Abstract
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.
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The movie displays the sequence of 21 spatial intensity correlation maps, from Gi,231 to Gi,251 (abscissas: i=1 to 96). In the upper part of each frame (j=128 to 255, region of PFT) the 8 bit gray scale covers the correlation values from 0.55 to 1. Value 1 is only achieved by the auto-correlated pixel. In the lower part of each frame (j=0 to 127, region of PIM) the 8 bit gray scale covers the correlation values from 0 to 0.45. The single marker, in green, tracks the auto-correlated pixel and moves from j=231 to 251 at a speed which is 3/4 the speed at which the couple of red markers moves. Note that the red markers remain synchronous with the slit images. Enlarged views of Gi,242, Gi,243, Gi,244 and Gi,245 (with i=64) are displayed in Fig. 6 in the Appendix
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42.65.Lm; 42.30.Va; 42.50.Ar
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License ( https://creativecommons.org/licenses/by-nc/2.0 ), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Andreoni, A., Puddu, E. & Bondani, M. Parallel spatial intensity correlations to decode random frequency-downconverted images. Appl. Phys. B 85, 125–129 (2006). https://doi.org/10.1007/s00340-006-2324-9
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DOI: https://doi.org/10.1007/s00340-006-2324-9