Light polarization states of a cholesteric liquid crystal probed with optical ellipsometry

• A new formulation to calculate the dissymmetry factor g from Stokes parameter S3/S0.
• Dissymmetry factor g was used to obtain the accurate wavelength.
• The ellipsometry is an efficient method to a characterization optical of Ch-LC.

Herein a useful methodology to study optical properties of cholesteric liquid crystals (Ch-LC) is proposed by using the Fourier decomposition ellipsometry technique to calculate the Stokes parameters of transmitted and reflected light in the UV–Vis spectral range. Combining Bragg reflection and optical activity we were able to obtain ∼100% of linear or circular light polarization from the Ch-LC sample using achromatic and non-polarized light source. The photonic bandgap and the polarization components can be controlled with the temperature as a result of alterations in the helix pitch of the cholesteric phase. Finally, it is demonstrated the correlation between the dissymmetry factor (g) calculated via the Stokes parameter S3 and the reflection spectrum. The data revealed that the maximum value of S3 is not coincident with the peak of maximum reflection. The reflected or transmitted light analysis via Stokes parameters obtained by ellipsometry showed an alternative and low cost method for optical characterization in Ch-LC.

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