2014-応用計測学Ⅰ-photon-detectors.ppt [互換モード]

応用計測学Ⅰ応用計測学Ⅰ

担当：松田恭幸（まつだやすゆき）

居室：1 6号館2 2 2 A号室居号館号

t e l : 0 3 - 5 4 5 4 - 6 5 1 4e - m a i l : m a t s u d a y @ p h y s . c . u - t o k y o . a c . j p

h t t / / d h 4 t k j / t dh t t p : / / r a d p h y s 4 . c . u - t o k y o . a c . j p / ~ m a t s u d a y

授業日：毎週金曜３限（１３：００～１４：３０）

第８回・第９回

Photon DetectorPhoton Detector

Photon Detector

Ph t d t ti f (E Photon detection for 100nm ≤ ≤ 1000nm (E~ a few eV) is important for particle detection and high-energy photon detection because this range covers energy photon detection, because this range covers scintillation (explained later) and Cherenkov radiationradiation.

d d h h In order to detect such photons, Generate a primary photoelectron or electron-hole pair Amplify them to detectable levels (millions of electrons) Collect the secondary electrons to form the electric signal

Photon Detector

Important parameters for photon detector Important parameters for photon detector spectrum response : the number of primary photoelectrons (or

electron-hole pairs) per incident photons as a function of wavelengthp ) p p g Gain : the number of electrons collected for each photoelectron

generatedT it ti th ti b t th i l f th h t d th Transit time : the time between the arrival of the photon and the electrical pulse

Rise time and width : determined by the transit time spready p Area : how large area can be covered by a detector Dynamic range : the ratio of the maximum signal and the minimum

i l d t t blsignal detectable $$$ (costs) !

Photomultiplier (PMT)p ( )

A “versatile” photon detector A versatile photon detector. photon hits the cathode and generate photoelectrons

→ photoelectrons are accelerated and guided by electrodes to bombard the dynodebombard the dynode.→ the dynode emits a few secondary electrons. → repeat 8~12 times to generate sufficient number of electrons (t pical gain is 105 106)(typical gain is 105~106)→ collected by anode for the external circuit.

(HAMAMATSU PMT catalog)


Wi d t i l Window materials



Ph t th d t i l Photocathode materials



Dynode types Dynode types Circular-cage type :

compact and fast response relatively low voltage (~800V) operation

Linear-focus type : very fast rise time and small transit time very fast rise time and small transit time

spread good pulse linearity relatively high voltage ( 2000V) relatively high voltage (~2000V)

operation Fine-mesh time :

hi h i i fi ld ( high resistance to magnetic field (up to 1.5 Tesla)

excellent pulse linearity


Pulse-mode operation Pulse-mode operationWhen the flux of photon is very low, the number of counted pulses equals the number of (detected) photons.

hi i l d iThis is pulse-mode operation. DC-mode operation

When the flux of photons is high the output pulses When the flux of photons is high, the output pulses overlap each other, and the amplitude of the signal is proportional to the intensity of the incident light.


Pulse-mode operation Pulse-mode operationWhen the flux of photon is very low, the number of counted pulses equals the number of (detected) photons.

hi i l d iThis is pulse-mode operation. DC-mode operation

When the flux of photons is high the output pulses When the flux of photons is high, the output pulses overlap each other, and the amplitude of the signal is proportional to the intensity of the incident light.


Ti h t i ti Time characteristicsDynodeType

Rise time (ns)

Pulse width (ns)

Transit Time (ns)

Transit Time ypSpread (ns)

Linear-focused

1 to 3 1 to 5 15 to 50 0.3 to 1focused

Circular-cage 3~4 ~7 ~30 ~3

Fine mesh ~3 ~5 ~15 ~ 0.5


Li it Linearity Limited by the space-charge effects

Dependent on the peak signal current : large number of secondary Dependent on the peak signal current : large number of secondary electrons in dynode circuit distort the electric field

Higher voltage, better linearity (if enough current can be supplied)



V lt di id i it Voltage divider circuit Gives each dynode designed potential

Th d t d d d t fl t t d th The anode current and dynode current flow act to reduce the divider current → loss of the interstage voltage

The more incident light increased, the more voltage The more incident light increased, the more voltage distribution being varied.

Rule: Ianode / Idivider < 1/20 ( < 1/100 if <1% linearity required )



V lt di id i it ith “b t ” Voltage divider circuit with “booster” Additional power supplies to increase Idivider

E i Expensive



V lt Di id ith d li it Voltage Divider with decoupling capacitors output charge Q0 per pulse : Q0= TwV0/RL

Q i h t d i C Q Q Q3 is charge stored in C3 : Q3=100Q0

→ C3>100Q0/V3

Usually C = 1 ~ 20 nF Usually C3 = 1 ~ 20 nF Decoupling capacitors needs to be “fast” : electrolytic

capacitors are no good.p g



P ti l di id i it Practical divider circuit R1 and C1 makes a low-pass filter to reduce noise from the

HVPSHVPS R1 ~ a few tens k C1 ~ 0.05F1 5

R9 and R10 to reduce “ringing” in the output R9 and R10 should be as small as possible. typically ~ 10 to 100





M ti Shi ldi Magnetic Shielding -metal (an arroy with high permeability) is often used.

Wh PMT i l d i hi h ti fi ld ith When PMT is placed in higher magnetic field, an arroy with high-saturation (such is steal) should be used in conjunction.

The PMT head should be hidden from the shield edge by a The PMT head should be hidden from the shield edge by a length equal to the shield case radius



PMT’s merit : You can select photocathode materials and PMT s merit : You can select photocathode materials and dynode configuration to optimize for your needs.

