Video Tutorials:
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2018:
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E. Fisher, "Single-Photon Detection Using Avalanche Gain in Silicon", 15-minute IEEE TV Video, IEEE Instrumentation and Measurement Society (IEEE-IMS) Video Tutorials: Expert Series
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Abstract: Often in metrology, we wish to detect extremely low magnitude optical signals, but how do we go about achieving this? Photodiodes (PDs) use the “internal photoelectric effect”, which will be briefly discussed, however, to detect single photons we can use the avalanche or impact ionisation effect. Linear avalanche gain devices such as avalanche photodiodes (APDs) give some gain and are useful to give a continuous time analogue output, but if we allow the avalanche to run-away, the breakdown of a photodiode’s p-n junction can produce a gain in excess of 10^6 with a digital output suitable for direct connection to signal processing logic. We call these devices single-photon avalanche diodes (SPADs), which can be implemented as large arrays (10s of thousands) and are key enabling technologies for time of flight (ToF) 3D imaging, light detection and ranging (LIDAR) and solid-state single-photon detectors (called silicon photomultipliers or Si-PMs) that can replace the traditional photo-multiplier tube (PMT). In this video tutorial, we quickly review what the photon is and its detection mechanisms, namely the photoelectric effect as opposed to Compton Scattering or Pair Production. We then quickly discuss avalanche gain and SPADs, mentioning a few of the advantages of these devices and their limiting factors. SPADs have now been used for biological metrology applications including fluorescence lifetime imaging microscopy (FLIM), along with low-light optical communications. Their introduction into CMOS in the early 2000s represents a step increase in the functionality and logic complexity we can achieve with arrays of these devices.
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[This was my first video tutorial delivered to the camera only - strangely this is more difficult than a room full of people]
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