SCUBA-2 Imaging Fourier
Transform Spectrometer
David A. Naylor and Brad G. Gom
University of Lethbridge, Canada
On behalf of the Canadian SCUBA-2 Consortium
SCUBA-2
The new Submillimetre Common User Bolometer Array camera for the JCMT
Key Features:
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Simultaneous imaging at 450 and 850 μm
Large 8 x 8 arc minute field of view
~10000 pixels, 0.5fλ spacing
Sky background limited performance
Novel scanning modes to provide large scale
surveys
Will have both imaging spectroscopic and
polarimetric capabilities
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 TES Detectors
Detector
chip
Micro-machined
silicon walls
0.5F = 1.135mm at 850m
Silicon walls
(50m)
Wire-bond
pads
Degenerately
doped layer
Multiplexer
chip
10m gap
Silicon
quarterwave delay
Silicon wafer
(60m)
Bump bonds
(2 per pixel)
MoCu bilayer
TES
Heater
Doped
layer
absorber
SiN membrane
(0.5m)
Resistance
RN
I
SQUID
Amplifier
RC
Bias point
V bias
R(T)
Tc
TES
Temperature
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 on the JCMT
Tertiary mirror
(f/12)
Elevation bearing
(f/7 field image)
Mirror N1
Cabin
optics
Nasmyth
Platform
Detectors
(f/2.7)
Window
Cryostat
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 Feed Optics
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 Field of View
JCMT/SCUBA-2
(450m)
7 arcsec resolution : 64 arcmin2 field-of-view
(simulation by Governato et al.)
Herschel/SPIRE
(350m)
25 arcsec : 16 arcmin2
(simulation by Hughes
& Gaztanaga)
JCMT/SCUBA
(850m)
14 arcsec : 5 arcmin2
(HDF image from Hughes
et al. 1998)
Compact ALMA
(450m)
0.01 arcsec : 0.02 arcmin2
•~1000x faster mapping than SCUBA
•Pathfinder instrument for high resolution telescopes such as ALMA
•To reveal the underlying chemistry, we need spectral information at each pixel
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
•0.005 cm-1 resolution
•Continuum is preserved
Naylor, D.A., Gom, B.G., Schofield, I., Tompkins, G., Davis, G.R., “Mach-Zehnder Fourier transform spectrometer for astronomical
spectroscopy at submillimeter wavelengths”, Proc. SPIE, Millimeter and Submillimeter Detectors for Astronomy 4855, 540-551 (2003).
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 FTS Science Goals
the FTS fills a niche between the SCUBA-2 continuum images and the higher
spectral resolution, but limited size images, provided by heterodyne array receivers
(e.g. HARP).
Interstellar Medium - offers both a rich spectrum, with continuum and
line components, and a rich field. The IFTS will allow for the spectral
index mapping of molecular clouds and in particular identify those
sources where a significant contribution to the total band flux arises from
line emission.
Ultra-Luminous Infra-Red Galaxies (ULIRGs) – measure the
Spectral Energy Distribution (SED) of the dust emission from ULIRGs.
Planetary atmospheres - inventory molecular species and provide
information on the physical and dynamical processes of the atmospheres
(e.g. internal heat sources). Spectral mapping of the Jovian, Saturnian
and Martian discs to study hemispheric, zonal and polar differences and
transport effects.
Super novae remnants - large scale mapping of super nova remnants
and interaction with the interstellar medium.
High red shift objects - initial estimates indicate that it may be
possible to determine the red shift through careful measurements of the
slope of the continuum across the 850 µm band.
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 FTS Features
Hyperspectral mapping - Combining the increased sensitivity of
SCUBA-2 with the resolution of the FTS, will provide an unprecedented
hyperspectral imaging ability in the submillimetre.
Mach-Zehnder Design - This innovative FTS design provides high
efficiency and access to all four ports of the interferometer. With this
design, both ports could view the sky, or one could view a cold load.
Dual wavelength operation - The SCUBA-2 FTS will take advantage of
the unique simultaneous dual wavelength capability of the SCUBA-2
system.
Variable spectral resolution - The resolving power of the FTS can be
selected instantly within a range of 10 to 5000.
Novel observing modes - The instantaneous, fully-sampled image
plane in SCUBA-2 will provide better image fidelity. The potential exists
for exploiting the DREAM observing mode to provide atmospheric
correction for each frame in the interferogram.
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Mach-Zehnder FTS Instrument Concept
•Access to all 4 ports
•Factor of 4 optical path multiplication
•Requires matched 50% beam splitters
Ade, P.A.R, Hamilton, P.A., and Naylor, D.A., “An Absolute Dual Beam Emission Spectrometer”,
Optical Society of America, FTS topical meeting, poster FWE3, Santa Barbara, California, June
1999.
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Intensity Beam Dividers
•4RT efficiency > 90%
•Factor of 4 frequency range
•2 metal meshes in an FP configuration
•Allows HeNe laser alignment
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
FTS operating modes
SCUBA-2 frame rate is fixed at 200 Hz
Continuous scan mode
•Table scanned at constant velocity
•Frames read out at 200 Hz
•Requires a non-uniform FT
•Low res. scans in ~1 sec
•High res. scans in ~30 sec
•Dual inputs on the sky for nulling operation
Step-and-integrate mode
•Table moved in discrete intervals
•Requires double modulation of the signal for sky correction
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
SCUBA-2 DREAM Mode
•DC biased detectors – sky background variations are
much larger than the signal
•SMU moves through a jiggle pattern, so that each sky
position is sampled by many bolometers
•transform raw bolometer data into partially calibrated
data on a regular spaced grid, thereby correcting for
the effects of:
•The impulse response of the electronics.
•The motion of the SMU.
•Differences between bolometers (Piston
correction)
•The Earth's atmospheric emission.
•Distortions in the bolometer positions.
•Corrected images are produced at ~1 Hz
•High res. step and integrate scans would take ~1.5
hours!
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Intentional ‘Aliasing’
DC band limited Nyquist sampling:
Shannon theorem for band limited signals:
If the detector is truly band limited, then we can use
the Shannon theorem to reduce the number of
samples in the interferogram
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Nyquist = 160cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Nyquist = 40cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Nyquist = 20cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Nyquist = 10cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Nyquist = 5cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Normal DC band limited Nyquist = 25 cm-1
‘Aliasing’ mode Nyquist = 5 cm-1
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Expected Performance
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003
Project Milestones
Conceptual Design Review
July 2003
Preliminary Design Review
May 2004
Critical Design Review
October 2004
Complete instrument tests
October 2005
Delivery to telescope
March 2006
“SCUBA-2 Imaging Fourier Transform Spectrometer” SPIE San Diego Annual Meeting #48 [5159-10] August 6, 2003