Measuring the refractive index and thickness of a thin film: an optical polarization experiment

Abstract

Abstract We propose a teaching experiment for simultaneous measurement of the refractive index and thickness of a thin film. The experimental apparatus includes: a diode laser, a polarizer, a spectrometer, a photodiode and a portable digital multimeter. With the apparatus, we measure the refractive index and thickness of two thin films (a silicon dioxide film on silicon, a silicon nitride film on silicon). The maximum discrepancy between the results of our apparatus and an ellipsometer is 1.4%. The experiment described here can be used in optical polarization teaching for undergraduate sophomores and has several valuable pedagogical outcomes: (1) understanding the multi-beam interference in a film; (2) applying chi-square minimization; (3) carrying out the nonlinear curve fitting with multiple parameters.