Structure orientation determined in transmission and reflection: q-plate

TL;DR

This paper presents a microscopy method combining spectral filtering, circular polarization, and 4-polarization imaging to accurately determine the orientation of q-plates in transmission and reflection modes, enhancing anisotropy analysis.

Contribution

It introduces a novel imaging approach using a 4-polarization camera and spectral filtering for precise orientation measurement of birefringent q-plates in both transmission and reflection.

Findings

High-fidelity readout of q-plate birefringence achieved

Effective determination of azimuth orientation in reflection mode

Enhanced anisotropy analysis through combined imaging techniques

Abstract

Determination of orientation in the imaged sample/scene has a large application potential when the anisotropy of properties is analysed, usually, under a linearly polarised illumination. This study combined several improvements of microscopy imaging: use of an incoherent white illumination source (a lamp) with a spectral filter to define a spectral window, a plastic circular polariser to image with circularly polarised light (instead of linear), and a 4-pol. camera with integrated polarisers for simultaneous acquisition of images at four pi/4-azimuth shifts. In the transmission mode, a high-fidelity readout of form birefringent optical elements, q-plates, was achieved using a fitting procedure based on the analytical expression of S0 (intensity) Stokes parameters at the pixel level. In the reflection mode, the S0 fit was used to determine the azimuth orientation of the q-plates, as well as a generic Amp x cos(2Q1 - 2Q0) + Offset fit (at pixel level) applied to images taken at four Q1 azimuths. The 4-pol. analysis in reflection under circularly polarised illumination is discussed.