View
215
Download
1
Tags:
Embed Size (px)
Citation preview
wnb060905 BDT-I 2
Detector
• More than ‘sensing device’
• Measuring– ‘Meten is weten’
• Meta information• Counting vs analog
Nrms
wnb060905 BDT-I 5
Accuracy
• Distribution: stochastic measurement process only
• ==Precision
• Accuracy -> no systematic– Hubble– Target shooting
wnb060905 BDT-I 6
Statistics
• Mean• Variance• Chi-squared• Median
n i
n i
n i
xsquaredchi
xxn
var
xn
xmean
22
22 var)(sample 1
1
wnb060905 BDT-I 8
Systematic errors
• Instrument environment widest sense– Coal – Parallax– Gaia
• Gal rotation• Pressure
• Model -> none
• Outliers
wnb060905 BDT-I 10
(In)direct
• Direct– Raindrops– Planet directly
• Indirect– Crop size– ‘systematic’ movement of Centre of G.
• ‘Test particle’
wnb060905 BDT-I 11
Measurables
• EM waves
• Neutrinos
• Matter (nuclei -> meteorites & space craft)
• Gravitational waves (<=c)
wnb060905 BDT-I 12
Neutrinos
e
e
enp
epn
Weak interaction: electron
neutrinos
Strong interactionTau & muon
neutrinos
wnb060905 BDT-I 13
Neutrinos 2
• Long pathlength -> memory
• 1931: Pauli – 1959: e – 1962: new muon
• Indirect
• Icecube
• Ocean
• Moon
wnb060905 BDT-I 14
Neutrino 3
• Solar problem
• 1987 SN -> 19 neutrinos (water, proton decay)
• 50000 tons; 11000 PMT (50cm)
• Mass < 2.2eV
wnb060905 BDT-I 16
GW
• 10-38 weaker than EM force
• Transparant universe• Tensor (cf vector and
potential)• Helicity +-2 (+-1)
wnb060905 BDT-I 17
GW 2• Direct resonant
– Block > 1 ton Al; eigen freq. 1.5Hz– Coincident
• Direct non-resident– Michelson between 2 blocks (multiple reflections)
• Interferometer• LISA, in 2015 5Gm long 3.• Indirect: (but questioned again)
– dP/dt decay in binary pulsar.– Calculated: -2.403(0.002) 10-12 ss-1
– Observed -2.4 (0.09) 10-12 ss-1
wnb060905 BDT-I 18
Matter
• Cosmic Rays (later lecture)– Pierre Auger (AR) + Northern– LOFAR
• Meteorites -> history
• Returning spacecraft
wnb060905 BDT-I 19
EM radiation
• Energy == wavelength == frequency• Flux• Time variation • Spatial dependence• Polarisation:
– Only ‘directional’ measurement (magnetic field)
• Resolution in all:– Uncertainty – ‘aperture’
wnb060905 BDT-I 22
• 21 cm = 1420 MHz [Hyperfine line, HI]• 1 cm = 30 GHz• 1 mm = 300 GHz = 1000μm• 1 μm = 1000 nm• 550 nm = 5.5 × 1014 Hz [V band centre]• 1 eV = 1.60 × 10−12 erg = 1240 nm• 13.6 eV = 91.2 nm [Lyman limit = IP of HI]• 1 keV = 1.24 nm = 2.4 × 1017 Hz• 1 PHz = 1015 Hz (petahertz)• mec2 = 511 keV
wnb060905 BDT-I 23
Sensitivity
Faintest UVOIR point source detected:
• Naked eye: 5-6 mag
• Galileo telescope (1610): 8-9 mag
• Palomar 5-m (1948): 21-22 mag (pg),
• 25-26 mag (CCD)
• Keck 10-m (1992): 27-28 mag
• HST (2.4-m in space, 1990): 29-30 mag
wnb060905 BDT-I 24
MeasureFlux is the energy incident per unit time per unit areawithin a defined EM band:f ≡ Ein band/A t(or power per unit area)Usually quoted at top of Earth’s atmosphere
o “Bolometric”: all frequencieso Finite bands (typically 1-20%) defined by, e.g., filters suchas U,B,V,Ko “Monochromatic”: infinitesimal band, ν → ν + dνAlso called “spectral flux density”Denoted: fν or fλ
Note conversion: since fνdν = fλdλ and ν = c/λ,→ νfν = λfλ
wnb060905 BDT-I 25
Flux 21 Jy = 10−26 W m−2 Hz−1
[= 10−23 erg s−1 cm−2 Hz−1] non SI
Monochromatic Apparent Magnitudeso mλ ≡ −2.5 log10 fλ − 21.1,where fλ is in units of erg s−1 cm−2 A−1
o Normalization is chosen to coincide with the zero point of the widely-used “visual” or standard “broad-band” V magnitude system:i.e. mλ(5500 ˚A) = Vo Zero Point: fluxes at 5500 ˚A corresponding to mλ(5500˚A) = 0, are (Bessell 1998)f0
ν = 3630 Jy (janskys) or 3.63 × 10−20 erg s−1 cm−2 Hz−1
λ/hν = 1005 photons cm−2 s−1 A−1 is the corresponding photon rate per unit wavelength
wnb060905 BDT-I 26
Flux 3
• Absolute Magnitudes o M ≡ m− 5 log10(D/10), where D is the distance to the source in parsec o M is the apparent magnitude the source would have if it were placed at a distance of 10 pc. o M is an intrinsic property of a source o For the Sun, MV = 4.83
wnb060905 BDT-I 27
Flux 4
• Luminosity L (W)– Power (energy/s) radiated by source into
4π sterad
• Flux (W m-2)– f = L/4πD2 if source isotropic, no
