Sensitive detection approaching 0.55 photon at 1064 nm using picosecond optical parametric amplifier

We present experimental investigation on detection approaching 0.55 photon per pulse at 1064 nm using a 1 kHz 355-nm pumped picosecond optical parametric amplifier (OPA) with uncooled ordinary Si-CCD. The gain factor of the OPA is measured to be ~5.75×107. The ultra-weak signal detection is achieved by significant improvement of the signal-to-noise ratio (SNR) of the OPA, which is realized by suppressing the superfluorescence background utilizing long distance detection and spatial filtering in the light path, and reducing the fluctuation of total output of the OPA with large sampling number of laser shots.