A simple method to measure critical angles for high-sensitivity differential refractometry

S C Zilio

doi:10.1364/oe.20.001862

Abstract

A total internal reflection-based differencial refractometer, capable of measuring the real and imaginary parts of the complex refractive index in real time, is presented. The device takes advantage of the phase difference acquired by s- and p-polarized light to generate an easily detectable minimum at the reflected profile. The method allows to sensitively measuring transparent and turbid liquid samples.

Highlights

The measurement of critical angles in total internal reflection (TIR) has found increasing use in differential refractometry, for absorbing or turbid samples [1,2,3,4]
McClimans et al [5] demonstrated a technique for measuring the refractive index of transparent liquid samples at a sensitivity level of 10−6 by using a divergent laser beam, polarized parallel to the plane of incidence (p-polarization), and a linear diode array to precisely find the critical angle
Since in this example α = 0, one can determine the critical angle in a condition of zero-signal, which completely avoids the problem of laser fluctuation

Summary

Introduction

The measurement of critical angles (θc) in total internal reflection (TIR) has found increasing use in differential refractometry, for absorbing or turbid samples [1,2,3,4]. This occurs because the measurement is carried out in the TIR condition where the reflected light is intense. This method promptly provides the values of the refractive index and extinction coefficient in real time, without any complicated fitting procedure

Experimental section

Origin of the dark stripe

Results and discussion

Conclusions