Digital holography has a limited possibility to reconstruct object details because of an insufficient pixel number of
commercially available CCD cameras. Software hologram apodization introduces an additional damping of registered
object information and, in general, it can be considered as a disadvantageous process. However, for the reconstruction
of phase objects in digital holography the unwrapping procedures are indispensable. Moreover, for surfaces with
considerable roughness depth there are large phase changes between neighbor CCD camera pixels. Therefore
unwrapping procedures can introduce essential errors to reconstructed phase images. In the paper, besides general
considerations on the apodization in digital holography, experimental and computer simulation results of the hologram
apodization for surface shape measurements are presented.
Beamsplitter is a crucial element of the Fourier spectrometer. In conventional form it is composed of two identical wedge plates reducing ghost reflections influence. Simultaneously, it can introduce the most significant spectrum errors in the reason of improper quality or misalignment. The influence of geometrical parameters of both wedge plates on measured spectrum is presented. The paper contains numerical analyses for assumed and real object spectrum. Additionally the dependence between incident wave shape and quality of reconstructed spectrum is considered.
Significant progress in MEMS/MOEMS development requires new measurement methods. The pulse interferometry is one of the widely used technique for oscillating object analyses. It is based on object observation during the short laser pulse illumination. In the paper a new method for electronic time synchronization of oscillating objects, laser pulses and camera registration is proposed. The system is developed to measure the silicon micromembrane surface shape. Laser pulse mode properties and camera adaptation to a microinterferometer setup are considered in the paper. A complementary system oriented on the investigation of the relationship between object transient shape changes and oscillation phases is shown. Preliminary results of measurement of silicon membrane shape changes during oscillations are presented.
In digital holography the imaging process consists of physical registration using CCD camera and digital image reconstruction with specialized software. Amplitude gradients of the reconstruction field at the hologram plane influence significantly the phase reconstruction quality. The field truncation by hologram edges is of particular concern. The image reconstruction process can be software repeated several times using various apodization functions. Basing on phase imaging changes introduced by different apodization functions a decrease of phase errors can be achieved for some object types. Basing on the results received from experimental measurements and computer simulations for some object examples the advantages and disadvantages of the proposed method will be presented.