1 Development of Multi-Pixel Photon Counters (1) S.Gomi, T.Nakaya, M.Yokoyama, M.Taguchi, (Kyoto University) T.Nakadaira, K.Yoshimura, (KEK) Oct Hawaii for KEK-DTP photon sensor group

2 Contents Introduction Measure the fundamental performance –Check the MPPC raw signal –GAIN –noise rate –Cross-talk rate –Photon Detection Efficiency ( PDE ) –Linearity LASER test( KEK-DTP LASER system)

3 Introduction

4 Multi-Pixel Photon Counter ( MPPC ) Multi-Pixel Photon Counter ( = MPPC ) is a new type of photo detector developed by Hamamatsu Photonics (HPK). MPPC consists of 100~1600 small avalanche photo diodes( APD ) in 1mm×1mm sensitive region. MPPC 1pixel Sensitive region of MPPC 400pixel type 6mm

5 Operation principle of MPPC Each APD pixel operate in Geiger mode. Gain is proportional to the applied voltage above the breakdown voltage( V bd ). V V bd In Geiger mode, the output charge Q from a single pixel is independent of the number of injected photons within the pixel. Extrapolated to GAIN=0

6 6mm 5mm MPPC character Combining the output from all the pixels, the total charge from one MPPC is quantized to multiples of Q. MPPC advantages –Compact –Insensitive to magnetic field –High gain( ~10 6 ), low bias voltage( ~70V ) –Low-cost We measured the basic performance of two kinds of MPPC, 100 pixel type, and 400 pixel type. the MPPC is an excellent photon counting device

7 Measure the fundamental performance check the MPPC raw signal gain noise rate cross-talk rate Photon Detection Efficiency ( PDE ) Linearity

8 The raw signal of MPPC MPPC has good photon counting capability. We can observe 1p.e signal peak, 2p.e signal peak, … * ADC distribution * pedestal 1p.e signal 2p.e 3p.e 4p.e … 1p.e 2p.e …

9 set up Measuring the little light from the blue LED by MPPC. Gain is measured by ADC distribution. blue LED MPPC Gain The gain can be estimated at intervals between 1p.e and the pedestal. ADC distribution * STATUS DATA * 400 pixel MPPC BIAS : 70.0V / V BD =68.8V Gain of MPPC is defined as this equation. Gain is measured by analyzing ADC distributions of MPPC signals. pedestal 1p.e signal 2p.e 3p.e 4p.e …

10 Gain From gain-voltage relation, the break down voltage can be measured. Blue: 15degree Green: 20degree Red: 25degree MPPC is a high gain device. MPPC is a high gain device. The break down voltage depends on the temperature. Gain 400pixel Bias voltage [V] Gain 100pixel Bias voltage [V]

11 Gain Gain is a function of  V. Blue: 15degree Green: 20degree Red: 25degree Gain 400pixelGain 100pixel VV VV

12 Noise rate MPPC is a noisy photo detector. The origin of these noises is the thermo electron. So, the signals of noise are 1p.e signal typically. The noise rate is measured by counting the rate of signal with their height over the threshold, imposed on 0.5p.e and 1.5p.e. Noise signal of 100pixel MPPC at 25 degree. ( integrated ) 1 p.e 0.5 p.e = threshold 1.5 p.e = threshold “ 1p.e noise ” “ 2p.e noise ”

13 Noise rate 1p.e noise rate is about 100~400 kHz. 2p.e noise rate is about 0~200 kHz. 100kHz 400kHz Bias voltage [V] Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel 100kHz 500kHz Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree 1p.e noise 2p.e noise 1p.e 2p.e

14 Blue: 15degree Green: 20degree Red: 25degree Noise rate 1p.e noise rate is a function of both temperature and  V. 100kHz 400kHz Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel 100kHz 500kHz p.e 2p.e 2p.e noise rate seem to be a function of  V. This is due to “Cross-talk”. VV VV 1p.e 2p.e

15 Cross-talk rate. The origin of the cross-talk is presumed to be optical photons emitted during avalanche which enter neighboring pixels and trigger another Geiger discharge. APD that should not detect any photons from outside also operate signals. “ Cross-talk “ Neighborhood pixel   Avalanche

16 The probability of cross-talk is estimated by the number of 1p.e. Cross-talk rate measurement The cross talk rate is determined. The number of pedestal are free to cross-talk the number of each p.e is assumed to be follow the Poisson distribution The number of 1p.e : P(1) ( estimated by pedestal ) || without cross-talk The number of 1p.e : P(1) ( measured ) || with cross-talk This difference corresponds to the decrease by cross-talk. measurement

