EPIC Medium-Scale
Optical Design
Huan Tran
Brad Johnson
Mark Dragovan
April 2009
EPIC-IM optical layout
EPIC-IM optical properties
•Crossed Dragone
•ABS, Clover, QUIXOTE, QUIET ….
•Unprecedented Large FOV
• 30x20 degrees
•Extreme Compact design
•Maximize resolution/throughput
in shroud
•Telecentric
•NO refractive elements
EPIC-IM optical properties
Oversize mirrors
“force” telecentric focal plane => cold aperture
EPIC-IM aberration performance
• Elliptical focal plane
– Limited by vignetting in Y
– Limited by aberration in X
• Multiband
– High Frequencies in center
– 30—800 GHz
• 11,000 bolometers
850 GHz
30 deg/ 160 cm
30 GHz
EPIC-IM cold vs warm
Main Beam Simulations
• Beam shapes
– No Refracting elements
– Calculated with Perfect Gaussian Feed horns
– Calculated for each “Hex”
• Polarized beam-scale distortions
– Fit Gaussians to beams
– Compare to benchmarks
PO co and cross–pol
beams for single feed
30 GHz beam, from Grasp 9
Spot diagram, from Zemax
PO vs GO sanity check
Main beam effects vs benchmark
EPIC-IM mirrors alone are below benchmarks w/o modulation
Sidelobes
• Analyzed with Physical Optics(PO) an
Geometric Theory of Diffraction (GTD)
• Aperture Integration Method
– Optics box
• Galaxy Convolution
EPIC-IM straylight
EPIC-IM farsidelobes
Co-pol beam, no baffling
~15d simulation time
Aperture Integration method
Set J =0 outside
Calculate Equiv J
28d sim time
Polarized Far Sidelobes
(QT2 + UT2 + VT2)1/2
2 x15d sim time
Galactic Contamination
•
In order to evaluate the effect of the signal from the far sidelobes, we convolve the qt
beam maps with a 150 GHz sky model.
•
The beam patterns have the primary beam masked, so only the response to the sidelobes are
evident in the output.
The sky data is an all sky map at long wavelengths (150 GHz).
Since the beam is asymmetric, it is necessary to rotate the beam with respect to the sky at
each point to get the complete convolution.
The convolutions were done using the totalconvolver code developed by the Planck
community. (Gorski et. al.)
•
•
•
M.Dragovan
(above)
The 150 GHz sky map with which the beams are convolved. Units are log(uK).
(below) The results of the convolution, qt beam with the above sky . Units are (uK).
M.Dragovan
In order to further quantify this result, we make two histograms: the number of pixels
with a given intensity (left plot), and the integrated histogram giving the total number of pixels
less than a given intensity (right plot). This is similar to the plots that are shown for site surveys.
Goal 1nK
By inspection one can see that fully 90% of the pixels are <0.2nK.
M.Dragovan
GTD and Polarization of sidelobes
•
Our Far sidelobe simulations were for 3.25 –f –l, but
Conclusions
• EPIC-IM has enormous throughput
• Systematic beam effects are below benchmark
• Sidelobes are manageable
– More analysis time required to be sure