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Basic Detection

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Bolometers. Most basic detector type: a simple absorber ... Bolometer. wnb060905. BDT-I. 38. Detectors 2. Coherent Detectors ... – PowerPoint PPT presentation

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Title: Basic Detection


1
Basic Detection Techniques
2
Detector
  • More than sensing device
  • Measuring
  • Meten is weten
  • Meta information
  • Counting vs analog

3
Poisson
4
Gaussian

5
Accuracy
  • Distribution stochastic measurement process only
  • Precision
  • Accuracy -gt no systematic
  • Hubble
  • Target shooting

6
Statistics
  • Mean
  • Variance
  • Chi-squared
  • Median

7
Moments
  • Central moments
  • skewness

8
Systematic errors
  • Instrument environment widest sense
  • Coal
  • Parallax
  • Gaia
  • Gal rotation
  • Pressure
  • Model -gt none
  • Outliers

9
Modelling
  • Solve
  • L2 (least-squares)
  • L1 (outliers)

10
(In)direct
  • Direct
  • Raindrops
  • Planet directly
  • Indirect
  • Crop size
  • systematic movement of Centre of G.
  • Test particle

11
Measurables
  • EM waves
  • Neutrinos
  • Matter (nuclei -gt meteorites space craft)
  • Gravitational waves (ltc)

12
Neutrinos
Weak interaction electron neutrinos
Strong interaction Tau muon neutrinos
13
Neutrinos 2
  • Long pathlength -gt memory
  • 1931 Pauli 1959 e 1962 new muon
  • Indirect
  • Icecube
  • Ocean
  • Moon

14
Neutrino 3
                                                                          
                                       
  • Solar problem
  • 1987 SN -gt 19 neutrinos (water, proton decay)
  • 50000 tons 11000 PMT (50cm)
  • Mass lt 2.2eV

15
Cherenkov
16
GW
  • 10-38 weaker than EM force
  • Transparant universe
  • Tensor (cf vector and potential)
  • Helicity -2 (-1)

17
GW 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

18
Matter
  • Cosmic Rays (later lecture)
  • Pierre Auger (AR) Northern
  • LOFAR
  • Meteorites -gt history
  • Returning spacecraft

19
EM radiation
  • Energy wavelength frequency
  • Flux
  • Time variation
  • Spatial dependence
  • Polarisation
  • Only directional measurement (magnetic field)
  • Resolution in all
  • Uncertainty
  • aperture

20
EM radiation
  • Not all simultaneous -- choose

21
Spectrum
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

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

24
Measure
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?
25
Flux 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
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
27
Flux 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

28
Planck
29
Planck 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

30
Stars

31
IR windows
µm
32
Atmosphere transmission
33
QE
Eye 10-20
Photographic 2-10
CCD 70-90
PMT 20-30
IR (HgCdTe) 30-50
CMOS 60-80
34
QE(2)
35
Spectrum
36
Detectors
  • 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)

37
Bolometer
38
Detectors 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

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)

40
Detector 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

41
Detector 5
  • Chemical detectors
  • Eye
  • Photographic plate

42
Eye
  • Rods (10-20)
  • Cones (1-2) 3 varieties
  • 1ps response 1/20s integration 15min to
    revitalise
  • Flashes

43
Photographic
  • - non-linear
  • - low dynamic range
  • pixels
  • Photon excites e AgCl -gt Ag- into Ag.(defect)
  • Developing amplification
  • Slow (but stroboscopic)

44
PMT
45
PMT-a
46
PMT2
  • QE 5-10
  • UV/B poor in R/IR

47
MCP
48
MCP2
  • QE 20
  • Can be staggered (chevron)
  • Up to million amplification
  • 1-1000nm

49
IPCS
  • 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

50
Image intensifier
51
CCD
  • Charge Coupled Device

52
CCD layout
53
CCD transfer
54
CCD readout
55
CCD
  • 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

56
CCD2
  • Large 10.5 10.5 kpixel
  • 4 stitched -gt 500 million pixels
  • Thinned back-illuminated no reflection
  • Thinned very expensive fragile, but efficient

57
CCD perfect?
Cosmic rays Hot Spots (high dark current, but some
times LEDs!) Bright Column (charge traps)
Dark Columns (charge traps) QE variations
58
CMOS
  • Complementary Metal Oxide Silicon
  • Direct readout
  • But 15-30 photomasks rather than 10 for CCD

59
CMOS 2
60
NIR (hybrid)
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)

62
SIS BIB - SSPM
  • Superconductor-Insulator-Superconductor tunnel
    junctions
  • Blocked-Impurity-Band detectors
  • Solid-State-PhotoMultipliers
  • Josephson junctions

63
Energy resolving STJ/TES
64
STJ
  • 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

65
Tip-tilt CCD wavefront
66
Info
  • 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
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