of refraction of a given particle-size distribution may be calculated if the particle extinction coefficient and the particle absorption coefficient are known. If the particles are assumed to be nonabsorbing, a real index of refraction may be calculated from the ratio of light scattering at 45° from the forward for two wavelengths. Application of the method to two stations off Ecuador indicates that the particle index of refraction can be determined with sufficient accuracy to become an important parameter in the study of the oceans.

Measurement of thin films by optical waveguiding technique

Abstract: In order to measure the thickness and refractive index of a transparent thin film on a substrate of higher refractive index, such as a film of silicon oxide on a substrate of silicon, an optical wave is coupled into and guided through the film. The guided wave is coupled into the film by means of the phenomenon of the tunneling into the film of an evanescent wave from a beam of light incident on the surface of an adjacent coupling medium at an angle greater than the critical angle for total internal reflection in the medium. The intensity minima of the optical radiation which can be coupled out of the film back into the coupling medium (overall reflection), as a function of angle, yields data from which the desired thickness and refractive index can be determined.

Emittance of Semi-Infinite Absorbing and Isotropically Scattering Medium with Refractive Index Greater Than Unity

Abstract: An approximate solution is presented for the integrodifferential equation that governs the radiant intensity and the source function within a semi-infinite absorbing-scattering medium with an index of refraction different from unity. The exponential kernel substitution has been used to develop a closed form analytical expression for the directional emittance as a function of the refractive index and the scattering albedo. The scattering has been considered as isotropic, and the Fresnel relations have been used to evaluate the reflection and the transmission at the interface. The directional and the hemispherical emittances are presented for a refractive index range between 1 and 2 and for scattering albedo between 0 and 1. The results indicate that the directional and hemispherical emittances of a medium with a refractive index larger than unity can be either smaller, because of interface reflection, or larger, because of scattering, than that associated with a medium of a unity index of refraction. A generalized graph is presented from which an approximate value for the directional emittance can be obtained for a wide range of optical conditions. Based on other applications in the field of radiative transfer with similar geometry and on comparison, when possible, with exact solutions, the approximate method which has been used should be accurate in predicting directional and hemispherical emittances to within 10%.

Light‐wave coupling to optical waveguides by a tapered cladding medium

Abstract: A transition from a symmetric to an asymmetric waveguide can serve as a mode‐ and polarization‐dependent light‐wave coupler. Coupling experiments with an efficiency up to 70% are reported. Furthermore, total reflection occurs at the transition if the angle of incidence of the guided wave exceeds a critical value. Coupling and total reflection are explained, using the concept of the effective refractive index.