Single-photon detection and imaging with a 10-Hz repetitively pulsed ultrasensitive coherent amplifier

We report an experimental investigation of an ultrasensitive coherent amplifier (USCA) operated at a 10-Hz repetition rate. We measure its quantum-noise-limited sensitivity, amplification, and image resolution. The USCA consisted of two Nd:YAG amplifiers in series with a high-gain four-wave Brillouin mirror with SnCl(4) as the Brillouin medium. We measure a noise-equivalent-energy sensitivity of 1.96 x 10(-19) J/mode or 1 photon/mode at a quantum efficiency of 96%. The system has an overall optical gain of 2.5 x 10(13). With a version of the USCA equipped with an imaging lens system, we demonstrate the amplification and phase conjugation of entire images with a resolution of 164 microrad across a field of view of 4 mrad or 21 x 21 resolution elements. To our knowledge, this is the first demonstration of a repetitively pulsed USCA.