Detectivity optimization to detect of ultraweak light fluxes with an EM-CCD as binary photon counter array

For a wide range of purposes, one faces the challenge to detect light from extremely faint and spatially extended sources. In such cases, detector noises dominate over the photon noise of the source, and quantum detectors in photon counting mode are generally the best option. Here, we combine a statistical model with an in-depth analysis of detector noises and calibration experiments, and we show that visible light can be detected with an electron-multiplying charge-coupled devices (EM-CCD) with a signal-to-noise ratio (SNR) of 3 for fluxes less than 30 photon s- 1 cm- 2. For green photons, this corresponds to 12 aW cm- 2 X 9 x 10- 11 lux, i.e. 15 orders of magnitude less than typical daylight. The strong nonlinearity of the SNR with the sampling time leads to a dynamic range of detection of 4 orders of magnitude. To detect possibly varying light fluxes, we operate in conditions of maximal detectivity D rather than maximal SNR. Given the quantum efficiency QE(lambda) of the detector, we find D = 0.015 photon- 1 s(1/2) cm, and a non-negligible sensitivity to blackbody radiation for T > 50 degrees C. This work should help design highly sensitive luminescence detection methods and develop experiments to explore dynamic phenomena involving ultra-weak luminescence in biology, chemistry, and material sciences