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Readme file for off-axis PSF files for WFIRST coronagraph design SPC-20181220.
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Author: A.J. Riggs (Jet Propulsion Laboratory, California Institute of Technology)
Copyright 2019 California Institute of Technology. Government sponsorship acknowledged.
The decision to implement the WFIRST mission will not be finalized until NASA’s completion of the National Environmental Policy Act (NEPA) process. This document is being made available for information purposes only.
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The package is to provide realistic morphologies of the Shaped Pupil Coronagraph (SPC) Wide Field of View (FOV) PSF profile for science modeling purposes.
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This file package contains :
readme_SPC-20181220_offaxis.txt (this file)
cube_PSF_SPC20181220_1D_x-axis_0to11by0.1.fits
cube_PSF_SPC20181220_1D_x-axis_14.5to25.5by0.1.fits
cube_PSF_SPC20181220_2D_0to10by0.5.fits
cube_PSF_SPC20181220_2D_0to25by1.fits
xy_offsets_SPC20181220_2D_0to10by0.5.fits
xy_offsets_SPC20181220_2D_0to25by1.fits
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General information about the PSF generation:
SPC wide-FOV imaging mode design, SPC-20181220, by A.J. Riggs
for CGI's Band 4, 825nm @ 10% bandwidth),
uses the (early) Phase B pupil named CGI-180718.
The three diffractive coronagraph masks included in the optical model are
1) a shaped pupil apodizer,
2) an annular-opening focal plane mask (FPM), and
3) a Lyot stop.
By design, the FPM has a required diffractive outer iris/diaphragm at 20 lambda_central/D, which limits the useful field of view to a 20 lambda_central/D radius.
- I use the term “focal plane mask” (FPM) to mean a diffractive mask playing an active role in diffractive starlight suppression. The SPC's FPM is NOT a field stop--a field stop has no diffractive effect and is used only to prevent the detector from saturating. The outer opaque iris part of the SPC’s FPM is essential to the SP(L)C's ability to create high contrast, just as much so as the inner occulting spot, and so it cannot be removed or treated separately. That means that we can never see the core of a point source more than 20 lambda_central/D away from the targeted star with the SPC-WFOV coronagraph.
- The dark hole (DH) region of the stellar PSF is an annulus from 5.4 to 20 lambda_central/D, which matches the opening region of the annular FPM upstream.
- Telescope diameter D = 2.3631 m
- The DICAM plate scale is 2 pixels per lambda_central/D, for lambda0=500nm (~22mas/px).
- These are 10% bandwidth images composed of PSFs summed over 11 evenly-spaced, summed wavelengths.
- Energy is normalized such that the input WFIRST pupil (with struts and secondary mirror obscurations included) has a total energy of 1.
- Total intensity over all pixels at each subsequent optical plane would therefore also equal 1 if the coronagraph masks were removed from the model.
The optical model used...
Accounts for:
- Geometric obscuration of the WFIRST pupil
- Core throughput losses due to diffraction from WFIRST pupil
- Core throughput losses due to coronagraph masks.
Does not account for:
- detector effective QE
- Model Uncertainty Factors (i.e., MUF=1)
- Reflection losses in the telescope optics
- Reflection and transmission losses inside CGI (exclusive of coronagraph masks)
- Optical aberrations, jitter, or wavefront correction
- (These are less important to model than for the other coronagraph modes because the inner working angle (IWA) is so large. The large IWA makes the coronagraph more robust against those aberrations.)
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Details on the SPC-WFOV coarse 2D-grid and finer 1D-grid PSF cubes.
True for all PSF datacubes:
-2D PSFs are 202x202 pixels in size
-5 pixels per lambda_central/D
-pixel-centered arrays (same origin convention as used by FFTs)
-The vector of x- or y-axes pixel coordinates in units of lambda_central/D are therefore computed as:
N = 202.
res = 5.
x = (-N/2.:(N/2.-1.))/res
y = x
Data in cube_PSF_SPC20181220_1D_x-axis_0to11by0.1.fits file:
-for capturing effects of off-axis PSF peaking out from behind the inner opaque spot of the focal plane mask.
-1D grid of offsets along x-axis
-source offsets along x-axis only, from 0 to 11 lambda_central/D in steps of 0.1 lambda_central/D
-datacube of 121 PSFs
Data in cube_PSF_SPC20181220_1D_x-axis_14.5to25.5by0.1.fits
-for capturing effects of off-axis PSF peaking out from behind the outer opaque iris part of the focal plane mask.-1D grid of offsets along x-axis
-source offsets along x-axis only, from 14.5 to 25.5 lambda_central/D in steps of 0.1 lambda_central/D
-datacube of 121 PSFs
Data in cube_PSF_SPC20181220_2D_0to25by1.fits file:
-Complete 2D grid of offsets along x- and y-axes, with (x,y) offset coordinates for datacube slices given in the file:
- xy_offsets_SPC20181220_2D_0to25by1.fits
-source offsets along x- and y-axes, from 0 to 25 (inclusive) lambda_central/D in steps of 1.0 lambda_central/D
-datacube of 26x26=676 PSFs
Data in cube_PSF_SPC20181220_2D_0to10by0.5.fits file:
-Inner 2D grid of offsets along x- and y-axes, with (x,y) offset coordinates for datacube slices given in the file:
- xy_offsets_SPC20181220_2D_0to10by0.5.fits
-source offsets along x- and y-axes, from 0 to 10 (inclusive) lambda_central/D in steps of 0.5 lambda_central/D
-datacube of 21x21=441 PSFs
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* More details about the optimization method of this SPC design can be found in :
1) A. Riggs, et al., "Shaped pupil coronagraph design improvements for the WFIRST Coronagraph Instrument", Proc. SPIE, 10400 (2017)
2) N. Zimmerman, et al., "Shaped pupil Lyot coronagraphs: high-contrast solutions for restricted focal planes," JATIS, 2, 1 (2016)
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This document was generated on:
1st draft on 2018-12-18 by A.J. Riggs
Modified on 2018-12-19 by A.J. Riggs
Modified on 2019-01-03 by A.J. Riggs to be for design SPC-20181220.
Contact aj.riggs@jpl.caltech.edu for any questions or suggestions.
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