Determination of complex refractive index using maximum deviation angle through prism

Abstract

Light-absorbing materials are widely used, and their optical properties are an important factor. Snell's law does not hold in materials that partially absorb light. Hence, the optical path in refraction is calculated from Maxwell's law. We used the optical path to obtain the deviation angle when a light passes through a prism made of light-absorbing material. The deviation angle has a local maximum. The deviation angle near the maximum is sensitive to the real and imaginary parts of the refractive index. The local maximum deviation angle and its incident angle are used to determine the complex index of refraction. This measurement has the same advantages as measuring the minimum deviation angle of a transparent prism. The detection is easy. Then, it is necessary to determine the complex refractive index from the measured maximum deviation angle and its incident angle. These two angles are plotted parametrically by varying the real part of the refractive index under a fixed imaginary part. The similar curves are drawn under the fixed real parts. Each curve has a fixed value for the real or imaginary part of the refractive index. Drawings of these many curves are made prior to measurement. Then we select the four curves that are closest to the measured local maximum deviation angle and its incident angle. Four fixed values attached to each of the four curves determine the complex index of refraction. The method in this paper can easily determine the complex refractive index and can be used for material identification.