Post on 01-Apr-2015
Bolometric astronomical imaging at mm wavelengths
Stephen Yates
CNRS-CRTBT Grenoble - Astrophysique et matière noire groupe:
Alain Benoit, Philippe Camus, François-Xavier Désert and Samuel Leclercq.
Talk to European network on cryodetectors, 23/4/2004
1CNRS, Centre de Recherche sur les Très Basses Températures, 38042 CEDEX 9, Grenoble, France
Bolometers projects at the CRTBT
• Ground based bolometric camera observation at mm wavelengths
• Archeops: balloon based mm observation (2001/2)
• Planck: satellite space observation of cosmic microwave background (projected 2007)
• Edelweiss II, dark matter detection
Bolometric camera
• Ground based imaging
Current systems:• mainly 300mK, 100s of
individual bolometers (e.g. MAMBO, lower figure)
Our goal:• Bolometric camera @100mK
• Integrated bolometer array of up to 1000 pixels
Bolometer electronic Readout
• Capacitive current source
• Low temperature JFET
– Low noise measurements
• Modulated square wave excitation
– Reduces sensitivity to offset drift
– reduces amplifier 1/f and shifts to modulation frequency.
• Enables measurement of up to 30M
• Automated data acquisition and control
Triangle, generates square wave current through capacitor
Square wave reference
bolometer
Low temperature JFET, enables amplifier noise~0.5nV/Hz1/2
Multiplexing bolometer readout• For 1000 pixels, necessary to multiplex detectors
to reduce electronics/complexity
• Low temperature operation
• Successfully built and tested a multiplexer to read 8 bolometers
• Testing HEMT Quantum Point Contact transistor network (shown), made by Y.Jin (IPN) – Lower capacitance/dissipation
Vref
I
Vmeas
Transistor switches
Quantum behaviour of QPC transistor
Microfabricated bolometer arrays• Thin film bolometers, based on a thin
membrane, built and tested
• Characterisation using a low temperature black body source
• NbxSi1-x thermometer layer, fabricated at CSNSM Paris (L. Dumoulin)
Black body source and optics
Bolometer, 5x5mm, 100nm membrane
Bolometer arrays
• Array of 4 bolometers on chip
• Tested thermal conductivity of membrane and resistivity of thermometer.
Further work
• Expanding bolometer arrays,
• optimising fabrication of individual bolometers
• Antenna for bolometers (array shown)– Fourier spectrometer
• Expanding/testing multiplexing
• Optics for camera, filters for low temperature operation, refrigerator