Image formation by inversion of scattered field data: experiments and computational simulation.

The 3-D scattering potential of microscopic objects is reconstructed as well as the 2-D equivalent object from amplitude and phase data of the scattered field. The experimental setup and results are presented and discussed alongside corresponding computer simulations. In the computational simulation, several small coated spheres were assumed, and the scatter field data were determined by the Mie diffraction theory. In the experiment, a small sphere of 40-microm diam was used, and the scattered field was measured by interferometric methods. Two alternative methods were used to record the scattered field data; their sensitivity to phase quantization is discussed. Since in the experimental situation the scattered field data can only be determined in a very restricted range, a distinct smear of the PSF of this imaging process results. We describe the consequences of this drawback in terms of this PSF. On the other hand, we show that this allows a reduction of computation time in the digital inversion of the scattered field data.