Effects of illumination wavelength and diffuser roughness height on speckle formation and phase retrieval
Abstract
We investigate the influences of the illumination beam wavelength and diffuser roughness height on the speckle intensity measurements and the performance of the speckle-based phase retrieval technique. Two illumination sources are considered: Helium Neon laser (632 nm, red) and laser diode [808 nm, infrared (IR)]. Using a particular diffusing element, IR illumination resulted in higher speckle contrast and significant axial intensity variation compared to the case of red illumination. As a result, enhanced phase maps are retrieved under the IR illumination. This study shows that the speckle-based phase retrieval technique, with a suitable diffusing element, may be extended to non-optical wavelengths such as x-ray and deep ultraviolet wavelengths.