Amplitude Sensitive Optical Heterodyne and Phase Lock-in Technique on Small Optical Rotation Angle Detection of Chiral Liquid

Abstract

A novel method in which an optical polarized heterodyne polarimeter and lock-in technique are used to measure low concentration glucose solution based on the detection of an amplitude sensitive heterodyning signal is proposed. The linearity and the sensitivity of the measurements are enhanced in comparison with those of conventional methods in which a Pockels cell, Faraday rotator, and rotating linear polarizer are used to modulate the incident light source. A pseudo heterodyning carrier and delayed optical heterodyning technique is also discussed in comparison with the proposed amplitude sensitive optical heterodyne method. During the detection of glucose solution, the measurable rotation angle reaches 10-4 deg and a sensitivity of a concentration to 10 mg/d l in 1 cm optical path length is obtained. Further improvements such as using a better intensity stabilized laser and a high extinction ratio Glan-Thompson polarizer will allow the detection sensitivity of the measuring optical rotation angle to reach 10-5 deg.