High visibility pump reconstruction via ultra broadband sum frequency mixing of intense phase-conjugated twin beams.

In this paper we show how after the generation of parametric down-conversion radiation (PDC) in the very high gain pulsed regime, we are able to reconstruct the pump via up-conversion of the twin beams originated from that PDC process. The peculiarity of the experiment is the ultra-broad spectral and angular bandwidth sent into the process of sum frequency mixing thanks to an achromatic imaging technique from the exit face of the PDC crystal using off-axis parabolic mirrors. The recorded spectra presented illustrate the high visibility recombination of the intense phase-conjugated signal and idler beams and pave the way for the investigation of both the spatial and temporal properties of the near field biphoton amplitude.

Measurement of sub-shot-noise correlations of spatial fluctuations in the photon-counting regime.

We have measured sub-shot-noise quantum correlations of spatial fluctuations in the far-field image of the parametric fluorescence created in a type I beta-barium-borate nonlinear crystal. Imaging is performed at very low light level (0.15 photons per pixel) with an electron multiplying charge coupled device camera. Experimental results overcome the standard quantum limit shot-noise level without subtraction of the variance of the detection noise.

Effective signal-to-noise ratio improvement by parametric image amplification.

We show experimentally that parametric optical preamplification greatly improves the signal-to-noise ratio of an image if the detector has a poor quantum efficiency and/or a great level of readout noise. Results are fully consistent with the theory of quantum-noise-limited amplification.