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
320
280
Etendue (m2 deg2)
240
200
160
120
80
40
0
LSST
PS4
PS1
Subaru
CFHT
SDSS
MMT
DES
4m
VST
VISTA
IR
SNAP
Opt+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
17.5
Filter
u
g
r
i
z
Y
23°
Radius of spot in microns
17
16.5
Radial component
19°
16
14°
15.5
Angle in
degrees
0
14
14
19
19
23
23
23°
Azimuthal component
19°
14°
15
0°
14.5
0.000
0.200
0.400
0.600
wavelength in microns
0.800
1.000
1.200
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
19
Spot radius in microns
18.5
18
Distance from
center in mm
17.5
0
50
100
150
200
250
300
317
17
16.5
16
15.5
15
14.5
0.000
0.200
0.400
0.600
Wavelength in microns
0.800
1.000
1.200
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
19
Spot radius in microns
18.5
18
Distance from
center in mm
17.5
0
50
100
150
200
250
300
317
17
16.5
16
15.5
15
14.5
0.000
0.200
0.400
0.600
Wavelength in microns
0.800
1.000
1.200
0.384 micron wavelength Gaussian beam at an angle
180
160
140
Angle in
degrees
Spot radius in microns
120
0
14
19
23.6
14
19
23.6
100
80
60
Azimuthal
Radial
40
20
0
-400
-300
-200
-100
0
100
Distance from center of focal plane in mm
200
300
400
0.994 micron wavelength Gaussian beam at an angle
500
450
400
Angle in
degrees
Radius of spot in microns
350
0
14
14
19
19
23.6
23.6
300
250
200
150
Azimuthal
Radial
100
50
0
-400
-300
-200
-100
0
100
Distance from center of focal plane in mm
200
300
400
Testing Schematic
Reference
Photodiode
Photodiode
Laser
Array
30 micron spot
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
Optical Flat
Precision
movable
platform
Laser
displacement
sensors
Optical Flat
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://navj.wz.cz/061116_025307-70_56_19_226.jpg
http://www.cambridgeincolour.com/tutorials/graphics/airydisk-3D.png
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).