What is MPPC ?
The MPPC (multi-pixel photon counter) is one of the devices called SiPM (silicon photomultiplier). It is a new type of photon-counting device using multiple APD (avalanche photodiode) pixels operating in Geiger mode. Although the MPPC is essentially an opto-semiconductor device, it has an excellent photon-counting capability and can be used in various applications for detecting extremely weak light at the photon counting level. The MPPC operates on a low voltage and features a high multiplication ratio (gain), high photon detection efficiency, fast response, excellent time resolution, and wide spectral response range, so it delivers the high-performance level needed for photon counting. The MPPC is also immune to magnetic fields, highly resistant to mechanical shocks, and will not suffer from “burn-in” by incident light saturation, which are advantages unique to solid-state devices. The MPPC therefore has a potential for replacing conventional detectors used in photon counting up to now. The MPPC is a high performance, easy-to-operate detector that is proving itself useful in a wide range of applications and fields including medical diagnosis, academic research, and measurements.
How to use
The MPPC characteristics greatly vary depending on the operating voltage and ambient temperature. In general, raising the operating voltage increases the electric field inside the MPPC and so improves the gain, photon detection efficiency, and time resolution. On the other hand, this also increases unwanted components such as dark count, afterpulses, and crosstalk which lower the S/N. The operating voltage must be carefully set in order to obtain the desired characteristics.
The MPPC can be used by various methods according to the application. Here we introduce a typical method for observing light pulses. Using a wide-band amplifier and oscilloscope makes this measurement easy. Figure shows one example of a connection to a wide-band amplifier. The 10 Ω resistor and 0.1 μF capacitor on the power supply portion serve as a low-pass filter that eliminates high-frequency noise of the power supply. The 10 Ω resistor is also a protective resistor against excessive current.
The MPPC itself is a low-light-level detector, however, in cases where a large amount of light enters the MPPC, for example, when it is coupled to a scintillator to detect radiation, a large current flows into the MPPC. This may cause a significant voltage drop across the protective resistor, so the protective resistor value must be carefully selected according to the application. The amplifier should be connected as close to the MPPC as possible.
Distance measurement (LIDAR)
MPPC can be used for distance measurement applications using the TOF method such as in-vehicle LIDARs, hand-held rangefinders, and human body sensors.
PET (positron emission tomography)
MPPCs that are arranged 360° around an object detect pair annihilation gamma rays, and the location of a target, such as cancer, can be determined on the basis of the detected intersections.
To detect the type, quantity, and nucleic acid (DNA, RNA), etc. of cells, laser light is incident on a fast running solution containing the cells. This enables the MPPC to capture the minute fluorescence that is emitted.
The MPPC module can detect minute fluorescence emission of reagents.
When a laser is made to pass through a chamber that contains a gas or liquid, the quantity and size distributions of the particles in the chamber can be determined through the detection of the light that is scattered by the particles.
Scanning laser ophthalmoscope (SLO)
In ophthalmoscopy, for safety reasons the light that is irradiated into the eyeball must have a low intensity. MPPC and APD modules can be used to detect faint reflected light from the eye with superior resolution and contrast.