Fresnel Zone Pattern Research Articles

Computational Optical Scanning Holography

Holographic techniques are indispensable tools for modern optical engineering. Over the past two decades, research about incoherent digital holography has continued to attract attention. Optical scanning holography (OSH) can obtain incoherent holograms using single-pixel detection and structured illumination with Fresnel zone patterns (FZPs). Particularly by changing the size of a detector, OSH can also obtain holograms under coherently illuminated conditions. Since 1979, OSH has continuously evolved. According to the evolution of semiconductor technology, spatial light modulators (SLMs) come to be useful for various imaging fields. By using SLM techniques for OSH, the practicality of OSH is improved. These SLM-based OSH methods are termed computational OSH (COSH). In this review, the configurations, recording and reconstruction methods, and proposed applications of COSH are reviewed.

All-optical dynamic focusing of light via coherent absorption in a plasmonic metasurface

Vision, microscopy, imaging, optical data projection and storage all depend on focusing of light. Dynamic focusing is conventionally achieved with mechanically reconfigurable lenses, spatial light modulators or microfluidics. Here we demonstrate that dynamic control of focusing can be achieved through coherent interaction of optical waves on a thin beam splitter. We use a nanostructured plasmonic metasurface of subwavelength thickness as the beam splitter, allowing operation in the regimes of coherent absorption and coherent transparency. Focusing of light resulting from illumination of the plasmonic metasurface with a Fresnel zone pattern is controlled by another patterned beam projected on the same metasurface. By altering the control pattern, its phase, or its intensity, we switch the lens function on and off, and alter the focal spot’s depth, diameter and intensity. Switching occurs as fast as the control beam is modulated and therefore tens of gigahertz modulation bandwidth is possible with electro-optical modulators, which is orders of magnitude faster than conventional dynamic focusing technologies.

Image reconstruction in an electro-holographic display

The optical phenomena arising in the process of forming reconstructed images in a hologram are explained and shown visually with the use of light field images. The light fields at different distances from the hologram on a DMD reveal that the reconstructed image of each object point is formed by the corresponding Fresnel zone pattern, which is reconstructed from the hologram when it is illuminated by a reconstruction laser beam. The reconstructed image is a circle of least confusion laden with noise and distortion. It has a finite size and does not appear at the object distance from the hologram due to the presence of aberrations, especially that of a strong astigmatism. The astigmatism appears along the direction of the rotating axis of each pixel and its cross at right angles. The aberrations and noise are responsible for the distortion and deterioration of the resolution in the reconstructed image, the difference of the image position from that of the object, and a reduction in the depth resolution. The light field images also reveal intensity fluctuations due to the addition of the in- and out-phase of the rays from the hologram.

Spatial coherence radar applied for tilted surface profilometry

A new method of spatial coherence profilometry is demon- strated. The surface profile is measured by shifting the spatial degree of coherence gradually in its own space of existence, and modulating its phase angle. In each point of the sample we analyze the change of light intensity versus the phase of a Fresnel zone pattern used as the intensity distribution of an incoherent quasimonochromatic source. The tilt of the surface is measured by gradually shifting the Fresnel zone plate on its transverse plane. This shift of the light source rotates the spatial degree of coherence around the coordinate origin until the condition of maximum interference visibility is fulfilled. The method works without any mechani- cal movement and a quasimonochromatic light illuminates the interfero- metric system. Experimental demonstration of the new method is pre- sented. © 2003 Society of Photo-Optical Instrumentation Engineers.

Three-dimensional remote sensing by optical scanning holography

A technique is presented by which holograms can be recorded when an object or scene is scanned with an optically heterodyned Fresnel zone pattern. The experimental setup, based on optical scanning holography, is described and experimental results are presented. We apply the scanning holography technique to three-dimensional reflective objects for the first time to our knowledge and address the unique requirements for such a system. We discuss holographic recording and numerical image reconstruction using a system point-spread function (PSF) approach. We demonstrate numerical image reconstruction of experimentally recorded holograms by two techniques: deconvolution with a simulated PSF and an experimentally acquired PSF.

