1,833 research outputs found
Optical memory disks in optical information processing
We describe the use of optical memory disks as elements in optical information processing architectures. The optical disk is an optical memory devicew ith a storage capacity approaching 1010b its which is naturally suited to parallel access. We discuss optical disk characteristics which are important in optical computing systems such as contrast, diffraction efficiency, and phase uniformity. We describe techniques for holographic storage on optical disks and present reconstructions of several types of computer-generated holograms. Various optical information processing architectures are described for applications such as database retrieval, neural network implementation, and image correlation. Selected systems are experimentally demonstrated
Comparison of beam generation techniques using a phase only spatial light modulator
Whether in art or for QR codes, images have proven to be
both powerful and efficient carriers of information. Spatial light modulators
allow an unprecedented level of control over the generation of optical fields
by using digital holograms. There is no unique way of obtaining a desired
light pattern however, leaving many competing methods for hologram
generation. In this paper, we test six hologram generation techniques
in the creation of a variety of modes as well as a photographic image:
rating the methods according to obtained mode quality and power. All
techniques compensate for a non-uniform mode profile of the input laser
and incorporate amplitude scaling. We find that all methods perform well
and stress the importance of appropriate spatial filtering. We expect these
results to be of interest to those working in the contexts of microscopy,
optical trapping or quantum image creation
Holographic optical elements: Fabrication and testing
The basic properties and use of holographic optical elements were investigated to design and construct wide-angle, Fourier-transform holographic optical systems for use in a Bragg-effect optical memory. The performance characteristics are described along with the construction of the holographic system
Photolithographic fabrication method of computer-generated holographic interferograms
We consider the fabrication of high-quality interferogram-type diffractive optical elements with conventional photolithographic techniques and compare the results with those achievable with electron-beam lithography. The fringes associated with the phase transfer function of the binary phase holographic interferogram are approximated with rectangles, which can be realized at submicron accuracy using a pattern generator and step-and-repeat camera. The effects of the rectangle quantization are analyzed both numerically and experimentally with the aid of diffraction patterns produced by simple focusing elements. Both resolution and diffraction efficiency of the best holograms approach their theoretical values
Shaping electron beams for the generation of innovative measurements in the (S)TEM
In TEM, a typical goal consists of making a small electron probe in the
sample plane in order to obtain high spatial resolution in scanning
transmission electron microscopy. In order to do so, the phase of the electron
wave is corrected to resemble a spherical wave compensating for aberrations in
the magnetic lenses. In this contribution we discuss the advantage of changing
the phase of an electron wave in a specific way in order to obtain
fundamentally different electron probes opening up new application in the
(S)TEM. We focus on electron vortex states as a specific family of waves with
an azimuthal phase signature and discuss their properties, production and
applications. The concepts presented here are rather general and also different
classes of probes can be obtained in a similar fashion showing that electron
probes can be tuned to optimise a specific measurement or interaction
Laser microsculpting for the generation of robust diffractive security markings on the surface of metals
AbstractWe report the development of a laser-based process for the direct writing (‘microsculpting’) of unique security markings (reflective phase holograms) on the surface of metals. In contrast to the common approaches used for unique marking of the metal products and components, e.g., polymer holographic stickers which are attached to metals as an adhesive tape, our process enables the generation of the security markings directly onto the metal surface and thus overcomes the problems with tampering and biocompatibility which are typical drawbacks of holographic stickers. The process uses 35ns laser pulses of wavelength 355nm to generate optically-smooth deformations on the metal surface using a localised laser melting process. Security markings (holographic structures) on 304-grade stainless steel surface are fabricated, and their resulted optical performance is tested using a He–Ne laser beam of 632.8nm wavelength
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