Frontend Detectors for the Submm Andrey Baryshev Lecture on 17 Oct 2011 Basic Detection Techniques Submm receivers Part 3 2 Outline Direct detectors principle Photodetectors ID: 720319
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Slide1
Basic Detection TechniquesFront-end Detectors for the Submm
Andrey
Baryshev
Lecture on
17 Oct 2011Slide2
Basic Detection Techniques – Submm receivers (Part 3)
2
Outline
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 NEPSlide3
Basic Detection Techniques – Submm receivers (Part 3)
3
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
Photo detector (electronic)
Bolometric principle
(thermal
detectors)
Coherent detectors (diode)
Other principlesSlide4
Basic Detection Techniques – Submm receivers (Part 3)
4
Parameters of direct detectors
Quantum efficiency
Noise
Linearity
Dynamic range
Number and size of pixels
Time response
Spectral response
Spectral bandwidthSlide5
Basic Detection Techniques – Submm receivers (Part 3)
5
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
contributionSlide6
Basic Detection Techniques – Submm receivers (Part 3)
6
Photon noise and Johnson noise
Detector is limited by statistics of incoming photons
2hc(kT)
1/2
ηλ
qGR
1/2
NEP =
Detector is limited by Johnson noise (thermal fluctuations)
2hc(1/t)
1/2
λ
η
1/2
NEP =Slide7
Basic Detection Techniques – Submm receivers (Part 3)
7
Black body facts
Photon occupation numbers
Uncertainty in
photon numbers
Photon NEP
Stefan-Boltzmann law
M =
σ
T
4
Φ
= 4
π
R
2
L
L= e (2 h f
3
)/(c/n)
2
/(
Exp
(
hf
/(
kT
))-1)Slide8
Basic Detection Techniques – Submm receivers (Part 3)
8
Photo detectors
Arriving photon generate/modify free charge carriers distribution
Classical semiconductor (utilizing band gap)
It has a lower frequency limit
hF
>
E
gap
Typical semiconductor work in IR region
By applying stress to the crystal, it is possible to decrease
E
gap
Like in stressed germanium
SIS junction
No low frequency limit (effective band gap modified by bias point)
High frequency limit due to gap structureKinetic inductance detectors
Photons break Cupper pairsIt has low frequency limit
hF > Egap
ESlide9
Basic Detection Techniques – Submm receivers (Part 3)
9
Example
Detectors PACS instrument on Herschel,
Stressed
germanium bolometersSlide10
Basic Detection Techniques – Submm receivers (Part 3)
10
2
1
CPW Through line
CPW ¼
Resonator
Coupler
Antenna
substrate
Central conductor
100
m
L= 5 mm @ 6 GHz
Al ground plane
Readout signal ~GHz
2
1
KID arrays for Astronomy
Principle of Kinetic Inductance Detection
Pair breaking detector
Superconductor ~ L
KIN
at T<Tc/3
L
KIN
~ N
qp
~ power absorbed
Use L
KIN
to measure absorbed power
KID
a SC material in resonance circuit
read out at F
0
~ 4 GHz
resonance feature is function of N
qp
signal in S
21
or R and
θSlide11
Basic Detection Techniques – Submm receivers (Part 3)
11
KID arrays
KID radiation coupling
Antenna in focus of Si lens
Herschell band 5 & 6
Radiation from sky F
RF
>>2
Δ
/h
-> increases N
qp
-> change in S
21
or R and
θ
F
0
<< F
RF
antenna << resonator
F
0
<< 2Δ/h No qp creation due to readout
Radiation
Si Lens
2
1
CPW Through line
CPW ¼
Resonator
Coupler
Antenna
substrate
Central conductor
100
m
L= 5 mm @ 6 GHz
Al ground plane
Most sensitive area
Readout signal ~GHz
2
1Slide12
Basic Detection Techniques – Submm receivers (Part 3)
12
KID arrays
Principle of KID arrays
Resonances @ F
0
F
0
set by geometry (length)
Intrinsic FDMSlide13
Basic Detection Techniques – Submm receivers (Part 3)
13
KID arrays for astronomy
General idea for the FP
Optical Interface
flies eye array of Si lenses, size 20
F
λ
/2.
