11 research outputs found
Polarization Ray Tracing and Polarization Aberration Compensation in Reflective Astronomical Telescopes
Assessing and optimizing polarization performance in the context of ray-based optical design can be challenging. We describe an approach to this problem that decouples polarization effects from optical system geometry for reflective systems. Each surface's polarization properties are parameterized in terms of their impact on retardance and diattenuation in the small angle-of-incidence limit, separating polarization assessment from the task of coating design. A low-resolution ray trace of the system is adequate to determine ray geometry at each interface, which can then be interpolated to rapidly evaluate net Jones Matrix pupil functions. Coating behavior can be easily varied using the ellipsometric parameters to investigate impacts and compensation. Desired values of these parameters can then be specified as constraints in coating design. Investigation with candidate telescope optical designs for LUVOIR show baseline root-mean-square wavefront errors in the nm range for the on-diagonal Jones matrix component, and throughputs of tens of parts per million. Promising possibilities for compensation using a purpose-designed coating on the secondary mirror are discussed, which reduce the on-diagonal wavefront error by a factor 20, with accompanying but more modest reductions in coupling into off-diagonal terms
Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission
The New Horizons instrument named Ralph is a visible/near infrared
multi-spectral imager and a short wavelength infrared spectral imager. It is
one of the core instruments on New Horizons, NASA's first mission to the
Pluto/Charon system and the Kuiper Belt. Ralph combines panchromatic and color
imaging capabilities with IR imaging spectroscopy. Its primary purpose is to
map the surface geology and composition of these objects, but it will also be
used for atmospheric studies and to map the surface temperature. It is a
compact, low-mass (10.5 kg), power efficient (7.1 W peak), and robust
instrument with good sensitivity and excellent imaging characteristics. Other
than a door opened once in flight, it has no moving parts. These
characteristics and its high degree of redundancy make Ralph ideally suited to
this long-duration flyby reconnaissance mission.Comment: 18 pages, 15 figures, 4 tables; To appear in a special volume of
Space Science Reviews on the New Horizons missio
The James Webb Space Telescope Mission: Optical Telescope Element Design, Development, and Performance
The James Webb Space Telescope (JWST) is a large, infrared space telescope
that has recently started its science program which will enable breakthroughs
in astrophysics and planetary science. Notably, JWST will provide the very
first observations of the earliest luminous objects in the Universe and start a
new era of exoplanet atmospheric characterization. This transformative science
is enabled by a 6.6 m telescope that is passively cooled with a 5-layer
sunshield. The primary mirror is comprised of 18 controllable, low areal
density hexagonal segments, that were aligned and phased relative to each other
in orbit using innovative image-based wavefront sensing and control algorithms.
This revolutionary telescope took more than two decades to develop with a
widely distributed team across engineering disciplines. We present an overview
of the telescope requirements, architecture, development, superb on-orbit
performance, and lessons learned. JWST successfully demonstrates a segmented
aperture space telescope and establishes a path to building even larger space
telescopes.Comment: accepted by PASP for JWST Overview Special Issue; 34 pages, 25
figure
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
Recommended from our members
Snapshot spectropolarimetry
Channeled spectropolarimetry is a novel method of measuring the spectral dependence of the polarization state of light. Amplitude modulation is employed to encode all four Stokes component spectra into a single optical power spectrum. The encoding is performed with a simple arrangement of two thick birefringent retarders and a linear analyzer. No moving parts are required, and the system is able to acquire its data in a single detector array integration time. We report the results of an in-depth study of channeled spectropolarimetry. The mathematics of the amplitude modulation analogy are explored, providing a basic design procedure. The system's spectral resolution is described in terms of the space bandwidth product. The technique is then analyzed in the general context of linear operator theory, using both analytic and computational approaches to the singular value decomposition and pseudoinversion of the system's operator. This analysis highlights the importance of the choice of object space in constraining linear reconstructions of data from under-determined systems, and provides the underpinnings of the calibration and reconstruction techniques for a hardware prototype. Calibration of the prototype is approached as experimental estimation of the system's operator. Our basic method of reconstruction involves pseudoinversion of the operator while constraining object space to a truncated Fourier basis. Apodization is helpful in reducing the ringing of reconstructions of spectra which extend beyond the edges of the system's spectral range. Experimental results are presented, including comparisons between measurements taken with the channeled spectropolarimeter and a reference rotating compensator, fixed analyzer instrument. We have used measurements of the effects of stress birefringence on light propagated through material subject to time-varying stress to demonstrate time-resolved snapshot spectropolarimetry. Continuing efforts include the combination of channeled spectropolarimetry with computed tomography imaging spectrometry to realize a snapshot imaging spectropolarimeter