Numerical investigation of the nonlinear dynamics of a hybrid acousto-optic Bragg cell with a variable feedback gain
The purpose of this thesis is to retrieve the three-dimensional amplitude and phase of objects using a noninterferometric intensity-based method of phase retrieval called transport of intensity. The phase on the detector plane is found by recording the intensity profiles at two neighboring distances of propagation and numerically solving both general and simplified formats of the transport of intensity equation using the fast Fourier transform. The intensity and phase information on the observation plane is then used to reconstruct the original amplitude and phase of the object, using numerical back-propagation. Both amplitude and phase objects are considered. For amplitude objects, tomography using multiplicative technique is used to reconstruct the true three dimensional shape of the object. This is done both for simulated amplitude objects, where the optical fields are numerically propagated to the observation plane, as well as experimentally, where a physical object is illuminated by a laser and the diffracted intensities registered by CCD cameras around the observation plane. It is shown that transport of intensity is well suited for moving objects. Two examples of imaged phase objects are considered. The first is the induced phase in a liquid due to heating by a focused laser beam. The second is the induced phase in a photorefractive material during two-wave mixing. In both cases, the induced phase is reconstructed using transport of intensity.