Development of Multi-Pixel Photon Counters (1) S.Gomi, T.Nakaya, M.Yokoyama, M.Taguchi, (Kyoto University) T.Nakadaira, K.Yoshimura, (KEK) for KEK-DTP photon sensor group Oct.31.2006 Hawaii

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)

Introduction

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

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

the MPPC is an excellent photon counting device 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( ~106 ), low bias voltage( ~70V ) Low-cost 6mm 5mm the MPPC is an excellent photon counting device We measured the basic performance of two kinds of MPPC, 100 pixel type, and 400 pixel type.

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

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

The gain can be estimated at intervals between 1p.e and the pedestal. Gain of MPPC is defined as this equation. Gain is measured by analyzing ADC distributions of MPPC signals. ADC distribution * STATUS DATA * 400 pixel MPPC BIAS : 70.0V / VBD =68.8V ( with PM AMP, ×102 ) 1p.e signal set up Measuring the little light from the blue LED by MPPC. Gain is measured by ADC distribution. blue LED MPPC 2p.e 3p.e pedestal 4p.e … The gain can be estimated at intervals between 1p.e and the pedestal.

Gain MPPC is a high gain device. Gain 100pixel Gain 400pixel 69 69.5 69.8 69.6 70 70.6 Bias voltage [V] Bias voltage [V] MPPC is a high gain device. Blue : 15degree Green : 20degree Red : 25degree From gain-voltage relation, the break down voltage can be measured. The break down voltage depends on the temperature.

Gain Gain is a function of DV. Gain 100pixel Gain 400pixel 0.2 1 1.6 0.8 1 2 2.4 DV DV Gain is a function of DV. Blue : 15degree Green : 20degree Red : 25degree

Noise signal of 100pixel MPPC at 25 degree. Noise rate MPPC is a noisy photo detector, so the noise rate is one of the important parameter to use actually. 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 . “ 1p.e noise ” 0.5 p.e = threshold “ 2p.e noise ” 1 p.e Noise signal of 100pixel MPPC at 25 degree. ( integrated ) 1.5 p.e = threshold

Noise rate 1p.e noise rate is about 100~400 kHz. Blue : 15degree Green : 20degree Red : 25degree Noise rate Noise rate [ MHz ] 100pixel Noise rate [ kHz ] 400pixel 400kHz 500kHz 1p.e 2p.e 1p.e noise 2p.e noise 100kHz 100kHz 69.1 69.5 70 69.2 70 70.4 Bias voltage [V] Bias voltage [V] 1p.e noise rate is about 100~400 kHz. 2p.e noise rate is about 0~200 kHz.

Noise rate Noise rate [ MHz ] 100pixel Noise rate [ kHz ] 400pixel 400kHz 500kHz 1p.e 2p.e 1p.e 2p.e 100kHz 100kHz 0.4 1 1.6 0.5 1 1.5 2 2.3 DV DV 1p.e noise rate is a function of both temperature and bias voltage. Blue : 15degree Green : 20degree Red : 25degree 2p.e noise rate seem to be a function of Delta V. This is due to “Cross-talk”.

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. Neighborhood pixel Avalanche g “ Cross-talk “ g

Cross-talk rate measurement The probability of cross-talk is estimated by the number of 1p.e . The number of pedestal are free to cross-talk measurement 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. The cross talk rate is determined.

Blue : 15degree Green : 20degree Red : 25degree Cross-talk rate Cross-talk rate 100pixel Cross-talk rate 400pixel 50% 50% 10% 10% 69 69.5 69.8 69.6 70 70.6 Bias voltage [V] Bias voltage [V] Cross-talk rate at operation voltage defined by Hamamatsu Photonics(HPK) is about 20% at 20degree. ( We measured within the wider range about bias voltage. )

Cross-talk rate Cross-talk rate is a function of Delta V. Cross-talk rate 100pixel Cross-talk rate 400pixel 50% 50% 10% 10% 0.2 1 1.6 0.8 1 2 2.4 1 2 Delta V DV DV Cross-talk rate is a function of Delta V. Blue : 15degree Green : 20degree Red : 25degree

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 (30%~70%) Quantum Efficiency of active area (60~80%) Probability of Geiger discharge (60~80%) Depending on MPPC type Depending on wavelength of injected light Depending on bias V MPPC have the highest QE in Green light.

relative PDE measurement ・only the light going through 1mmφslit is detected. set up Moving stage 1mmφslit ・The ratio of MPPC p.e to that of PMT p.e is taken as relative PDE of MPPC. PMT Blue LED MPPC ( total area 1mm2) PMT made by HPK, type H8643

relative PDE PDE is about 2~3 times higher than that of PMT. Relative PDE 100pixel Relative PDE 400pixel 3 2 2 1 1 69 69.5 69.8 69.6 70 70.6 Bias voltage [V] Bias voltage [V] Blue : 15degree Green : 20degree Red : 25degree PDE is about 2~3 times higher than that of PMT.

relative PDE Relative PDE is a function of Delta V. Relative PDE 100pixel Relative PDE 400pixel 3 2 2 1 1 0.2 1 1.6 0.8 1 2 2.4 DV DV Relative PDE is a function of Delta V. Blue : 15degree Green : 20degree Red : 25degree

MPPC have the fixed number of pixel Linearity 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. The linearity become those equation.

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

LASER test (using KEK-DTP LASER system)

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

Uniformity within 1pixel efficiency Sensitive region Uniformity within 1pixel Efficiency, Gain (in sensitive region) Cross-talk rate (in sensitive region) RMS/mean=2% 100pixel Response within 1 pixels is uniform 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 GAIN 0.25 RMS/mean=2%

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

Summary MPPC has good performance ! 100pixel 400pixel Gain Noise rate(1p.e) [ kHz ] Cross-talk rate PDE Uniformity within 1 pixel of each pixel uniform MPPC has good performance !

Supplements

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

Temperature dependent of VBD VBD [V] 100pixel 400pixel 25degree 68.80 68.83 20degree 68.52 68.51 15degree 68.25 68.20 The results become linear. ( measured by M.Taguchi, kyoto university )

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

Uniformity within 1pixel efficiency Uniformity within 1pixel 400pixel RMS/mean=1.7% Cross talk rate GAIN 0.25 RMS/mean=1.6%

Uniformity of each pixel efficiency Uniformity of each pixel RMS/mean=3.4% 400pixel Cross talk rate GAIN 0.18 RMS/mean=2.9%