Snapshot circular dichroism measurements.

Oriol Arteaga,Zoubir El-Hachemi,Razvigor Ossikovski

doi:10.1364/oe.27.006746

Abstract

Two coherent waves carrying orthogonal polarizations do not interfere when they superpose, but an interference pattern is generated when the two waves share a common polarization. This well-known principle of coherence and polarization is exploited for the experimental demonstration of a novel method for performing circular dichroism measurements whereby the visibility of the interference fringes is proportional to the circular dichroism of the sample. Our proof-of-concept experiment is based upon an analog of Young's double-slit experiment that continuously modulates the polarization of the probing beam in space, unlike the time modulation used in common circular dichroism measurement techniques. The method demonstrates an accurate and sensitive circular dichroism measurement from a single camera snapshot, making it compatible with real-time spectroscopy.

Highlights

Circular dichroism (CD) is the differential absorption of circularly polarized light
In the early realizations of spectroscopic CD measurements from 1960’s [3], the polarization modulation was accomplished with electrically driven Pockels cells, but nowadays virtually all commercial CD instruments use photoelastic modulators
In this work we present a novel method for spectroscopic CD characterization that is based on spatial rather than on temporal polarization modulation

Summary

Introduction

Circular dichroism (CD) is the differential absorption of circularly polarized light. The method we propose is not based on diffraction orders but rather on the coherent superposition of two beams with orthogonal polarizations, that results in an spin-dependent redistribution of light intensity in the transverse plane. It uses a thin doubly refracting crystal slab as a key optical element creating an analog of Young’s double-slit experiment [17] according to the well known interference-polarization laws of Fresnel and Arago [18,19,20]. In what follows we describe the principle of operation of the novel technique, as well as its proof-of-concept spectroscopic implementation in the form of a simple, low-cost setup capable of measuring CD and we compare it with conventional instruments using the time-modulation approach

Principle of operation

Proof-of-concept experiment

A CDE DFDGH

Calibration and evaluation of coherence

CD measurement

Conclusion