Young's Diagnostics of Phase Singularities into Polychromatic Light Fields

Abstract

Two original approaches for the diagnostics of phase singularities (such as optical vortices, screw dislocations of a wave front) based on the Young-Rubinowicz mOdel of diffraction phenomena are represented. Both techniques are implemented without using a separate reference wave, as in common interference techniques. That is why they are very convenient for analysis of spatially coherent polychromatic fields. The first technique is based on the use of an opaque strip as the diffraction device. Bending Young's interference fringes produced by the edge diffraction waves from two rims of the strip within the geometrical shadow region reflect helicity of a wave front, so that the direction and magnitude of bending correspond directly to the sign and the modulus of topological charge of the optical vortex, respectively. This technique is practicable for diagnostics of isolated polychromatic vortices, such as rainbow Laguerre-Gaussian mode, where the condition of mutual spectral purity is satisfied. Another technique is based on the use of knife-edge diffraction. The edge of an opaque screen serves as the source of a reference wave, which interferes with the tested field within the directly illuminated region. One observes typical interference forklets near the geometrical shadow boundary, which detect optical vortices. This technique is more applicable to diagnostics of phase singularities in polychromatic speckle fields due to the condition of mutual spectral purity is satisfied automatically.