Speckle contrast for flat-topped field profiles

Speckle contrast is evaluated for flat-topped field profiles where the characterization and evaluation of speckle contrast are based on mathematical formulation and theoretical parameter variation. The speckle field which is represented by the random phase shift and the random phase tilt is multiplied by the flat-topped shaped field. The increase in the source size of the flat-topped field first causes the speckle contrast to increase, then reaches saturation. Increase in the variance of the phase shift of a flat-topped field causes an appreciable increase in the speckle contrast. Depending on the diffraction characteristics of the finite sized flat-topped field distribution, upon changing the variance of the phase shift, the speckle contrast exhibits different behavior at short and long propagation distances. However, especially for small variances of phase tilts, the speckle contrast seems to monotonically increase as the propagation distance becomes larger. The effect of the order of flatness on the speckle contrast is small at short propagation distances which can be appreciable at long propagation distances. (C) 2012 Elsevier Ltd. All rights reserved.