90.6% packing efficiency in hexoganal
Array
Detectors printed on back Si lens array
Readout
4 SMA coax connectors
2 full chains -> redundancy
~5000 pixel
0.48 mmSlide14
Basic Detection Techniques – Submm receivers (Part 3)
14
KID focal plane for NIKA
400 pixel test array for 2 mm
antenna
KID
Through lineSlide15
Basic Detection Techniques – Submm receivers (Part 3)
15
Pair breaking detector: fundamental sensitivity limit
DOS
e-p coupling
# quasiparticles
quasiparticle lifetime
1 sec
Pmax/NEP>10.000Slide16
Basic Detection Techniques – Submm receivers (Part 3)
16
Measuring Dark NEP
~
IQ
Synthesizer
Quadrature mixer
Re
Im
ADC
analyses
Superconductor
Shorted end
Open end,
coupler
1
2
Cryostat
LNA
Measure bare resonators
Measure all ingredienst of NEP
Quasiparticle lifetime
qp
noise S
x
Quasiparticle response
δ
x/
δ
N
qp
For R and
θ
Noise Signal qp roll-off
θ
or RSlide17
Basic Detection Techniques – Submm receivers (Part 3)
17
SIS photon detector
17
photon
Δ
E
E
F
qV
・
High sensitive in far-IR – sub-mm region
q
: elementary charge
h:
plank constant
ν
:frequency
I
sg
: subgap current
η
:
quantum efficiency
Superconductor
Bias voltage,
V
Insulator
Superconductor
@ 600 GHz
Our goal:
Current status: 10
-16
~
10
-17
W/
√
Hz
SIS junction
Density of statesSlide18
Basic Detection Techniques – Submm receivers (Part 3)
18
Comparison with theoretical value
(1)
10/17/2011
18
4.2 K
1.6 K
Bias voltage [ V ]
Current [ A ]
D(E)
:density of states,
F(E)
: Fermi function, Δ: gap energy
Nb
/Al-
AlN
/
Nb
junction
Tinkham
(1975)
Theoretical curvesSlide19
Direct
Detection
of
Radiation
Best
Sensitivity
direct
Detection
&
low
Temperatures
Bandpass
Filter (Absorber,
Antenna)
Detector Amplifier
Signal
Filter
Output
Noise:
Noise
Equivalent
Power
(
NEP
) T
Energy
Resolution:
2
1
0
2
1
2
ln
2
2
-
¥
÷
÷
ø
ö
ç
ç
è
æ
×
=
D
ò
df
NEP
ESlide20
Spectral Bandwidth
:
Absorber and Coupling to Thermometer
very high:
l
~ 10
-3
m...10
-12
m
E
Ph
~ meV...MeV
Thermal Conductance G to bath T
Bath
= const.
Thermometer
Absorber with Heat
Capacitance C
D
T =
f
( C, G, E
Ph
,
F
Ph
)
t
Th
=
f
( C, G,… )
Incident Radiation
E
Ph
,
F
Ph
,
t
Ph
C (
T/
t) + G (T
TES
- T
Bath
) = P
Abs
(t) + P
Meas
(t)
Slide21
t
Th
t
Ph
:
“Quantum Calorimeter“
Thermal Conductance G to bath T
Bath
= const.
Thermometer
Absorber with Heat
Capacitance C
D
T =
f
( C, G, E
Ph
,
F
Ph
)
t
Th
=
f
( C, G,… )
Incident Radiation
E
Ph
,
F
Ph
,
t
Ph
t
Th
t
Ph
:
“Bolometer“
C (
T/
t) + G (T
TES
- T
Bath
) = P
Abs
(t) + P
Meas
(t)
Slide22
Operation at low Temperatures
4.2 K
for high signal & fast detector for low noise power:
D
T
,
t
Th
C
NEP
= 4 k
B
T
2
G
G
C , G
T
n
, n > 1
Quantum Calorimeter
Bolometer
D
T
=
(
E
Ph
/
C
)
1/(1 - i
/
w
t
Th
)
D
T
=
(
F
Ph
/
G
)
1/(1 + i
w
t
Th
)
Energy dispersive detection of Power sensitive detection
rapid temperature change of quasi-dc photon flux Slide23
Thermometer:
high sensitivity & high dynamic range
compatible with T
4.2 K
& low power dissipation
transducer temperature
electrical signal
Superconducting Phase Transition Thermometer
Transition Edge Sensor (TES)
TES Thermometer
Thermometer
Absorber C
T
Bath
Low-
Tc
Superconductors
Nb
9K
Al
1K
Mo
0.92 K
Ti
0.4 K
Ir
150 mK
W
15 mK...150mK
Slide24
TES Thermometer
TES Thermometers:
high & positive
a
sensitive temperature-to-resistance transducers
low ohmic, i.e., voltage bias & current readout
negative
Electro-Thermal-Feedback
Resistive Thermometers
R = R
0
T
n
a
= (T/R)
R
/
T = n
T < 4.2K:
TES:
a
10...1000
Normal Metals:
a
0.001
Semiconductor:
a
-0.1..-1Slide25
TES Thermometer with ETF
Negative Electro-Thermal Feedback
Linearized
TES response:
D
P
ABS
=
-
D
P
Joule
(for very strong n-ETF)
Faster
TES response:
t
Th
ETF
3 (C/G) /
a
(Calorimeter count rate )
„Voltage Bias“
R
TES
V
TES
=const.
I
TES
T
TES
P
Joule
/
T
< 0
negative
ETF
in transition region:
D
P
ABS
D
T
D
R
TES
P
Joule
= - I
TES
V
TES
a
T
/
T
TES
C (
T/
t)
+
G (T
TES
- T
Bath
) =
P
ABS (t)
+ PJoule (t) Slide26
TES readout with SQUIDs
R
TES
I
Bias
R
Bias
D
I
TES
SQUIDs
:
current
sensor for TESs
low temperature compatible,
low power dissipation
(<1nW)
highly sensitive
(
pA
resolution)
& high bandwidth
(dc – MHz)
Elektrisches
Signal
@ 300K
<4K
Voltage Bias: R
Bias
<< R
TES
R
TES
1m
W
…100m
W
(Cryogenic) current sensor: Z
Noise
R
TESSlide27
Basic Detection Techniques – Submm receivers (Part 3)
27
Transition edge sensor principle
Thin superconducting film as thermometer
Square law power detector
thermal time constant t = C/G
C: thermal capacitance
G: thermal conductivitySlide28
LABOCA (as example)Basic Detection Techniques – Submm receivers (Part 3)
28Slide29
Space TES detectors (SPICA, SAFARI)Basic Detection Techniques – Submm receivers (Part 3)
29
Low G TES
High G TESSlide30
Basic Detection Techniques – Submm receivers (Part 3)
30
Procedure of an NEP measurement
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/Hz
1/2