Parallel spatial intensity correlations to decode random frequency-downconverted images

We record frequency-downconverted images that are chaotic, as they are obtained in a χ⁽²⁾ crystal from the interaction of two pulsed pseudo-thermal fields of which the one at the higher frequency encountered the imaged object. Spatial correlations of the intensity fluctuations in these chaotic images with the intensity of a single spatial Fourier component of the low-frequency input field, allow image retrieval if the number of records on which the ensemble-averages are calculated is suitably large. When it is too small to achieve a satisfactory result, we show that computing the correlations in parallel with different components of the low-frequency input field, shifting the correlation maps according to a rule suggested by 3D phase-matching, and averaging them, leads to the recovery of the downconverted image. The method can be used for secure and fast image transmission. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.PACS 42.65.Lm; 42.30.Va; 42.50.Ar