Transcript 031031_St_Wkshop

The Prime Focus Imaging
Spectrograph – Old
Challenges and New Ones
K. Nordsieck, Principal Investigator
Jeff Percival, Eric Burgh, Michael Smith
Univ of Wisconsin
Ted Williams, Chuck Joseph
Rutgers University
Darragh O'Donoghue +
SAAO
• Old Challenges
– What kind of scientific observations?
– Big telescope  Big instrument optics
– Making good use of your observing time
• New Ones
– The SALT prime focus
– New optics: holography
Oct 30, 2003
PFIS - Student Wkshop
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Making a Powerful Astronomical
Instrument
High-Speed
Imager
• Efficiency
High-Speed
– Minimize loss in optics
Imaging
Spectrograph
– Extract maximum data
Spectroscopy: composition,
motion
Imaging
Polarimetry: structure,
Spectromagnetic field
polarimeter
– Observe many objects
simultaneously
• Resolution
– Spread out colors more
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PFIS - Student Wkshop
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Imaging Spectroscopy
Fabry-Perot etalons
(selects wavelength)
Filters
Perseus A in
Hydrogen Light
Perseus
Cluster of
Galaxies
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PFIS - Student Wkshop
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Multi-Object Grating Spectroscopy
Filters
VPH Grating
(Splits colors)
Up to 100 Spectra
Hubble
Deep
Field
(South)
Slitmasks
(selects objects)
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PFIS - Student Wkshop
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Optics Design Challenges
CCD
detector
300 nm 400
UV Blue
Camera
Grating
Collimator
Telescope Focus
Calcium Fluoride
Sodium Chloride (salt)
Calcium Fluoride
Fused Quartz
Fused Quartz
Fused Silica
Fused Silica
Sodium Chloride (salt)
Fused Silica
Calcium Fluoride
Calcium Fluoride
Fused Silica
Calcium Fluoride
Fused Silica
Calcium Fluoride
Fused Silica
500
600
700
800
Green Yellow
Red
Wavelength
PFIS range
900
Infrared
• For highest efficiency: use lenses
instead of mirrors
• Need many lenses to correct color
aberration  CAD
• Wavelength range: require crystals
to work into UV
• Lenses need to be very large (up to
25 cm)
• Assembled into large holders with
coupling fluid
Calcium Fluoride
Fused Quartz
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PFIS - Student Wkshop
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Collimator
Fused Quartz
CaF2
CaF2
Fused Quartz
Oct 30, 2003
Fused Quartz
(NaCl)
PFIS - Student Wkshop
Fused Silica
CaF2
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CaF2
Camera
(Fused Silica)
CaF2
Fused Silica
(Fused Silica)
CaF2
NaCl
Fused Silica
CaF2
(Fused Silica)
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PFIS - Student Wkshop
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Multi-object Spectroscopy with custom masks
at focus of telescope:
• Laser-cut slit masks
• Unique mask cut for each
individual observation
• Slit mask magazine will hold 30
multi-object slit masks
• Reload once/ week
Oct 30, 2003
Giant
Elliptical
Galaxy
NGC1399
PFIS - Student Wkshop
Mask with slits
cut in it to let
through selected
nebulae in galaxy
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New Challenges: on SALT
Prime Focus
Spectrograph
Prime Focus
Tracker
Motion of tracker and illumination of primary mirror as an object sets
The instrument must be:
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PFIS - Student Wkshop
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Small and Lightweight
Open space frame
welded from hollow
square tubes of invar
(low- expansion
stainless steel)
DEIMOS on Keck
3x4m, 9000 kg
Oct 30, 2003
PFIS on SALT
1.5x2m, 500 kg
PFIS - Student Wkshop
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Stiff
CAD 3D model of
PFIS structure
Perpendicular to Dispersion
Spec
microns/ track
20
10
Parallel to Dispersion
0
-80
-60
microns/ track
20
-40
-20
0
20
Declination (deg)
Spec
10
0
-80
-60
-40
-20
0
Declination (deg)
FEA ("Finite Element
Analysis") showing how
it bends under gravity
Oct 30, 2003
PFIS - Student Wkshop
Plus model of
how tracker
moves and PFIS
optics shows how
image moves
during exposure 11
20
Remote control
Grating
Jukebox
Etalon Insertors
Slitmask
Jukebox
Filter
Jukebox
Shutter
Camera
Waveplate
Rotator
Articulation
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PFIS - Student Wkshop
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Compact
New technology:
• Grating "grooves"
formed by hologram
• Interference pattern
from two laser
beams on gelatin
film
• Efficient, large,
inexpensive custom
gratings
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PFIS - Student Wkshop
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Astronomical Instrumentation is a exciting business.
A big demand for:
Astronomers
Physicists
Optical Engineers
Mechanical Engineers
Software Engineers
...........
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PFIS - Student Wkshop
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