Tuesday marked the final nail in the coffin of my MPhys research year at the Rutherford Appleton Laboratory. As I’ve previously mentioned, I worked at the CMOS Sensor Design Group there and… didn’t have a very easy time. Nevertheless, I’ve come out of it confident in my ability to produce good research. For me, the next step is further study in the area of Photonics, leading to a PhD in the area.

Back on topic: on Tuesday I presented a short talk on the subject of the research I undertook at RAL. Since it was only 15 minutes and aimed at second year undergraduate Physicists, I wasn’t able to cover everything I’d have liked to. I think, however, that I gave a reasonable account of Single Photon Avalanche Diodes and dead time effects – that was the meat of the work suitable for actual publication. I was pleased at how it was received, but disappointed that I didn’t get harder questions.

Finishing the whole ordeal and being free is nice, but I can’t help thinking of returning to the subject for a kind of encore. There aren’t very many easy ways of learning about SPADs, so my intention is to try to produce a “Rough Guide To SPADs” type thing. I am going to proceed by sketching out the subject areas I’d like to cover.

Diodes, Image Sensors, Single Photon Counters

An introduction of sorts; the important principles of what a SPAD is.

SPADs in “Contrast” to Other Imagers

AKA: “But why can’t we use a Photomultiplier Tube?”

What a SPAD “Looks Like”

How to tell a SPAD from a spud from an APD.

SPAD Fundamentals – Analogies and Pictures

The bit where I explain how SPADs actually work. More or less.

Quenching, Reset, and SPAD Outputs

Why SPADs don’t break, and why you never get a “perfect” SPAD.

Practical SPADs – Important Parameters

How SPADs are set up and what to measure to test how good they are.

The Efficiency Problem

AKA: “Why you really do need conventions in engineering”.

The Photon Transfer Curve

A short description of one potential (general) solution to “The Efficiency Problem” and a related experiment.

External Reset and Dead Time (1) – The Problem

Yo dawg. I herd you like problems, so I put a problem in your problem.

External Reset and Dead Time (2) – The Model

Solving while we solve.

External Reset and Dead Time (3) – The Experiment

Demonstrating that it works.


Hopefully where it’s all brought together.

My aim is to make all of the discussions in the above accessible and fun, to a certain extent. Ideally, I would like the whole series of articles to be accessible to a first year Physics undergraduate, but still satisfying to a Professor in Photonic Devices.


About stoove

A physicist, researcher, and gamesman. Likes to think about the mathematics and mechanics behind all sorts of different things, and writing up the thoughts for you to read. A competent programmer, enjoys public speaking and mechanical keyboards. Has opinions which might even change from time to time.
This entry was posted in General Science, Physics, Single Photon Avalanche Diodes, Things to Come and tagged , , , , , . Bookmark the permalink.

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