Abstract
Electron-bombarded pixel image sensors, where a single photoelectron is accelerated directly into a CCD or CMOS sensor, allow wide-field imaging at extremely low light levels as they are sensitive enough to detect single photons. This technology allows the detection of up to hundreds or thousands of photon events per frame, depending on the sensor size, and photon event centroiding can be employed to recover resolution lost in the detection process. Unlike photon events from electron-multiplying sensors, the photon events from electron-bombarded sensors have a narrow, acceleration-voltage-dependent pulse height distribution. Thus a gain voltage sweep during exposure in an electron-bombarded sensor could allow photon arrival time determination from the pulse height with sub-frame exposure time resolution. We give a brief overview of our work with electron-bombarded pixel image sensor technology and recent developments in this field for single photon counting imaging, and examples of some applications.
Highlights
Photon counting imaging is a well-established low light level imaging technique where an image is assembled from individual photons whose position is recorded during the detection process, usually with a position-sensitive sensor
Point detectors (HPDs) are often combined with TCSPC timing electronics based on a time-to-amplitude converter (TAC) and used for photon arrival timing, for example, in fluorescence lifetime imaging scanning fluorescence microscopy [21,22], but with pixel image sensors photon arrival timing is less straightforward
Single photon events detected with EBCMOS cameras are reported to be very similar to EBCCD photon events
Summary
Photon counting imaging is a well-established low light level imaging technique where an image is assembled from individual photons whose position is recorded during the detection process, usually with a position-sensitive sensor (i.e., a camera). The advantages of EB sensors over intensified camera systems include reduced sensor size and weight, increased sensitivity and dynamic range, faster response time, and better contrast and resolution They require a high voltage of several kV between the photocathode and the CCD sensor in vacuum, and backscattered photoelectrons can be detected on the low energy side of the pulseheight distribution, making it asymmetric [20]. We note here that recent developments in single photon avalanche diode (SPAD) detectors, which can be manufactured in large arrays using CMOS technology, show great promise as an alternative to vacuum-based detector technology They simultaneously deliver single photon sensitivity and picosecond timing resolution in tens of thousands of pixels, and have the potential to significantly advance time-resolved fluorescence microscopy and other fields, see Section 5 for more details
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