Analog single-photon counter for high-speed scanning microscopy.

We introduce a novel single-photon sensitive photodetection method of analog single-photon counting (SPC) for the application of high-speed scanning microscopy that requires high measurement speed and wide dynamic range for the photodetector. This scheme is based on analog electronic circuits which can perform proper differentiation and integration operations before and after discrimination of the analog signal from the photomultiplier tube (PMT), respectively. In spite of its simpler implementation, our analog SPC scheme exhibits good sensitivity and operation stability. Related with the dynamic range, the maximum count rate of our analog SPC is significantly improved due to the fast operation of the analog circuitry. This characteristic of the higher counting rate makes this scheme very suitable for high-speed scanning microscopy. It has also been demonstrated that the afterpulsing problem of an analog-mode PMT is the major noise source that degrades the image quality in the application of scanning microscopy, and our SPC scheme successfully neutralizes this kind of impulse noises to obtain a nearly shot-noise-limited imaging performance.