ABSTRACT
Small-angle, noncollinear, first- and second-order interferometric autocorrelation experiments with Ti:sapphire laser pulses of 9-80-fs duration have been performed with microaxicon arrays. Predictions of short-pulse spatial frequency effects were verified by comparison of interference patterns of single elements and matrices. An angular spectrum of Gaussian-shaped axicons was analyzed on the basis of linear refraction. Experimental data indicate contributions to autocorrelation by nonlinear refraction and travel-time differences. The influence of the spectral bandwidth was separated from the pulse-duration-dependent effects. Spatially resolved information about the coherence time was delivered by the multichannel structure.
ABSTRACT
Multiple quasi-Bessel beams are generated by transmission of sub-30-fs pulses from a Ti:sapphire laser through refractive thin-film microaxicon arrays. Time-integrated intensity distributions at several axial positions and for pulse durations of 26 and 12.5 fs reveal significant changes of contrast, envelope function, and spatial frequency spectrum in comparison with continuous wave data. Evidence is presented that strong space-time coupling results in a time-dependent interference zone.
ABSTRACT
Advantages of the lensless Fourier holography setup for the reconstruction of digitally recorded holograms in holographic interferometry are presented. This very simple setup helps to achieve a maximum lateral resolution of the object under investigation. Also, the numerical-reconstruction algorithm is very simple and fast to compute. A mathematical model based on Fourier optics is used to describe discretization effects and to determine the lateral resolution. The recording and the reconstruction processes are regarded as an optical imaging system, and the point-spread function is calculated. Results are verified by an experimental setup for a combined shape and deformation measurement.
ABSTRACT
A neural network approach for the automatic detection of defects by evaluation of holographic interference patterns of the loaded technical components is described. Translation- as well as rotation-invariant features are defined based on the maximal local slope of the intensity and a partition of the interference pattern into nonoverlapping areas. The training sample set is generated by computer simulation of interferograms directed by a few typical experimentally measured samples. Practical results show the feasibility of the method. A strategy for application of neural networks to any holographic nondestructive testing task is outlined.
ABSTRACT
We present a new method for displaying light in flight. Fresnel holograms are recorded directly on a CCD sensor, electronically stored, and numerically reconstructed. Experimental results are shown. From different parts of a single holographic recording, different views of a wave front can be reconstructed. This means that the temporal evolution of a wave front can be observed by numerical methods.
ABSTRACT
The principle of recording holograms directly on a CCD target is described. A real image of the object is reconstructed from the digitally sampled hologram by means of numerical methods.
ABSTRACT
The fundamentals of digital recording and mathematical reconstruction of Fresnel holograms are described. The object is recorded in two different states, and the holograms are stored electronically with a charge-coupled-device detector. In the process of reconstruction the digitally sampled holograms are applied to the different coherent optical methods as hologram interferometry and shearography. If the holograms are superimposed and reconstructed jointly, a holographic interferogram results. If a shearing is introduced in the reconstruction process, a shearogram results. This means that the evaluation technique, e.g., hologram interferometry or shearography, can be influenced by numerical methods.
ABSTRACT
Holographic interferometry with a reference beam reflected out of the object illumination beam by a small mirror fixed to the object compensates statistical vibrations and object motions caused by rough environments and yields stable interference patterns with sufficient contrast. Based on theoretical investigations of the fringe formation in this case, methods for determining the object motion and deformation are developed. It is shown that zero-order fringes always pass the reference mirror in the reconstructed holographic image when this method is used. The displacement of the reference mirror is determined by an additional object undergoing no motion between the two exposures of a double-exposure hologram.
