Plane Reference Wave Research Articles

Multilayer volume holographic optical memory

We demonstrate a scheme for volume holographic storage based on the features of shift selectivity of a speckle reference-wave hologram. The proposed recording method permits more-efficient use of the recording medium and yields greater storage density than spherical or plane-wave reference beams. Experimental results of multiple hologram storage and replay in a photorefractive crystal of iron-doped lithium niobate are presented. The mechanisms of lateral and longitudinal shift selectivity are described theoretically and shown to agree with experimental measurements.

Electron holography of p-n junctions

A wide holographic field of view (up to 15 μm in the Hitachi-HF2000) is achieved in a TEM by switching off the objective lens and imaging the sample by the first intermediate lens. Fig.1 shows the corresponding ray diagram for low magnification image plane off-axis holography. A coherent electron beam modulated by the sample in its amplitude and its phase is superimposed on a plane reference wave by a negatively biased Möllenstedt-type biprism.Our holograms are acquired utilizing a Hitachi HF-2000 field emission electron microscope at 200 kV. Essential for holography are a field emission gun and an electron biprism. At low magnification, the excitation of each lens must be appropriately adjusted by the free lens control mode of the microscope. The holograms are acquired by a 1024 by 1024 slow-scan CCD-camera and processed by the “Holoworks” software. The hologram fringes indicate positively and negatively charged areas in a sample by the direction of the fringe bending (Fig.2).

Spatial-frequency version theory of three-dimensional holograms

A spatial-frequency version of high efficiency three-dimensional holograms of complex wave fields has been achieved. It has been shown that a three-dimensional hologram recorded by a plane reference wave may be described by means of a complex transfer function, which is found here analytically. Analysis of amplitudephase wave field distortions, under different recording and reconstruction conditions, has been carried out.

Resolution studies for electronic holography

The output of an electronic holographic apparatus represents the magnitude and phase of the coherent light reflected from a three-dimensional object. The amplitude and phase can be fed into a spatial light modulator for three-dimensional object reconstruction, and the technique is thus named electronic holography. Resolution studies of recording and display devices for electronic holography are presented. The theoretical analysis for electronic holography is first carried out. Mathematically, the additive noise at the exposure of an electronic hologram is more serious than that at the reconstruction. Simulation is used to verify the theoretical results, and the resolution requirements for an electronic hologram are deduced. In our simulation, the point source is placed 500 mm in front of the recording device and the reference plane wave is tilted at angle π/4 in the - y direction with the normal to the recording plane. To discrimmate a two-point object with 0.17-mm separation, an 8-bit 256x256 charge injection device with a pixel size of 10 x 10 μm 2 is necessary. In addition, the additive noise from the ambient light during the exposure or reconstruction of an electronic hologram should be less than 1/100 of the signal amplitude for a 40-dB output SNR.

Video-rate electron-holographic interference microscopy and its application to dynamic observation of electromagnetic fields

The system described here provides video-rate observation by using a liquid-crystal spatial light modulator as a rewritable electron-hologram medium. Time-sequential interference micrographs are produced by superimposing a plane reference wave on the object wave reconstructed from the hologram displayed on the modulator. Experimental observations of the magnetic field of a barium ferrite particle and of dynamic domain-wall motion in a thin ferromagnetic film are shown. The sources of error in system are discussed, and a distortion-free system is proposed.

Real-time electron-holographic interference microscopy with a liquid-crystal spatial light modulator

An electron-holographic interference microscope that produces a time-sequential interference micrograph at a TV rate is developed. In this system, the electron off-axis hologram detected with a TV camera is transferred to a liquid-crystal spatial light modulator as a video signal. The liquid-crystal spatial light modulator can function as a thin amplitude hologram or a thin phase hologram. Time-sequential interference micrograph is obtained at a TV rate by superimposition of a plane reference wave onto the reconstructed object wave. Experimental results for observing a dynamic domain-wall motion in thin Permalloy film are demonstrated.

Optical perfect-shuffle interconnection using a computer-generated hologram

We propose the use of a computer-generated hologram that combines a fanout and focusing element that can be used to perform an optical perfect-shuffle interconnection. The hologram is designed by calculation of the interference fringes between diverging waves from four point sources and a reference plane wave. With this element we show experimentally the resulting perfect-shuffle pattern. The use of the computer-generated hologram makes it easy to implement a planar optical perfect-shuffle interconnect, which is compact, has low aberration, and is easy to align. The planar optics configuration for a perfect-shuffle interconnection network is also discussed.

Analysis of hybrid holographic gratings by thin-grating decomposition method

The thin-grating decomposition method is employed to evaluate the properties of hybrid holographic gratings, i.e., volume holograms recorded with a plane reference wave and an object wave produced by a periodic computer-generated hologram. The effects of the object wave period, defocusing, spatial filtering, reference to object beam ratio, and off-Bragg incidence on the quality of the regenerated signal are investigated; hybrid kinoform array generators are used as an illustration.

Storage of 500 high-resolution holograms in a LiNbO_3 crystal

We have recorded (at room temperature) as many as 500 high-resolution, uniformly diffracting volume holograms in a single Fe-doped LiNbO(3) crystal. The holograms were stored by angularly multiplexing a plane-wave reference beam. The graphical procedure that we used to compute exposure schedules is described. Experimental results are also presented.

Off-axis phase-only filter for pattern recognition

A new kind of amplitude-encoded phase-only filter (AE POF) is presented. The interference of the Fourier phase value with a tilted plane reference wave encodes the pure Fourier phase information of the object wave and results in an off-axis phase-only filter (OA POF). After the binarization step the filter function is recorded directly into the recording medium in final size using a laser scanner. Comparing them with the conventional matched filter, the conventional phase-only filter, and the AE POF, as well as their binary versions, we discuss the performances of OA POFs (OA BPOFs), present computer simulations, and demonstrate experimental results.

