Three-dimensional coherence of light speckles: Experiment

We provide an experimental detailed study of the three-dimensional coherence properties of light speckles produced by different tunable pseudothermal sources. Our findings confirm the theoretical prediction of the companion article, according to which the longitudinal coherence of the speckles is ruled by ordinary diffraction laws only in the deep-Fresnel zone close to the source, deviates from this behavior in the Fresnel zone, and tends to become infinite when approaching the Fraunhofer zone. A quantitative comparison with theory is presented for Gaussian speckles in all the three regimes and for Airy speckles in the deep-Fresnel zone. Potential applications to three-dimensional imaging techniques are briefly discussed. © 2009 The American Physical Society.