Observation of singularities in multiply scattered microwave fields.

Speckle patterns of arbitrary resolution are obtained by applying the sampling theorem to measurements of two orthogonal components of the microwave field transmitted through multiply scattering samples. Core structures of phase singularities, phase critical points, and polarization singularities are explored. We find that equiphase lines connect phase singularities with opposite topological signs except for the bifurcation lines, which run through a phase saddle point, in agreement with predictions by Freund [Phys. Rev. E25, 2348 (1995)]. We observe hyperbolic equiphase lines near phase saddle points and elliptical equiphase lines around phase extrema. Polarization singularities of the vector field with the three morphologies predicted are observed.