Transforming a spatially coherent light beam into a diffused beam of small diffusion angle using suitable surface scattering

Imposing a phase random distribution in an interval larger than 2π on a spatially coherent light beam transforms the beam into a diffuse one. However, if the required random phase distribution is imposed by a rough transparent plate immersed in a transparent liquid or covered by another transparent material of refractive index close to that of the plate, the diffused light is confined in a small cone around the light incident angle. This renders to fabricate diffusers with high transmission efficiency that has applications in computer displays, bar code scanners, and image forming systems including conventional optical microscopes.