Calibration of the LSST Camera
Andy Scacco
LSST Basics
• Ground based
• 8.4m triple mirror design
• Mountaintop in N. Chile
• Wide 3.5 degree field survey telescope
• ~30 Tbits / night of data
• Dark energy / cosmology
LSST Layout
Etendue
• Etendue = FOV * Collecting area• Measures the rate of incoming data
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Ete
nd
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eg2 )
LSST PS4 PS1 Subaru CFHT SDSS MMT DES 4m VST VISTAIR
SNAPOpt+IR
The point spread function
• Stars are point sources
• PSF is image of a point source
• Combination of atmosphere + telescope aberration
• Measured by the full width at half maximum (FWHM)
• PSF of LSST has a
30 micron FWHM
Atmospheric Seeing
• Atmosphere blurs images
• Instrumental blurring is much less than atmosphere
• Large ground based telescopes need adaptive optics
Camera Design
Focal Plane CCD Array
• We need a 30 micron spot on focal plane
• CCD wells are 10 x 10 microns
• LSST has 3.2 Gpixels
Laser
• TEM00 mode
• Helium-neon / Tunable
• Gaussian beam
• Very good for optics analysis
Monochromator part 1
• Filter / Monochromator
• Pinhole produces Frauenhofer diffraction
• Airy diffraction pattern
Monochromator part 2
• Airy pattern resembles Gaussian
• Second pinhole cuts off all but the central peak
Lens aberrations
• Lenses aren’t perfect
• Astigmatism
is biggest
problem for us
Astigmatism
• Sagittal / tangential rays focus to different locations
Camera ZEMAX Design
Spot size as a function of wavelength for a Gaussian beam with an initial waist radius of 15 microns striking the center of the focal plane at an angle
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wavelength in microns
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t in
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ron
s
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Azimuthal component
Radial component
Angle in degrees
23°
19°
14°
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0°
u g r i z YFilter
Radial spot size as a function of wavelength for a 15 micron radial waist Gaussian beam pointed at a 0 degree angle from varying distances from the center of the focal plane
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Wavelength in microns
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ot
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in m
icro
ns 0
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317
Distance from center in mm
Radial spot size as a function of wavelength for a 15 micron radial waist Gaussian beam pointed at a 0 degree angle from varying distances from the center of the focal plane
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Wavelength in microns
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ot
rad
ius
in m
icro
ns 0
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317
Distance from center in mm
0.384 micron wavelength Gaussian beam at an angle
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Distance from center of focal plane in mm
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ot
rad
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in m
icro
ns
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Angle in degrees
AzimuthalRadial
0.994 micron wavelength Gaussian beam at an angle
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Distance from center of focal plane in mm
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diu
s o
f s
po
t in
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ron
s
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23.6
23.6
Angle in degrees
AzimuthalRadial
Testing Schematic
Reference
Photodiode Laser
30 micron spot
Photodiode
Array
Focal Plane
My Other Project…
• Testing a laser sensor system for use in measuring distance very precisely
• It will be accurate enough to be used to measure the flatness of the focal plane of the LSST
Apparatus
Laser displacement sensors
Optical Flat
Optical FlatPrecision movable platform
Data
Data #2
Further work
• Figure out why the correction function differs between the two trials
• Calculate a best fit sawtooth function to subtract from the data to make it more accurate
• Use the sensor with the correction function to measure the components of the LSST
Acknowledgements
• David Burke – my excellent mentor
• Andy Rasmussen – other excellent mentor
• Steve Rock
• The DOE, Office of Science
• SLAC
• Stanford
• All my fellow SLAC-ers
References
http://www.cambridgeincolour.com/tutorials/graphics/airydisk-3D.png
http://navj.wz.cz/061116_025307-70_56_19_226.jpg
http://www.rp-photonics.com/img/gauss_r.png
http://publication.lal.in2p3.fr/2001/web/img344.gif
http://laser.physics.sunysb.edu/~wise/wise187/2005/reports/deb/gauss1.gif
http://cache.eb.com/eb/image?id=3246&rendTypeId=4
References 2• “Large Synoptic Survey Telescope”, Available at http://www.lsst.org
(2007 August 9).• D. Burke, private communication (2007).• “Point Spread Function”, Available at http://en.wikipedia.org (2007 August
6).• “Astronomical Seeing”, Available at http://en.wikipedia.org (2007 August 3).• “Full Width at Half Maximum”, Available at
http://www.noao.edu/image_gallery/text/fwhm.html (2007 August 6).• “Gaussian Beam”, Available at http://en.wikipedia.org (2007 July 25).• A. Sonnenfeld, private communication (2007). • “Airy Disk”, Available at http://scienceworld.wolfram.com/physics/ (2007 July
25).• “Astigmatism”, Available at http://en.wikipedia.org/wiki/Astigmatism (2007
July 25).• “Aberrations”, Available at http://grus.berkeley.edu/~jrg/Aberrations/ (2007
July 25).