Report

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: 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 850m Silicon walls (50m) Wire-bond pads Degenerately doped layer Multiplexer chip 10m gap Silicon quarterwave delay Silicon wafer (60m) Bump bonds (2 per pixel) MoCu bilayer TES Heater Doped layer absorber SiN membrane (0.5m) 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 (450m) 7 arcsec resolution : 64 arcmin2 field-of-view (simulation by Governato et al.) Herschel/SPIRE (350m) 25 arcsec : 16 arcmin2 (simulation by Hughes & Gaztanaga) JCMT/SCUBA (850m) 14 arcsec : 5 arcmin2 (HDF image from Hughes et al. 1998) Compact ALMA (450m) 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