Example: UV/Visible/IR Spectrophotometer Wide spectral response Wide spectral response High stability Low dark noise

H t R3896

Cherenkov Counter High quantum efficiency

Hamamatsu R3896

g q y Single photon counting Fast response time High gain High gain

Hamamatsu R329


PMT’ it Y l t h t th d t i l PMT’s merit : You can select photocathode materials and dynode configuration to optimize for your needs.

Hamamatsu R1449(50cm world-largest PMT)

Super-Kamiokande Hamamatsu H10330A(Special photocathode + cooling unit→ sensitive to 950nm ~1700nm))


PMT’ it Y l t h t th d t i l PMT’s merit : You can select photocathode materials and dynode configuration to optimize for your needs.

“Logging-while-drilling” for oil wellsA radiation source and a scintillator/PMT is placed

under the drill. The scattered radiation and natural

PMT under High temperature ( 200C) and vibration

radiation is monitored to determine the type and density of the rock.

High temperature (~200C) and vibration

Multichannel plate (MCP)p ( )

2mm thick glass plates with 10m-diameter holes (channels) 2mm thick glass plates with 10m diameter holes (channels), separated by 1mm gaps.

Fast response time, excellent time resolution, High resistance to magnetic field High resistance to magnetic field Good spatial resolution MCP is usually used in “saturation” mode – each channel can give

onl on/off o tp t b t the s m of all channel o tp ts remains only on/off output, but the sum of all channel outputs remains proportional to the number of photons received on the surface of MCP. In this mode, MCP has good linearity.


Photodiode (PD)( )

Photodiode is a reverse-biased p-n junction Photodiode is a reverse biased p n junction Photons with energies above the bandgap energy (Eg) create eh

pairs. Eg of Si in room temperature is 1.12eV (~1100nm) In the depletion layer the electric field accelerates electrons toward In the depletion layer, the electric field accelerates electrons toward

the N-layer, and holes toward the P-layer, charges are collected at the end.

Number of eh pairs are in proportion to the amount of light Number of eh pairs are in proportion to the amount of light. No gain in the photodiode (usually amplification is necessary)

(HAMAMATSU PD catalog)

Photodiode (PD)( )

Quantum efficiency can exceed 90% around 900nm Quantum efficiency can exceed 90% around 900nm The response time is very fast. The minimum detectable signal in room-temperature device is

l h d d h (li i d b h l i )several hundred photons (limited by thermal noise) Low-noise amplifiers are slow → trade-off between noise level and response time.p

(HAMAMATSU PD catalog)

Avalanche Photodiode (APD)( )

Linear-mode operationLinear mode operation Large reversed-bias on a p-n junction.

→ Accelerated carriers have enough energy to generate new eh pairs→ Avalanche eh of initiates but still the number of total eh holes is → Avalanche e h of initiates, but still the number of total e h holes is proportional to the amount of light.

Gain ~ 100.

Geiger-mode operation Further increase reversed-bias

→ Total signal is constant. (determined by small register connected in Total signal is constant. (determined by small register connected in series)

Gain ~ 105~7

Common for both modes APD can detect a single photon (↔ several hundreds photons needed for a

photodiode) Response time is very fast (<1nsec)

MPPC

M lti Pi l Ph t C t (MPPC) Multi-Pixel Photon Counter (MPPC) also called as PPD (Pixelized Photon Detector), SiPM (Silicon

Photomultiplier)Photomultiplier) 2D Arrays of APDs Each cell gives binary output, but the the sum of the cell Each cell gives binary output, but the the sum of the cell

outputs is proportional to the number of photons (just like MCP)

Gain ~ 106

Single photon counting possible. i h i i fi ld High resistance to magnetic field.

R&D t bi th MPPC d th f t d l t i i R&D to combine the MPPC and the front-end electronics in one-chip.

Other special semiconductor-based detectorsp

VLPC (used in FermiLab’s D0 experiment) VLPC (used in FermiLab s D0 experiment) APD (linear-mode) with As-doped Si, which has an impurity

band 50meV below the conduction band.5 Large Gain (~5104) Signal proportional to the amount of light Very large noise →needs cooling below 10K

Di d d t t Diamond detector PD arrays based on diamond films formed by CVD (chemical

vapor deposition).vapor deposition). Sensitive to UV region. Little radiation damage, small temperature dependence

Hybrid photon detector (HPD)y p ( )

Combine the high sensitivity (and large area) of PMT with the Combine the high sensitivity (and large area) of PMT with the excellent energy resolution of Si APD.

A photoelectron is accelerated to ~10keV before impinges on the silicon anode. silicon anode. → Electron-hole pairs generated according to the incident energy.

time resolutions of ~10psece tremel good p lse height resol tion (Gain fl ct ation is extremely good pulse height resolution (Gain fluctuation is extremely small)

does not work in magnetic fieldhi h l ( k V) d d high voltage (~10keV) needed.

Summary of photon detectors (Eph~eV)y p ( ph )

PMT : the “standard” device PMT : the standard device. Large selection of photocathode materials and dynode configuration

to optimize for the specific requirements. Single photon counting possible Single-photon counting possible. Very large areas can be covered by one module Dynamic range is very good.

PD : Good for intense light source detection APD : Single-photon counting possible covers small APD : Single photon counting possible, covers small

area. MPPC : a good alternative to PMT. Compact, lightweight, tolerant to magnetic field Dynamic range is rather small, and noise level is relatively high.

Summary of photon detectors (Eph~eV)y p ( ph )

Recent progress on Solid-state photon detectors makes Recent progress on Solid-state photon detectors makes them superior to PMTs for many existing applications regarding their size, weight, tolerance to magnetic field, and costsand costs.

R&D for some hybrid devices to combine the best features of different technologies is on going (like HPD).g g g ( )

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2014-応用計測学Ⅰ-photon-detectors.ppt [互換モード]