High-speed portable polarimeter using a ferroelectric liquid crystal modulator

Abstract

The implementation of an imaging polarimeter able to capture dynamic scenes is presented. Our prototype is designed to work at visible wavelengths and to operate at high-speed, ie above 200 Hz, contrary to commercial or laboratory liquid crystal polarimeters previously reported in the literature. It has been used in the laboratory with controlled illumination conditions (wavelength, coherence or incoherence, incidence, …) as well as in a natural environment with sunlight or any lamp or light source. The device consists of commercial components whose cost is moderate. The polarizing element is based on a ferroelectric liquid crystal modulator which acts as a half-wave plate at its design wavelength. The device has been fully characterized and verified to work up to 1 kHz. It produces a 90° polarization rotation. In this Orthogonal State Configuration Imagery (OSCI), images in degree of polarization (DOP) can be obtained with simple postprocessing of two consecutive images. With a commercial CCD camera, operation up to 360 Hz is demonstrated, resulting in images whose quality is equivalent to that of classical low speed polarimeters.

High speed partial Stokes imaging using a ferroelectric liquid crystal modulator

“…An improvement could be to use this imaging analysis matrix instead of the averaged matrix we used, but this would result in either a slower or a more complex computer implementation. The use of a transmissive modulator may be a solution, but to our knowledge, presently, only bistable transmissive modulators were reported in such implementations [35]. This implementation could also be enhanced with the use of a faster camera, since the modulator is only used at 234 Hz, whereas it can reach up to 1015 Hz.…”

Imaging linear polarimetry using a single ferroelectric liquid crystal modulator

“…It can classically consist of running the modulator and the camera at a higher frame rate [28], since this FLC cell was successfully operated in bistable mode at above 2 kHz. Another way consists, as mentioned earlier, in considering the response of the fourth voltage control, provided it is accurately modeled.…”

Cancellation of motion artifacts caused by a division-of-time polarimeter

“…On picture (a) the luminance of the acquired scene is shown. 9 One can distinguish in the foreground a tree, a walking pedestrian and four cars (one is hidden behind the leaves of the foreground tree). And in the background there is a building and several trees.…”