Thomas K. Hamilton

Snapshot imaging spectropolarimeter

We present and analyze a technique for snapshot imaging spectropolarimetry. The technique involves the combination of channeled spectropolarimetry with computed tomography imaging spectrometry (CTlS). Channeled spectropolarimetry uses sideband modulation to encode the spectral dependence of all four Stokes parameters in a single spectrum. CTIS is a snapshot imaging spectrometry method in which a computer-generated holographic disperser is employed to acquire dispersed images of the target scene, and both spatial and spectral information is reconstructed using the mathematics of computed tomography. The combination of these techniques provides the basis for a snapshot imaging complete Stokes spectropolarimeter that can be implemented with no moving parts. We review design considerations for the spectropolarimeter and present preliminary simulation results.

Stellar X-Ray Polarimeter: a focal plane polarimeter for the Spectrum X-Gamma mission

n this paper we describe an x-ray polarimeter that will be flown on the Spectrum X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and pho-toemission from a cesium iodide photocathode. These three methods allow polarization measurements over an energy band from 0.3 to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known x-ray sources, an increase of two orders of magnitude over the x-ray polarimeters flown to date. X-ray polarization measurements will allow us to constrain the geometry of gas flow in x-ray binaries, identify nonthermal emission in supernova remnants, test current models for x-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

Analysis of channeled spectropolarimetry using singular value decomposition

Channeled spectropolarimetry is a technique for measuring the spectral dependence of the polarization state of light. Passive polarization optics are used to encode the spectral dependence of the four Stokes components sk into a single irradiance spectrum. We treat the technique as a linear operator and compute its singular value decomposition numerically. The resulting singular functions divide into three distinct groups representing s0, s1 and mixtures of s2 and s3. The corresponding singular values indicate that measurements of the latter two groups will have signal-to-noise ratios reduced form that of s0 by factors of 0.6 and 0.4 respectively. The structure of the singular vectors is in agreement with a separate estimate of the systems resolution.

Midwave-infrared snapshot imaging spectrometer

We report results from a demonstration of a midwave-infrared non-scanning, high speed imaging spectrometer capable of simultaneously recording spatial and spectral data from a rapidly varying target scene. High speed spectral imaging was demonstrated by collecting spectral and spatial snapshots of blackbody targets and combustion products. The instrument is based on computed tomography concepts and operates in a mid-wave infrared band of 3.0 to 5.0 micrometers . Raw images were recorded at a frame rate of 60 fps using a 512 x 512 InSb focal plane array. Reconstructed object cube estimates were sampled at 46x46x21 (x, y,(lambda) ) elements, or 0.1 micrometers spectral sampling. Reconstructions of several objects are presented.

SXRP: an X-ray polarimeter for the SPECTRUM-X-Gamma mission

SummaryTheStellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several hundreds of known X-ray sources. X-ray polarization measurements will allow us to constrain the physical mechanisms and the geometries of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources.

MWIR computed tomographic imaging spectrometer experiments

We report results of experimentation with a new, high- resolution MWIR non-scanning, snapshot imaging spectrometer capable of simultaneously recording spatial and spectral data from a rapidly varying target scene. The instrument is based on computed tomography concepts and operates in a mid-wave infrared band of 3.0 to 5.0 micrometer. High speed spectral imaging was demonstrated by collecting spectro-spatial snapshots of an artificial target in the lab. Raw images were recorded using a 512 X 512 InSb focal plane array in snapshot mode.