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9 May 2012 Shot-noise-limited imaging based on N-photon detection
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We present the use and characterization of a Single Photon Avalanche Detector (SPAD) for shot-noise-limited imaging at ultra-low light-level. Many demanding photonic applications, such as fluorescence laser scanning microscopy, require the acquisition of very weak optical signals, generally composed by few photons mostly in the visible and near infrared wavelength. Conventional photo detector that utilizes analog current integration is generally not able to detect such low intensity signal due to the excessive noise at low signal levels. In this paper, we demonstrate shot-noise-limited imaging by scanning and using N-photon photo-detection implemented with a Single Photon Avalanche Detector. We choose a LabView based approach, extending the methods of N-photon photo-detection. In our implement, the number of TTL pulses received from the Single Photon Avalanche Detector within the duration of the pixel dwell time is recorder by a LabView pre-programmed instrument and then wrote into a pre-allocated image array, using the pixel clock and line sync signals to determine the position within the image. Experiments show that our N-photon photo-detection exhibits extreme sensitivity even down to single photon level. This characteristic of the ultra-sensitivity makes this scheme very suitable for low signal levels in fluorescence laser scanning microscopy. Related with the dynamic range, the maximum count rate of our N-photon photo-detection scheme reaches 106 counts per second (cps) while maintaining high detection efficiency. It has also been demonstrated that the thermoelectrically cooled Single Photon Avalanche Detector neutralizes dark counting noise of detector and thus obtain a nearly shot-noise-limited imaging performance.
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Wei-ji He, Yaojin Chen, Qian Chen, Guo-Hua Gu, and Wei Cheng "Shot-noise-limited imaging based on N-photon detection", Proc. SPIE 8366, Advanced Environmental, Chemical, and Biological Sensing Technologies IX, 83660T (9 May 2012);

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