absorption
• Brightness I (W m-2 sr-1)– f ~ IΔΩ
wnb060905 BDT-I 29
Planck 2
• Limiting forms:
• hν/kT << 1 → Bν(T) = 2kT /λ2 (“Rayleigh-Jeans”)
• hν/kT >> 1 → Bν(T) = 2hν3 e−hν/kT /c2 (“Wien”)
• Non-thermal– T > 1020
B
wnb060905 BDT-I 33
QEEye 10-20%
Photographic 2-10%
CCD 70-90%
PMT 20-30%
IR (HgCdTe) 30-50%
CMOS 60-80%
wnb060905 BDT-I 36
DetectorsBolometers
• Most basic detector type: a simple absorber
• Temperature responds to total EM energy deposited by all mechanisms during thermal time-scale
• Electrical properties change with temperature
• Broad-band (unselective); slow response
• Primarily far infrared, sub-millimetre (but also high energy thermal pulse detectors)
wnb060905 BDT-I 38
Detectors 2Coherent Detectors
Multiparticle detection of electric field amplitude of incidentEM wave• Phase information preserved• Frequency band generally narrow but tuneable• Heterodyne technique mixes incident wave with localoscillator• Response proportional to instantaneous power collected inband• Primarily radio, millimetre wave, but some IR systems withlaser LOs
wnb060905 BDT-I 39
Detectors 3
Photon Detectors• Respond to individual photon interaction with
electron(s)• Phase not preserved• Broad-band above threshold frequency• Instantaneous response proportional to
collected photon rate (not energy deposition)• Many devices are integrating (store
photoelectrons prior to readout stage)•
wnb060905 BDT-I 40
Detector 4
UVOIR, X-ray, Gamma-rayo Photo excitation devices: photon absorption changesdistribution of electrons over states. E.g.: CCDs,photographyo Photoemission devices: photon absorption causesejection of photoelectron. E.g.: photocathodes anddynodes in photomultiplier tubes.o High energy cascade devices: X- or gamma-rayionization, Compton scattering, pair-production
produces multiparticle pulse. E.g. gas proportional counters, scintillators
wnb060905 BDT-I 42
Eye
• Rods (10-20%)
• Cones (1-2%) – 3 varieties
• 1ps response; 1/20s integration; 15min to revitalise
• Flashes
wnb060905 BDT-I 43
Photographic
• - non-linear
• - low dynamic range
• + # pixels
• Photon excites e AgCl -> +Ag- into Ag.(defect)
• Developing == amplification
• Slow (but stroboscopic)
wnb060905 BDT-I 48
MCP2
• QE 20%
• Can be staggered (chevron)
• Up to million amplification
• 1-1000nm
wnb060905 BDT-I 49
IPCS
• TV: photo electron (from Si) stored in micro-capacitors
• Scanned/recharged 25Hz -> discharge current
• High readout noise (snow)
• 1st intensifier 3 stage million gain
• Read out == photon counting digital
wnb060905 BDT-I 55
CCD
• Workhorse up to 1.1 um -> bandgap• Dynamic range: bits; 30000:1• Linearity: same• Read-out noise 2-3 e-
• Dark current (thermal) -> cool• Shot noise: random photons• Non-uniformity -> flat fielding• Charge transfer efficiency (>.99999 has to be)• Cosmic rays: pixel error
wnb060905 BDT-I 56
CCD2
• Large: 10.5 * 10.5 kpixel
• 4 stitched -> 500 million pixels
• Thinned back-illuminated: no reflection
• Thinned very expensive: fragile, but efficient
wnb060905 BDT-I 57
CCD perfect?
CosmicraysHot Spots(high darkcurrent,butsometimesLEDs!)BrightColumn(charge traps)
DarkColumns
(chargetraps)
QEvariations
wnb060905 BDT-I 58
CMOS
• Complementary Metal Oxide Silicon
• Direct readout
• But: 15-30 photomasks; rather than 10 for CCD
wnb060905 BDT-I 61
NIR
• Similar to CCD
• Non-Si layer to generate photo electrons: HgCdTe and InSb for between 0.9 and 25 um
• Hybrid Si system: well developed
• Cooled to 30-60K
• Si part: CCD or MOS capacitors: direct read-out
•Pixel cost 10* CCD (0.10-0.30 USD)
wnb060905 BDT-I 62
SIS – BIB - SSPM
• Superconductor-Insulator-Superconductor tunnel junctions
• Blocked-Impurity-Band detectors
• Solid-State-PhotoMultipliers
• Josephson junctions
wnb060905 BDT-I 64
STJ
• Fast
• Spectral resolution 1000
• UV->IR
• Cooled < 1K
• Magnetic field + Electric field
• 1 meV electron pair split (1eV for CCD!)
• More depending on energy
wnb060905 BDT-I 66
Info
• C.R. Kitchin, Astrophysical Techniques
(0 7503 0946 6)• http://www.ctio.noao.edu/mailman/listinfo/ccd
-world
• Real life CCD: http://imaging.e2vtechnologies.com
• Experimental Astronomy 2006