Optical and Quantum Electronics 25 (1993) 695-698 A proposed new experimental setup for determination of refractive indices of liquids by mode line measurements S. P. POGOSSIAN, H. LE GALL CNRS, Laboratoire De Magn~tisme et Mat~riaux Magn~tiques, 1, Place Aristide Briand, 92195 Meudon Cedex, France E. A. ARUTUNIAN, S. Kh. GALOYAN Institute for Physical Research, Armenian Academy of Sciences, 378410, Ashtarak-2, Armenia M. M AAZA Laboratoire L~on Brillouin, Commissariat ~ I'Energie Atomique-Centre National de la Recherche Scientifique, Centre d'Etudes Nucl~aires-Saclay, 91119 Gif-sur- Yvette, France Received 26 February; revised 8 May; accepted 13 May 1993 A new experimental method is proposed for measuring the refractive indices of liquids based on mode line measurements. The experimental setup consists of a dielectric substrate in which a rectangular hollow is formed containing the concerned liquid. This is covered by a trapezium-shaped prism. The liquid, confined between both basin walls and the prism, forms a waveguide. Thus, the refractive index of the liquid can be determined by measuring the propagating modes in the structure. Using this technique, the refractive indices of liquids can be measured to an accuracy of the order of 1 • 10 -4. 1. Introduction There are several conventional methods based on total internal reflection that permit mea- surement of liquid refractive index (LRI). Refractometers of Pulfrich and Abb6 are com- monly used for these measurements. In these two devices, the critical angle of total internal reflection is measured by observing, in a telescope, the limit between the bright and dark fields. Unfortunately, these techniques cannot be used for the determination of refractive indices of absorbing liquids, owing to the blurring of the contrast between the bright and dark zones, which reduces the precision of the LRI determination. This paper deals with a new method for measuring LRI based on mode line measure- ments that provides an accuracy of 1 x 10-4. In contrast to conventional methods that detect the borderline between bright and dark zones, this method measures the angles of mode intensity maxima. 0306-8919 9 1993 Chapman & Hall 695