Title: Basic Detection
1Basic Detection Techniques
2Detector
- More than sensing device
- Measuring
- Meten is weten
- Meta information
- Counting vs analog
3Poisson
4Gaussian
5Accuracy
- Distribution stochastic measurement process only
- Precision
- Accuracy -gt no systematic
- Hubble
- Target shooting
6Statistics
- Mean
- Variance
- Chi-squared
- Median
7Moments
8Systematic errors
- Instrument environment widest sense
- Coal
- Parallax
- Gaia
- Gal rotation
- Pressure
- Model -gt none
- Outliers
9Modelling
- Solve
- L2 (least-squares)
- L1 (outliers)
10(In)direct
- Direct
- Raindrops
- Planet directly
- Indirect
- Crop size
- systematic movement of Centre of G.
- Test particle
11Measurables
- EM waves
- Neutrinos
- Matter (nuclei -gt meteorites space craft)
- Gravitational waves (ltc)
12Neutrinos
Weak interaction electron neutrinos
Strong interaction Tau muon neutrinos
13Neutrinos 2
- Long pathlength -gt memory
- 1931 Pauli 1959 e 1962 new muon
- Indirect
- Icecube
- Ocean
- Moon
14Neutrino 3
- Solar problem
- 1987 SN -gt 19 neutrinos (water, proton decay)
- 50000 tons 11000 PMT (50cm)
- Mass lt 2.2eV
15Cherenkov
16GW
- 10-38 weaker than EM force
- Transparant universe
- Tensor (cf vector and potential)
- Helicity -2 (-1)
17GW 2
- Direct resonant
- Block gt 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
18Matter
- Cosmic Rays (later lecture)
- Pierre Auger (AR) Northern
- LOFAR
- Meteorites -gt history
- Returning spacecraft
19EM radiation
- Energy wavelength frequency
- Flux
- Time variation
- Spatial dependence
- Polarisation
- Only directional measurement (magnetic field)
- Resolution in all
- Uncertainty
- aperture
20EM radiation
- Not all simultaneous -- choose
21Spectrum
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
23Sensitivity
- 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
24Measure
Flux is the energy incident per unit time per
unit area within a defined EM band f Ein
band/A t (or power per unit area) Usually quoted
at top of Earths atmosphere
o Bolometric all frequencies o Finite bands
(typically 1-20) defined by, e.g., filters
such as U,B,V,K o Monochromatic infinitesimal
band, ? ? ? d? Also called spectral flux
density Denoted f? or f? Note conversion since
f?d? f?d? and ? c/?, ? ?f? ?f?
25Flux 2
1 Jy 10-26 W m-2 Hz-1 10-23 erg s-1
cm-2 Hz-1 non SI
Monochromatic Apparent Magnitudes o m? -2.5
log10 f? - 21.1, where f? 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.
m?(5500 A) V o Zero Point fluxes at 5500 A
corresponding to m?(5500A) 0, are (Bessell
1998) f0 ? 3630 Jy (janskys) or 3.63 10-20
erg s-1 cm-2 Hz-1 ?/h? 1005 photons cm-2 s-1
A-1 is the corresponding photon rate per unit
wavelength
26Flux 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
27Flux 4
- Luminosity L (W)
- Power (energy/s) radiated by source into 4p
sterad - Flux (W m-2)
- f L/4pD2 if source isotropic, no absorption
- Brightness I (W m-2 sr-1)
- f I?O
28Planck
29Planck 2
- Limiting forms
- h?/kT ltlt 1 ? B?(T) 2kT /?2 (Rayleigh-Jeans)
- h?/kT gtgt 1 ? B?(T) 2h?3 e-h?/kT /c2 (Wien)
- Non-thermal
- T gt 1020
30Stars
31IR windows
µm
32Atmosphere transmission
33QE
Eye 10-20
Photographic 2-10
CCD 70-90
PMT 20-30
IR (HgCdTe) 30-50
CMOS 60-80
34QE(2)
35Spectrum
36Detectors
- Bolometers
- 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)
37Bolometer
38Detectors 2
- Coherent Detectors
- Multiparticle detection of electric field
amplitude of incident - EM wave
- Phase information preserved
- Frequency band generally narrow but tuneable
- Heterodyne technique mixes incident wave with
local - oscillator
- Response proportional to instantaneous power
collected in - band
- Primarily radio, millimetre wave, but some IR
systems with - laser LOs
39Detectors 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) -
40Detector 4
- UVOIR, X-ray, Gamma-ray
- o Photo excitation devices photon absorption
changes - distribution of electrons over states. E.g.
CCDs, - photography
- o Photoemission devices photon absorption causes
- ejection of photoelectron. E.g. photocathodes
and - dynodes in photomultiplier tubes.
- o High energy cascade devices X- or gamma-ray
- ionization, Compton scattering, pair-production
produces multiparticle pulse. E.g. gas
proportional counters, scintillators
41Detector 5
- Chemical detectors
- Eye
- Photographic plate
42Eye
- Rods (10-20)
- Cones (1-2) 3 varieties
- 1ps response 1/20s integration 15min to
revitalise - Flashes
43Photographic
- - non-linear
- - low dynamic range
- pixels
- Photon excites e AgCl -gt Ag- into Ag.(defect)
- Developing amplification
- Slow (but stroboscopic)
44PMT
45PMT-a
46PMT2
- QE 5-10
- UV/B poor in R/IR
47MCP
48MCP2
- QE 20
- Can be staggered (chevron)
- Up to million amplification
- 1-1000nm
49IPCS
- TV photo electron (from Si) stored in
micro-capacitors - Scanned/recharged 25Hz -gt discharge current
- High readout noise (snow)
- 1st intensifier 3 stage million gain
- Read out photon counting digital
50Image intensifier
51CCD
52CCD layout
53CCD transfer
54CCD readout
55CCD
- Workhorse up to 1.1 um -gt bandgap
- Dynamic range bits 300001
- Linearity same
- Read-out noise 2-3 e-
- Dark current (thermal) -gt cool
- Shot noise random photons
- Non-uniformity -gt flat fielding
- Charge transfer efficiency (gt.99999 has to be)
- Cosmic rays pixel error
56CCD2
- Large 10.5 10.5 kpixel
- 4 stitched -gt 500 million pixels
- Thinned back-illuminated no reflection
- Thinned very expensive fragile, but efficient
57CCD perfect?
Cosmic rays Hot Spots (high dark current, but some
times LEDs!) Bright Column (charge traps)
Dark Columns (charge traps) QE variations
58CMOS
- Complementary Metal Oxide Silicon
- Direct readout
- But 15-30 photomasks rather than 10 for CCD
59CMOS 2
60NIR (hybrid)
61NIR
- 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)
62SIS BIB - SSPM
- Superconductor-Insulator-Superconductor tunnel
junctions - Blocked-Impurity-Band detectors
- Solid-State-PhotoMultipliers
- Josephson junctions
63Energy resolving STJ/TES
64STJ
- Fast
- Spectral resolution 1000
- UV-gtIR
- Cooled lt 1K
- Magnetic field Electric field
- 1 meV electron pair split (1eV for CCD!)
- More depending on energy
65Tip-tilt CCD wavefront
66Info
- C.R. Kitchin, Astrophysical Techniques
- (0 7503 0946 6)
- http//www.ctio.noao.edu/mailman/listinfo/ccd-worl
d - Real life CCD http//imaging.e2vtechnologies.com
- Experimental Astronomy 2006