Generalized channeled polarimetry

Abstract

Channeled polarimeters measure polarization by modulating the measured intensity in order to create polarization-dependent channels that can be demodulated to reveal the desired polarization information. A number of channeled systems have been described in the past, but their proposed designs often unintentionally sacrifice optimality for ease of algebraic reconstruction. To obtain more optimal systems, a generalized treatment of channeled polarimeters is required. This paper describes methods that enable handling of multi-domain modulations and reconstruction of polarization information using linear algebra. We make practical choices regarding use of either Fourier or direct channels to make these methods more immediately useful. Employing the introduced concepts to optimize existing systems often results in superficial system changes, like changing the order, orientation, thickness, or spacing of polarization elements. For the two examples we consider, we were able to reduce noise in the reconstruction to 34.1% and 57.9% of the original design values.

Bandwidth and information in the design and analysis of polarimeters

“…39 We already know that the X-shooter can provide arbitrarily fine spectral resolution when used as a time-modulated instrument (i.e. ignoring the spectral channels completely).…”

“…One of the key observations made by Alenin is that optimal systems generally have PSGs and PSAs that produce modulatns that are independent in their channel structures. 39 …”

Instrumentation for solar spectropolarimetry: state of the art and prospects

“…207,[221][222][223][224][225][226] These novel concepts have not seen similar proliferation in solar polarimetry, mainly because the realization of a system that can image an extended solar target with competitive spectral and spatial resolution, FOV and polarimetric sensitivity has not been demonstrated. Two popular techniques are (a) Channeled polarimetry 225,227 which can be used to encode the input Stokes parameters either into intensity variations of the output spectrum 222,224 or into a set of spatial fringes. 207 The polarization information is commonly retrieved via reconstruction algorithms that involve fitting the imaged observables.…”

An overview of polarimetric sensing techniques and technology with applications to different research fields

“…For modulations that are more densely sampled in terms of sine/cosine curves, their orthogonality indicate to what extent the modulation is optimal. 39 The single sine curve to measure degree and angle of linear polarization is of course well known for a rotating polarizer or a rotating half-wave plate system, but it can also be realized in the spectral domain 37 or in the spatial domain. 35,51 One could even argue that micropolarizer arrays constitute the critically sampled version of such spatial sinusoidal modulation.…”