Speckle reduction by angle diversity using a translucent spatial light modulator

A translucent spatial light modulator (SLM) and a condenser lens are introduced to suppress the laser speckle effect. The SLM is programmed as a sinusoidal grating with rotating orientation and/or adjustable period. The incident laser beam is diffracted into various diffraction orders after the SLM modulation, and the diffraction light beams with temporally changing incident angles are focused onto a transmission diffuser by a condenser lens. A CCD camera is used to record the speckle patterns in free space, and the speckle effect is reduced after integrating all the speckle patterns together. The speckle reduction principles are discussed, and about 0.3 speckle contrast ratio (CR) is obtained, where the grating rotating orientation span is 5°, and two grating periods have been chosen.