17 Cross-talk rate Cross-talk rate at operation voltage defined by HPK is about 20% at 20degree. ( We measured within the wider range about bias voltage. ) 10% 50% Cross-talk rate 400pixel Cross-talk rate 100pixel 10% 50% Bias voltage [V] Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree

18 Cross-talk rate Cross-talk rate is a function of  V. 10% 50% 12 Delta V Cross-talk rate 400pixelCross-talk rate 100pixel 10% 50% Blue: 15degree Green: 20degree Red: 25degree VV VV

19 Photon Detection Efficiency Photon Detection Efficiency ( = PDE ) is defined as this equation. PDE consists of three elements. Geometrical Efficiency. A ratio of active area to total area (50%~70%) Quantum Efficiency of active area (60~80%) Probability of Geiger discharge (60~90%) Depending on MPPC type Depending on wavelength of injected light Depending on bias V MPPC have the highest QE in Green light.

20 relative PDE measurement ・ only the light going through 1mmφslit is detected. ・ The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC. MPPC 1mmφslit Blue LED ( total area 1mm 2 ) PMT PMT made by HPK, type H8643 set up Moving stage

21 relative PDE PDE is about 2~3 times higher than that of PMT. 1 2 Relative PDE 400pixelRelative PDE 100pixel Bias voltage [V] Bias voltage [V] Blue: 15degree Green: 20degree Red: 25degree

22 relative PDE PDE is a function of Delta V. 1 2 Relative PDE 400pixelRelative PDE 100pixel Blue: 15degree Green: 20degree Red: 25degree VV VV

23 Linearity The linearity become those equation. MPPC have the fixed number of pixel ( 100pixel, 400pixel,… ) MPPC is non-linear device when the number of injected photons is not small compared to pixel number.

24 Linearity The green line shows the expectation value calculated from number of pixels. Blue: DATA plot Green: expectation Linearity 400pixel Injected photoelectron per pixel Fired pixel [ % ] MPPC can operate as linear device. ~25p.e about 100pixel type ~100p.e about 400pixel type. linear Linearity 100pixel Fired pixel [ % ] Injected photoelectron per pixel linear 25% Blue: DATA plot Green: expectation

25 LASER test (using KEK-DTP LASER system)

26 Laser test at KEK, Japan Motivation ・ study the response of each pixel of MPPC Uniformity within 1pixel Uniformity in each pixel Feed back this information to HPK microscope Laser source λ=825nm width 50ps Moving stage 1μm pitch (x, y) Laser spot size ≒ 10μm Picture of microscope MPPC 100μm Uniformity… gain cross-talk rate efficiency

27 RMS/mean=2% 0.25 Uniformity within 1pixel 100pixel efficiency GAIN Cross talk rate Response within 1 pixels is uniform Efficiency, Gain (in sensitive region) High at edge of sensitive region When the avalanche occur at edge of pixel, it is easy to emit to the next pixel (this is cross-talk). Cross-talk rate (in sensitive region) Sensitive region

28 RMS/mean=3% Uniformity of each pixel 100pixel efficiency GAIN Response of each pixel is uniform

29 Summary MPPC has good performance ! 100pixel400pixel Gain Noise rate(1p.e) [ kHz ] Cross-talk rate PDE Uniformity within 1 pixel of each pixel Uniform(2~3%)

30 Supplements

31 MPPC ceramic package for T2K This ceramic package make their alignment by the out side frame.

32 The principle of operation of 1APD pixel APD (Avalanche Photo Diode) is a photo-diode that amplify the signal by operating the electron avalanche, that occur on the regions of pn- connection with high electric field. This high electric field is formed by applying bias voltage oppositely. p+p+ absorption regionpn E γ e-e- hole When the bias voltage exceed the threshold voltage ( that is named “Break Down Voltage” ), very little light can make APD to occur the electrical discharge. This amplify is become about 10 6, and the height of signal doesn’t relate to the number of injected photon. We can know only “the photon has come” or “not”. GND V+V+ Amplifying by electron avalanche

33 Temperature dependent of V BD VBD [V] 100pixel400pixel 25degree degree degree The results become linear.

34 Set up for measuring linearity set up MPPC The number of photons emitted to MPPC are monitored by PMT. PMT Paper ( to shade off LED light )

35 RMS/mean=1.7% RMS/mean=1.6% Uniformity within 1pixel pixel efficiency GAIN Cross talk rate

36 RMS/mean=2.9% RMS/mean=3.4% Uniformity of each pixel pixel efficiency GAIN Cross talk rate