23.4: A Liquid Crystal Fresnel Zone Device and Its Light Focusing Properties

AbstractA novel light‐focus device was fabricated and demonstrated. The device consists of two glass substrates and one liquid crystal (LC) layer. Each indium tin oxide electrode coated on the two inner substrate surfaces of the device was etched into Fresnel zone patterns. In field‐off state, the transmission is uniform and light is not focused. In field‐on state, a 2π phase difference between adjacent zones can be adjusted. Then the device becomes a Fresnel phase zone plate and acts as a lens. Moreover, for getting transmission independent of light polarization direction, the LC layer was treated by twist of 180° along the normal of substrate surfaces.

Twin-Image Noise Effects in Optical scanning Holography

In Optical Scanning Holography(OSH), 3-D holographic information of an object is generated by 2-D active optical scanning. The optical scanning beam can be a time-dependent Gaussian apodized Fresnel zone plate. In this technique, the holographic information manifests itself as an electric signal which can be sent to an electron-beam-addressed spatial light modulator for coherent image reconstruction. In this paper, we briefly review optical scanning holography and analyze the resolution achievable with the system. We also present mathmatical expressions of real and virtual images which are responsible for holographic image reconstruction. We then show the twin-image noise effect on the reconstruction in conjunction with the size of the Fresnel zone pattern through computer simulation.

Linear electronic scanning type of ultrasonic imaging system using comb electrode arrays with Fresnel zone pattern

A linear electronic scanning type of ultrasonic imaging technique using comb electrode arrays is described. The comb arrangement of electrodes is mounted on one surface of a thin piezoelectric ceramic plate, which makes the development of the scanning resolution easier in comparison with the use of conventional array transducer elements. The region between the comb electrode and the counter electrode operates as an equivalent thickness-mode vibrator. The comb electrode arrays are used to construct the Fresnel zone pattern. A longitudinal wave is effectively radiated into water via an acoustic lens. The point focusing of the sound beam is realized by the agreement of two orthogonal focal positions. We demonstrate ultrasonic imaging results for several samples using the present transducer.

A Simple Instrument for Measuring Image Steadiness in 16-mm Motion-Picture Cameras

Frame-to-frame image registration errors in a 16-mm cine camera can be measured directly by the moiré fringes formed by a double exposure of a Fresnel zone pattern target. A simple instrument incorporating a target and lens that attaches directly to the camera under test was designed and built. If the Fresnel zone pattern images are displaced with respect to one another, linear image registration errors are converted into angular motion of the fringes; it then becomes possible to separately analyze in-track and cross-track errors. The necessary displacement between exposures is provided by the rotation of an off-center target. The test film can be projected with a conventional projector and an estimate of the registration errors obtained, or the film can be analyzed with a low-power microscope or single-frame analytical projector. It will be most suitable for testing cameras in research, manufacturing, and repair.

Method and apparatus for producing acoustic waves by laser pulses

Focussed acoustic waves are generated free of physical contact in a light absorbing workpiece by the use of laser beam means providing a coherent light beam which in a pulsed manner impinges upon the surface of the workpiece in a Fresnel zone pattern. The zoned pattern is caused in a typical example by a suitable mask interposed between the laser source and workpiece surface. The thermal effect responsive to the laser beam energy produces in the workpiece a plurality of acoustic waves having a common focal point.

Resolving Power in Diffraction Microscopy with Special Reference to X-Rays

ROGERS'S1 elementary explanation of Gabor's2 technique for microscopy treats the hologram as a generalized Fresnel zone plate. I have used this idea for deriving a resolution criterion. Two point objects separated by a distance y produce two Fresnel zone patterns at the hologram with centres separated by a distance z, where z = pay/(Pa − qa), if Pa and qa are the distances from the illuminating point source of wave-length λa to the hologram film and from the film to the object, respectively. The subscript a refers to parameters of the ‘analysis’ while r will refer to the ‘reconstruction’.