IMaX: a polarimeter based on Liquid Crystal Variable Retarders for an aerospace mission

Abstract

IMaX is the Imaging Magnetograph eXperiment, an instrument part of the payload of SUNRISE, a stratospheric balloon mission in Antarctica. It is also the precursor of the Visible Imaging Magnetograph of the future ESA Solar Orbiter mission. It is essentially a diffraction‐limited imager that carries out spectropolarimetric measurements of high resolution (bandwidth of < 100 mÅ at 525.02 nm), and relates the polarimetric properties of the incoming light through a telescope with magnetic fields in the Sun, via the Zeeman effect. At the core of the instrument there are the polarization modulation components, two Liquid Crystal Variable Retarders (LCVRs). A demodulation efficiency is defined and used as the figure of merit, and it serves to find the theoretical optimum states for the LCVRs as well as to judge the quality of the pre‐flight calibration of the system. This calibration and the method used to optimize the actual efficiency is explained. Also, the space qualification of the LCVRs is presented, where ellipsometry played a major role in studying the effects of radiation, vacuum and temperature in the operation of the LCVRs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The IMaX polarimeter for the solar telescope SUNRISE of the NASA long duration balloon program

“…The scientific payload weighed around 1920kg and the total mass was 6.09 tons. The flight altitude typically was around 35-40km and, to achieve this, a balloon of approximately 130m of diameter with a volume of 835.000m 3 was utilized. The pressure at the flight altitude was 3-7mbar with the resulting difficulties in the high voltage handling (increase the risk of arc discharges), the heat transport mechanisms (only conduction and radiation, no convection) and the change of the focal plane position among others.…”

“…The polarization analysis is carried out using two Liquid Crystal Variable Retarders (LCVRs) and a polarizing beam splitter. Applying low voltages (<14V), four known polarization modulations were introduced and then, the four components of the Stokes vector were extracted [3]. The utilization of LCVRs in space instrumentation is very promising because it avoids rotary mechanisms (i.e.…”

Study of polarimeters based on liquid crystal panels

“…Nowadays, Liquid Crystal (LC) technology is commonly applied in the implementation of polarimeters [2,3,[7][8][9][10][11], leading to dynamic devices. Consequently, they present some advantages with respect to mechanical polarimeters [4,[12][13][14].…”

“…Polarization metrology is essential in many fields such as medical physics [1,2], astronomy [3] or material characterization [4]. Polarimeters are the basic instruments used to characterize the polarization state of a light beam or to determine the polarimetric properties of polarizing samples by means of radiometric measurements.…”

Arbitrary state of polarization with customized degree of polarization generator

“…In fact, experimental results are presented, providing an accurate control for the generation of SOPs (maximum error of 1.7% and 3.3% for ellipticity and azimuth, respectively) as well as for the associated degree of polarization (full experimental variation from 1 up to 0.003, with a 1.7% maximum error). The system proposed may be useful for different applications, for example, for polarimeters testing, speckle metrology, and biological applications.The accurate measure of light beam polarization or polarimetric samples is very important in a large number of applications [1][2][3][4][5][6][7][8][9]. In a number of those applications, the measure of the unpolarized content is very useful, as it may contain relevant information not present in the fully polarized content [10][11][12].…”