Transcript SRON presentation - University of Groningen

Basic Detection Techniques
Front-end Detectors for the Submm
Andrey Baryshev
Lecture on 17 Oct 2011
Outline
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Direct detectors (principle)
• Photo-detectors
• Bolometers
• Other types (pyro-detectors, Golay cell)
Noise in direct detectors
• NEP -- noise equivalent power
• Photon noise
• Electronics noise
Low noise detectors in submm THz region
• Transition edge sensors
• Kinetic inductance detectors
• SIS junction as direct detector
• TES bolometer
Practical measurement of NEP
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Direct detector principles
Direct detector gives signal proportional to the power of incoming
radiation or amount of photons.
Usually detector pixel is much simpler than heterodyne
counterpart, so large arrays are possible
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Photo detector (electronic)
Bolometric principle (thermal detectors)
Coherent detectors (diode)
Other principles
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Parameters of direct detectors
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Quantum efficiency
Noise
Linearity
Dynamic range
Number and size of pixels
Time response
Spectral response
Spectral bandwidth
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NEP
NEP is power at the input of the detector to produce
SNR=1
One can add the contributions of different noise sources
in square fashion as in the formula above for optics noise
contribution
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Photon noise and Johnson noise
Detector is limited by statistics of incoming photons
NEP =
2hc(1/t)1/2
λ η1/2
Detector is limited by Johnson noise (thermal fluctuations)
NEP =
2hc(kT)1/2
ηλqGR1/2
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Black body facts
Uncertainty in
photon numbers
Photon occupation numbers
Photon NEP
Φ = 4 π R2 L
M = σT4
L= e (2 h f3)/(c/n)2 /(Exp(hf/(kT))-1)
Stefan-Boltzmann law
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Photo detectors
Arriving photon generate/modify free charge
carriers distribution
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Classical semiconductor (utilizing band gap)
• It has a lower frequency limit hF > Egap
• Typical semiconductor work in IR region
• By applying stress to the crystal, it is
possible to decrease Egap Like in stressed
germanium
SIS junction
• No low frequency limit (effective band gap
modified by bias point)
• High frequency limit due to gap structure
Kinetic inductance detectors
• Photons break Cupper pairs
• It has low frequency limit
E
hF > Egap
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Example
Detectors PACS instrument on Herschel,
Stressed germanium bolometers
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KID arrays for Astronomy
Principle of Kinetic Inductance Detection
Antenna
Pair breaking detector
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Superconductor ~ LKIN at T<Tc/3
LKIN ~ Nqp ~ power absorbed
Use LKIN to measure absorbed power
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KID
a SC material in resonance circuit
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CPW ¼  Resonator
L= 5 mm @ 6 GHz
read out at F0 ~ 4 GHz
resonance feature is function of Nqp
signal in S21 or R and θ
Im R
S21 [dB]
Al ground plane
Re
f
F0
100 m

CPW Through line
F [Ghz]
1
Readout signal ~GHz
substrate
Coupler
Central conductor
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KID arrays
KID radiation coupling
Antenna
Antenna in focus of Si lens
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Herschell band 5 & 6
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Radiation from sky FRF >>2Δ/h
Most sensitive area
-> increases Nqp
-> change in S21 or R and θ
CPW ¼  Resonator
L= 5 mm @ 6 GHz
F0 << FRF
antenna << resonator
F0 << 2Δ/h
No qp creation due to readout
Si Lens
Al ground plane
100 m
Radiation
CPW Through line
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Readout signal ~GHz
substrate
Coupler
Central conductor
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KID arrays
Principle of KID arrays
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Resonances @ F0
F0 set by geometry (length)
Intrinsic FDM
no light
LED on
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-20
S21 [dB]
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-25
-30
-35
4.056
4.058
4.060
4.062
4.064
4.066
4.068
F [GHz]
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KID arrays for astronomy
General idea for the FP
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Optical Interface
flies eye array of Si lenses, size 20Fλ/2.
90.6% packing efficiency in hexoganal
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Array
Detectors printed on back Si lens array
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Readout
4 SMA coax connectors
2 full chains -> redundancy
~5000 pixel
0.48 mm
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KID focal plane for NIKA
400 pixel test array for 2 mm
antenna
KID
Through line
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Pair breaking detector: fundamental sensitivity limit
# quasiparticles
DOS
NEP  2  N (T) / (T)
quasiparticle lifetime
NEP [W/Hz]
NEP
1E-13 Nqp
  
N0
~ 2 
T  exp

0
k
T
 B 
e-p coupling
Pmax/NEP>10.000
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1E-14 
10
1E-15
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1E-16
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1E-17
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1E-18
10
1E-19
10
1E-20
10
1E-21
10
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1 sec
 [nsec] or Nqp
0
3
2
1
1E-22
10
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
T/Tc
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Measuring Dark NEP
Noise
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Signal
 qp x
NEP  S x ()  
  N
qp

Measure bare resonators
Measure all ingredienst of NEP
Quasiparticle lifetime qp
noise
Sx
Quasiparticle response δx/δNqp
For R and θ
θ or R
1

