Full Stokes polarimetry using dual-frequency liquid crystals

Abstract

In a dual-frequency liquid crystal (DFLC), when the frequency of the applied voltage is more than a critical value (f c ), the dielectric anisotropy of the material changes from positive to negative. This causes the director to switch its orientation from parallel to the field (for f < f c ), to perpendicular to it (f > f c ). Hence DFLC can be used in modulating the light by switching the frequency of an externally applied voltage. We present in this work about application of DFLCs in full Stokes polarimetery. A polarization modulator has been worked out based on two DFLCs and two static retarders. The combination of DFLCs' switching and static retarders are chosen such that more or less equal weightage is given to all the Stokes parameters. Initial results on the optimization of position angles of the modulators are presented towards the goal of achieving polychromatic modulator in the wavelength range 600-900 nm.

Instrumentation for solar spectropolarimetry: state of the art and prospects

“…89,199 • Dual-frequency Liquid Crystal (DFLC): DFLC's are a kind of LCVR that are under study to be used in solar polarimetry. 202 The retardance of a DFLC changes between a very low (ide- Table 2. Each labeled dot represents a polarimeter, we use black labels for space, rocket and balloon borne instruments.…”

Development of a liquid-phase microextraction based on the freezing of a deep eutectic solvent followed by HPLC-UV for sensitive determination of common pesticides in environmental water samples

“…The limit of detections (LODs), based on signal-to noise ratio (S/N) of 3 ranged from 0.05 to 0.50 mg L À1 which is much lower than the maximum residues levels (MRLs) established by European Union regulation (ranged from 3-5 mg L À1 for target analytes in drinking water). 38,39 The enrichment factors and the extraction recovery of target pesticides were from 150 to 180 and 75 to 90%, respectively.…”

Binary Solvent Dispersive Liquid-Liquid Microextraction for the Determination of Pesticides in Natural Water Samples

“…These solutions were prepared in 10% (m/v) sodium chloride to raise the ionic strength and facilitate the phase separation due to the salting-out effect. 17,18 Quantities of salt higher than 10% were not used, due to the precipitation of small crystals of NaCl in the interface between the organic and the aqueous phases after the centrifugation step.…”

“…Several techniques have been employed for pesticides determination in water samples, 10 such as solid phase extraction (SPE), 11,12 stir bar sorptive extraction (SBSE), 13,14 and liquid-phase microextraction (LPME) 15 techniques, such as the dispersive liquid-liquid microextraction (DLLME). [16][17][18][19] Developed by Rezaee et al 20 in 2006, the DLLME is a rapid extraction method that provides high recovery rates (especially for non-polar analytes), ease of operation, and also low cost, which is a feature inherent to all liquid-liquid extractions (LLE).…”