Digital Gabor and off-axis particle holography by shaped beams: A numerical investigation with GLMT

In particle field holography, the laser beam is more or less astigmatic, and the particles are usually inhomogeneous. Holograms of homogeneous and multilayered spherical particles illuminated by shaped beam with Gabor and off-axis configurations in both near and far field are investigated on the basis of the generalized Lorenz-Mie theory (GLMT). Reconstruction of the simulated holograms are demonstrated using fractional Fourier transform. Effects of recording parameters, e.g. beam shape (circular or elliptical Gaussian beam) and particle location (before, at or after the beam waist) and inner refractive index gradient using multilayer model on the hologram pattern were evaluated. For the off-axis holography, special attentions are devoted to the Moiré effect reduction using a Gaussian beam as the reference wave and to the two series of concentric rings phenomenon using the Debye series. The code developed in this work enable to investigate the effects of the incident beam, reference wave, particle inner refractive index gradient, and CCD orientation on the formation and reconstructed image of the hologram separately.