[OPTICAL REVIEW Vol. 5, No. 3 (1998) 129-137]

Longitudinal Correlation Properties of Speckles Produced by Ring-Slit Illumination

Makram IBRAHIM,1 Jun UOZUMI1,* and Toshimitsu ASAKURA2

1Research Institute for Electronic Science, Hokkaido University, Sapporo, Hokkaido, 060-0812 Japan, 2Faculty of Engineering, Hokkai-Gakuen University, Sapporo, Hokkaido, 064-0926 Japan

(Received November 20, 1997; Accepted March 11, 1998)

Spatial correlation properties are studied for speckle patterns produced in the diffraction region behind a lens which is located at a focal distance from a diffuser with an aperture under illumination of the coherent plane-wave light. It is shown theoretically that, if a ring-slit aperture of a negligible slit width is used, the speckle field produced has a perfect correlation in the longitudinal direction. An experiment was performed using a circular aperture and ring-slit apertures having different ratios of the inner to the outer radius and the speckle pattern produced using the ring-slit aperture with the smallest slit width had the longest longitudinal correlation in all cases examined. The statistical stationarity and symmetry of the speckle field, as well as variation in the speckle size, are also discussed.

Key words: Bessel beam, clustered speckles, longitudinal correlation, intensity correlation, ring slit