Regular Article

Criticality of depth of intensity modulation and simulation of refractive index profile in thermal lens technique

Department of Optoelectronics, University of Kerala, Trivandrum 695581, Kerala, India

^* e-mail: drssraman@gmail.com

Received: 30 January 2020
Received in final form: 14 April 2020
Accepted: 17 April 2020
Published online: 11 June 2020

Abstract

The present paper intends to unveil the criticality of the depth of intensity modulation (D) in getting correct results in optical experiments employing electromechanical choppers. The study elucidates experimentally using a single beam thermal lens setup with an optical chopper with variable D, designed and constructed cost-effectively, and also by simulating the refractive index profile generated within the medium. The thermal diffusivity of water with a trace amount of chlorophyll is determined by varying D for a given period. It is observed that for a D above 10%, photodissociation and Soret effect significantly affect the thermal lens signal and thereby giving erroneous value to the thermal diffusivity. The UV-visible spectroscopic analysis reveals reduced absorption for the leaf pigments − chlorophyll a, chlorophyll b, and lutein as a result of photodissociation. Thus the study demonstrates the criticality of D for obtaining error-free measurements.