Structure determination of weak phase objects from interferometric near-field measurements

Amplitude and phase of diffraction near fields behind two-dimensional weak phase objects (n ≍ 1.02 + iO.0002) are measured with electromagnetic 3-cm waves in TM and TE polarization. Dielectric slabs and strips with a trapezoidal or rectangular cross section are considered (width 1.5λ-36.0λ; thickness 0.6λ-2.4λ; wedge angle 30°-150°). For numerical simulation of the measured fields, a modification of the first Born approximation for weak scatterers is developed, which yields a remarkably better agreement with the measurements but requires no higher numerical efforts than the first Born approximation. Procedures for the determination of width, thickness, and wedge angle of the objects from measured diffraction fields are presented.