CMOS Sensors
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Our CMOS sensors will provide time-resolved data for use in fluorescence lifetime microscopy.
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Single photons do not possess much energy – just 314 x 10-21 J at a red wavelength of 633nm – yet this is enough  to trigger a cascade of electronic and digital events in the smart Single Photon Avalanche Diodes (SPADs) being developed by Professor Robert Henderson’s CMOS Sensors & Systems Group at the University of Edinburgh.

CMOS sensors are capable of performing image-processing tasks such as time-to-digital conversion, analog-to-digital conversion, histogramming and noise reduction giving the technology an edge over CCD sensors. Bunches of single photons can be counted using digital logic gates. SPAD detectors can be arranged as single-point sensors, or laid out in a 1D line sensor or 2D array (imager) format.

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Each photon can be used to start a tiny CMOS stopwatch, providing time-resolved data for use in fluorescence lifetime microscopy and time-of-flight detection applications.

Photons having different colours can be spread over a region in space by optical diffraction gratings, yielding the wavelength spectrum of the light. Once directed onto a SPAD array, the relative time of arrival of each photon of any given colour can then be measured. The RAI and RAII light sensors used in the Proteus project can be thought of therefore as arrays of wavelength-sensitive pixel-stopwatches.

Repeated triggering of these pixel-stopwatches enables the construction of time-resolved photon statistics at each wavelength. These statistics – in the form of wavelength-time histograms – can be calculated on-chip, leading to a tremendous advantage in terms of data compression and data acquisition rates.

This ‘system-on-a-chip’ design enables the rapid construction and analysis of time-resolved spectra arising from fluorescence, Raman scattering and other light scattering phenomena. The long-term objective is to combine the sensors with a confocal microscopy scanning system and lung endoscope capable of building time-resolved microscopic imagery of cells.