Screen solving problem of laser beam-projected image speckling by in-depth scattering

摘要

A new, greatly-simplified laser imaging device becomes possible, using an inexpensive screen (43). The screen, or a layer within it, includes light-scattering structures (50). Novelty centres on the thickness (d) of the screen or layer. This must exceed a critical thickness dkrit, measured in the direction of incidence of the image-forming laser beam. The critical thickness is calculated as a function of the mean spacing (b) of interference maxima, known and seen as speckling (52) and which are produced by the beam at the layer- or screen surface. The following relationship sets the lower limit of required thickness: d dkrit = b/(2(cos2 eta )). In this expression, (cos2 eta ) is the mean value of the square of the cosine of the scattering angle eta , of the characteristic scattering angle distribution, resulting from deflection of the laser beam at the structures (50).