The NIRCam instrument on the James Webb Space Telescope (JWST) will provide a coronagraphic
imaging capability to search for extrasolar planets in the 2 - 5 microns wavelength range. This capability is
realized by a set of Lyot pupil stops with patterns matching the occulting mask located in the JWST
intermediate focal plane in the NIRCam optical system. The complex patterns with transparent apertures
are made by photolithographic process using a metal coating in the opaque region. The optical density
needs to be high for the opaque region, and transmission needs to be high at the aperture. In addition, the
Lyot stop needs to operate under cryogenic conditions. We will report on the Lyot stop design, fabrication
and testing in this paper.
In 2009, we presented a compact division of amplitude imaging polarimeter design that captures the complete Stokes
parameters simultaneously. The advantages of this design are 1) reduced sensitivity to noise based on the optimized
selection of polarization elements, 2) minimization of differential aberrations in the four polarimetric channels, and 3)
reduction in image registration errors. A prototype polarimeter was integrated for the near-infrared wavelength, field
tested, and shown to calculate and display estimated scene polarization in real time. In this paper, several data sets are
presented showing the instruments unique remote detection capabilities from various platforms and scene types.
Acquisitions include ground view, aerial view of an urban area, and K-model rocket plume imaging at 2.5 kilometers.
The acquisitions were processed using several new polarimetric imaging techniques detailing the unique remote
detection capability. This polarimeter design was driven by the requirement to increase the accuracy of Stokes
estimation. Therefore, this paper will conclude with the precision or an estimate of errors associated with this particular
We have designed a new near-IR imaging polarimeter which generates the complete Stokes' vector estimation
simultaneously. The design is based on our first generation division of amplitude polarimeter where four images are
folded on to a single focal plane detector. This gives rise to a small compact rigid instrument. The design operation
wavelength is 632.8 nanometers. The new second generation design operates at a wavelength of 1550 nanometers and
has three improvements over the first generation: 1) the design of the Beam-Splitter Assembly (BSA) is based on an
optimization scheme where the Measurement (instrument) matrix is optimized for Stokes' vector estimation with noisy
data, 2) the four individual focusing lenses positioned after the BSA have been replaced by a single lens in front of the
BSA reducing differential image distortion, and 3) a reticle is placed at an intermediate image plane, providing a fiducial
mark in each of the images for precise registration.
We present the first high spatial resolution, passively-illuminated polarimetric images of boosting rocket exhaust
plumes. The images shown here show significant linear and circular polarization, and the ability to resolve
the polarization signals into images allows us to make some preliminary arguments as to their origins. Our
observations are consistent with polarization caused by Rayleigh and Mie scattering (linear) and interaction
with plume plasma-generated magnetic fields (circular). We also present nearly simultaneous, two-color, narrowband
(633 ± 5 and 750 ± 5 nm) exhaust plume images, where significant structural differences are observed in
the plumes despite a relative small difference in the two wavelengths.
We present the initial results of an imaging polarimeter operating at 632.8 nm that simultaneously analyzes four
polarization states on a single detector array. In a single snap shot, the polarimeter has the ability to characterize the
polarization of a scene by determining the complete Stokes vector. Images are processed to show Degree of Polarization
(DOP), Degree of Linear Polarization (DOLP), Degree of Circular Polarization (DOCP), ellipticity and the angle of
linear polarization. Our approach utilizes a monolithic analyzer that allows us to avoid issues usually associated with
division of amplitude polarimeters such as jitter and tight tolerance requirements. We discuss our optical design,
calibration procedure, and test data.
Simultaneous detection of the Stokes vector and Stokes images over a broad spectrum can be obtained from an achromatic division of amplitude imaging Stokes polarimeter. This is done through the use of a combination of beamsplitters, prisms and achromatic retarders to split the light into four different paths in collimated space and analyze each beam. Once each beam is focused onto the four quadrants of the camera, the Stokes vector, Stokes images and the degree of polarization across the scene can be obtained through the manipulation of the intensities for each image.