摘要: The science of measuring the polarization state of light is called polarimetry. There are two type of polarmeters: (1) those that actively irradiate an object with light of known polarization and (2) those that passively record ra... 展开 The science of measuring the polarization state of light is called polarimetry. There are two type of polarmeters: (1) those that actively irradiate an object with light of known polarization and (2) those that passively record radiation emitted and/or reflected by objects. Polarimeters in the thermal infrared (midwave infrared (MWIR)) are just becoming available, and accuracy and calibration issues are yet to be determined experimentally. The polarization effects of the instrument that measures light must be fully known, as well as the intervening atmosphere or media. In each case, a Mueller matrix can be used to describe instrumental and other effects. In addition, the polarimeter must be able to determine all Stokes parameters of the radiation at the instrument's entrance pupil. Such a polarimeter is known as a 'complete' polarimeter. The subject of this report is the construction and experiments with a complete imaging polarimeter. Stokes parameters can be used to describe light that is partially polarized. The first Stokes parameter, typically labeled So, represents the total irradiance recorded from an instantaneous field of view. The second Stokes parameter, S1, represents the preference of the collected radiation for horizontal versus vertical polarization. A positive value of S1 indicate horizontal polarization. The third Stokes parameter, S2, represents the preference of the collected radiation for linear polarization oriented along 45degrees and 135degrees measured with respect to the horizontal direction. A positive value of S2 indicates 45degree linear polarization. The fourth Stokes parameter, S3 indicates right-circular polarization. Polarimeters can be also divided into two classes: (1) time-sequential or (2) snapshot. The time-sequential polarimeter measures Stokes parameters by employing one or more rotating polarization elements. A snapshot polarimeter measures Stokes parameters by aperture of amplitude division. All parameters are measured simultaneously. In this report, we describe a time-sequential imaging polarimeter that employs a rotating form-birefringent retarder element. The extension of polarimetry from the visible to the MWIR and long-wave infrared (LWIR) has been limited by the lack of IR polarizers and retarders. Also, in analogy to spectral imaging, the relatively recent availability of large-format MWIR imaging arrays is enabling an exploration of polarization's value in target and anomaly detection. 收起