Quantitative i n s i t u characterization of x-ray mask distortions

The control of x-ray mask distortion is a central issue in x-ray lithography technology. Three causes of distortion have been examined: the interaction between a stressed absorber and substrate, the heating of the mask during x-ray exposure, and the radiation damage resulting from the cumulative absorption of the x rays. Interferometric techniques have been used to measure both in-plane distortion (IPD) and out-of-plane distortion (OPD). To measure OPD, wave fronts reflected from the mask surface are compared with a reference plane wave. For IPD it is necessary to have a diffraction grating on the mask. IPD causes changes in the grating pitch that result in the changes in the interference pattern. For thermal studies, an in situ shear interferometer was used to measure both OPD and IPD. Temperature increases were monitored using an infrared camera. The results have been modeled using the finite element program ansys. The distortion due to aborber substrate interaction was observed to occur at pattern edges. Thermal distortions were observed to cause IPD in regions with no absorber and both IPD and OPD for areas covered with absorber. Radiation damage was found to cause both IPD and OPD. The OPD was in the form of a plateau and can be modeled assuming the relaxation of the material is dependent on the absorbed dose and taking into account the depth dependence on absorption in the mask.

Photorefractive holographic recording in strontium barium niobate fibers

We describe what are to our knowledge the first photorefractive holographic recordings in a fiber. A plane-wave reference and an image-carrying object beam are incident upon the fiber in a reflection geometry. We report results on the angular sensitivity of the recordings, the image quality, and readout efficiency as a function of the reference-wave input angle when the object wave propagates along the bore of the fiber. These experiments are carried out for two relatively short, 4- and 8-mm, multimode 1-mm-diameter fibers. The results suggest that an array of fibers might favorably replace bulk materials for certain computer and signal-processing applications.

Phase-Only Composite Filter

Combining the concepts of phase-only filtering and multiple-exposure holography, we propose a method for making a phase-only composite filter using a plane reference wave as the carrier. We used this filter for the optical recognition of four kinds of hardware items, and the results of a computer simulation are presented. The characteristics and possible applications of this correlation recognition method are discussed.

Holographic associative memory with nonlinearities in the correlation domain

We describe a shift-invariant all-optical holographic associative memory implemented using phase conjugate mirrors and Fourier transform holograms. A key feature of our system is the large storage capacity obtained through the use of nonlinearities in the correlation domain. The use of angularly multiplexed plane wave reference beams allows access to the correlation domain where nonlinearities in the phase conjugate mirrors can be used to reduce greatly crosstalk and correlation noise.

Multiple holographic transmission gratings in silver halide emulsion

Holograms, recorded in silver halide emulsion by a plane reference wave andN cylindrical object waves, are measured as a function of the replay beam angle both for sequential and simultaneous recording. A theoretical model, based on coupled-wave differential equations, is presented. Numerical results for theN=3 case are compared with experiments and good agreement is found. Cross-modulation effects caused by simultaneous recording are discussed and are shown to be detrimental to the fidelity of reproduction of the original object beams. The results are relevant to more general hologram configurations, e.g., display holograms.

PARTIALLY COHERENT RADIATION AT X-RAY WAVELENGTHS

PARTIALLY COHERENT RADIATION AT X-RAY WAVELENGTHS

Image transmission through a turbulent medium using a point reflector and four-wave mixing in BSO crystal

A method of one-way image transmission through a turbulent medium is presented using four-wave mixing in BSO crystal. In this method, a pointlike reflector is placed on the observation plane to return part of the incident wave, giving the instantaneous wave propagation function of the turbulent medium to the image transmission side. The returned wave together with the plane reference wave and the Fourier-transformed input image wave is impinged in BSO crystal to modulate the image wave by the phase-conjugate wave, so that transmission of the image with reduced turbulence effects is achieved. The principle and laboratory experimental results are given.

Use of a holographic filter to modify the coherence of a light field

A new technique for modifying the coherence of a light field is described theoretically, and experimental confirmation is presented. A hologram of a coherently illuminated spatially random diffuser and a reference plane wave is recorded. When the processed hologram is placed back into position and the diffuser is illuminated by partially coherent light, the coherent reference plane wave is reconstructed by the hologram. Thus this optical system can be used to separate a coherent component from partially coherent illumination.

Structure of the interference field of plane electromagnetic waves in uniaxial crystals

The starting point for understanding the processes of holographic writing and reading of information lies in the structure of the interference pattern arising in the detection medium when its surface is exposed to two (reference and object) plane (Fourier component) waves. Refracting at the surface of the crystal, each of them excites two waves, the ordinary and extraordinary, which propagate in different directions. These four waves, interfering among themselves, form a family of periodic spatial intensity lattices, the parameters of which also determine the basic properties of the hologram [i]. In the present work we study the structure of such lattices in a uniaxial crystal as a function of the parameters of the waves, the orientation of the optic axis, and the crystal anisotropy.

Optical phase measurement in real time

A method has been developed for the real-time measurement of optical phase. The optical wave whose phase is to be measured is interfered with a spatially coherent plane-wave reference on the face of a photodetector array. The irradiance is measured simultaneously at all array elements for each of three specific phase shifts of the reference, and the phase and magnitude at each array element are calculated from the three measured irradiances by a simple algorithm. The method can be used for hybrid optical-digital analog computation of 2-D Fourier transforms: information is introduced coherently into the front focal plane of a lens with a spatial light modulator, and the phase and magnitude are measured in the back focal plane. Experimental results of the Fourier transform technique are described.