  1  2  2 qp


Im R
Re
Cryostat
qp roll-off

Shorted end
Synthesizer
Superconductor
~
1
Open end,
coupler
Quadrature
mixer
Re
2
ADC
IQ
LNA
analyses
Im
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・High sensitive in far-IR – sub-mm region
SIS junction
Bias voltage, V
Superconductor
Superconductor
photon
q
S  
[A/W]
h
N  2qI sg [A/ Hz ]
Insulator
E
Density of states
qV
h  qV  2
EF
Δ
q: elementary charge
h:plank constant
ν:frequency
Isg: subgap current
η: quantum efficiency
N h 2 I sg
NEP  

[W/ Hz ]
S 
q
Current status: 10-16 ～10-17 W/√Hz
Our goal:
NEP  10 19 W/ Hz @ 600 GHz
for I sg  10 fA,   0.5
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D(E):density of states, F(E): Fermi function, Δ: gap energy
Tinkham (1975
Current [ A ]
Nb/Al-AlN/Nb junction
7/17/2015
4.2 K
1.6 K
Theoretical curves
Bias
voltage [ V ]
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Direct Detection of Radiation
Detector
Amplifier
Filter
Output
Signal
Bandpass Filter (Absorber, Antenna)
• Noise:
Noise Equivalent Power (NEP )  T


1


 E  2 2ln2   
2 df 
 0 NEP
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
• Energy Resolution:
1 2
Best Sensitivity  direct Detection & low Temperatures
Incident Radiation
EPh, FPh, Ph
Thermometer
T = f ( C, G, EPh, FPh)
Th = f ( C, G,… )
Absorber with Heat
Capacitance C
Thermal Conductance G to bath
TBath = const.
C ( T/  t) + G (TTES - TBath) = PAbs (t) + PMeas (t)
Spectral Bandwidth :
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Absorber and Coupling to Thermometer
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very high:
 ~ 10-3 m...10-12 m
EPh ~ meV...MeV
Incident Radiation
EPh, FPh, Ph
Thermometer
T = f ( C, G, EPh, FPh)
Th = f ( C, G,… )
Absorber with Heat
Capacitance C
Thermal Conductance G to bath
TBath = const.
C ( T/  t) + G (TTES - TBath) = PAbs (t) + PMeas (t)
Th  Ph :
Th  Ph :
“Quantum Calorimeter“
“Bolometer“
Quantum Calorimeter
Bolometer
T = (EPh / C ) 1/(1 - i /  Th)
T = (FPh / G ) 1/(1 + i  Th)
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Energy dispersive detection of
rapid temperature change
Power sensitive detection
of quasi-dc photon flux
for high signal & fast detector
for low noise power:
T  , Th   C 
NEP = 4 kB T 2 G  G 
C , G  Tn, n > 1
 Operation at low Temperatures  4.2 K
TES Thermometer
Thermometer
Absorber C
• Thermometer:
high sensitivity & high dynamic range
compatible with T  4.2 K & low power dissipation
transducer temperature  electrical signal
TBath
 Superconducting Phase Transition
Thermometer
Transition Edge Sensor (TES)
Low-Tc Superconductors
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a = (T/R)  R/ T
Resistance R / a.u.
3
0
0
2
2
1
Temperature T / K
Nb  9K
Al  1K
Mo  0.92 K
Ti  0.4 K
Ir  150 mK
W  15 mK...150mK
TES Thermometer
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a = (T/R)  R/ T
Resistance R / a.u.
3
0
0
2
2
1
Temperature T / K
Resistive Thermometers
R = R0Tn
a = (T/R)  R /  T = n
T < 4.2K:
TES: a  10...1000
Normal Metals: a  0.001
Semiconductor: a  -0.1..-1
TES Thermometers: high & positive a
 sensitive temperature-to-resistance transducers
 low ohmic, i.e., voltage bias & current readout
 negative Electro-Thermal-Feedback
TES Thermometer with ETF
„Voltage Bias“
VTES=const.
• C ( T/  t) + G (TTES - TBath) = PABS (t) + PJoule (t)
ITES
RTES
TTES
• in transition region: PABS  T  RTES
PJoule = - ITES VTES a T / TTES
PJoule / T < 0  negative ETF
Negative Electro-Thermal Feedback
 Linearized TES response:
PABS = -PJoule (for very strong n-ETF)
 Faster TES response:
ThETF  3 (C/G) / a
(Calorimeter count rate )
TES readout with SQUIDs
IBias
• Voltage Bias: RBias << RTES
• RTES  1mW…100mW
RTES
RBias
• (Cryogenic) current sensor: ZNoise  RTES
ITES

<4K
Elektrisches
Signal
@ 300K
SQUIDs : current sensor for TESs
 low temperature compatible, low power dissipation
 highly sensitive
(pA resolution)
& high bandwidth
(<1nW)
(dc – MHz)
Transition edge sensor principle
Thin superconducting film as
thermometer
Square law power detector
thermal time constant t = C/G
C: thermal capacitance
G: thermal conductivity
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LABOCA (as example)
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Space TES detectors (SPICA, SAFARI)
Low G TES
High G TES
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Procedure of an NEP measurement
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Determine the signal power
• It is given by Planck formula
• Need temperature of calibrator black-bodies
• Frequency coverage of the detector (measured by FTS)
• Knowledge of solid angle of antenna beam pattern
Determine the responsively
• Measure response from hot/cold radiators
• Calibrate detector output in input power units
Determine the background noise
• Block connect the detector beam to as little background –
possible
• Measure time trace and using responsively and integration
time express it in NEP Wt/Hz1/2
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