PRECISION LASER-BASED CONCENTRATION AND REFRACTIVE-INDEX MEASUREMENT OF LIQUIDS

Measurement of liquid concentration is important in fields such as che mical analysis and processing, diagnostics, and semiconductor manufact uring. This work presents a high-precision, noncontact, laser-based te chnique to measure the refractive index of liquid mixtures and solutio ns, which can be used to determine the concentration of a mixture. The technique can resolve extremely small changes in concentration, on th e order of 0.01%. The essential components in the system include a HeN e laser as the light source, a precision glass cuvette as the liquid c ontainer and optical cell, and a very-high-resolution position sensor and high-precision digital voltmeter. The experimental configuration i s small, reliable, and inexpensive. Results are presented for ethanol- water and methanol-water mixtures and two cater-salt solutions, with v ery good agreement found between measured values and those reported in the literature.