Yukihiro Ishii

Digital phase-measuring interferometry with a tunable laser diode

A digital phase-measuring interferometer with a laser-diode source has been developed that is based on a fringe-scanning technique with a stepwise wavelength change by variation of the laser injection current. The phase is changed to produce a relative phase difference between the beams in the two arms of the interferometer. Calibrated phase shifts used for a phase-extraction algorithm are derived from one-dimensional least-squares fits to cosine fringe functions to achieve accurate results. Experimental results are presented.

Reshaping collimated laser beams with Gaussian profile to uniform profiles

A set of holographic filters was developed to convert the Gaussian intensity distribution of a collimated laser beam into a uniform one. The design and the fabricating method of the holographic filters are presented and experimental results are shown.

Heterodyne interferometry with a frequency-modulated laser diode

A digital phase measuring interferometer with a frequency-modulated laser diode using the integratedbucket technique is described. The injection current is continuously changed to introduce a time- varying phase difference between the two beams of an unbalanced Twyman-Green interferometer. The intensity of the interference patterns is integrated with a CCD array sensor for intervals of one-quarter period of the fringe. Using the intensity data a microcomputer calculates the phase to be detected. Some experimental results with the interferometer are presented; the rms repeatability obtained was lambda/80.

Flat-field linearized scans with reflection dichromated gelatin holographic gratings.

A polygonal holographic scanner that combines a reflection volume hologram on dichromated gelatin with a computer-generated hologram (CGH) is described. Such a scanning system allows for a compact folded version and highly efficient Bragg diffraction into a single order. A design of the scanner with a nonspherical wave front based on ray tracing and the damped least-squares optimization technique allows a flat-field linearized scan to be used. A suitable trade-off between field flatness and position linearity of scan is adopted. The optimized wave front designated by polynomials is encoded into a CGH. Experiments demonstrating the feasibility of this scannner are presented. Additional data on the diffraction efficiency and the spectrally diffracted intensity of the reflection volume gratings are also shown.

Color-coded character-recognition experiment with wavelength-triplexed, reflection-type holographic filters

Color-coded, simultaneous recognition of several characters is experimentally performed using wavelength-triplexed, reflection-type holographic filters made with the primary wavelengths, 632.8, 514.5, and 488.0 nm. Helpful data on the diffraction efficiency and the spectrally diffracted intensity of reflection-type holograms are presented.

Reflection holographic lens having nonspherical wavefront designed by a microcomputer

Abstract A design of a reflection holographic lens with nonspherical wavefront is described, which is based on a ray-tracing program and a simple search algorithm suitable for a microcomputer. The optimized wavefront is encoded into a computer- generated hologram (CGH). The reflection holographic lens with the optimum wavefront produced by CGH reduces the rms spot radius at large field angles, and allows for a compact folded system and for Bragg diffraction into a single order. Experimental results are shown. Helpful data on the diffraction efficiency and the spectrally diffracted intensity of reflection holograms are presented.

Reflection volume holographic scanners with field-curvature corrections

A new type of polygonal holographic scanner that combines a reflection volume hologram with a computer-generated hologram (CGH) is described. The scanner is free from the aberration of field curvature. Such a scanning system can allow for a compact folded version of the scanner and Bragg diffraction into only a single order. The equations expressing the spatial-variable image distance are derived and are fit to the phase function designated by polynomials incorporated into a CGH in terms of the least-squares method. A reflection scanner with field-curvature correction is made by interfering a diffracted wave front from this CGH with a spherical wave front having scanning focal power through a second plane hologram. Experiments demonstrating the feasibility of this scanner are presented. Raster-scan patterns using a multifaceted scanner are shown. Helpful data on the diffraction efficiency and the spectrally diffracted intensity of reflection holograms are also presented.

Optimum Holographic Disk Scanners With Bow-Locus Corrections

A design of disk-type holographic diode laser beam scanner exhibiting the bow-free and aberration-reduced properties is described, which is based on ray tracing and least-squares optimization technique. Scanning with a small bow deviation of less than ±130 μm on a 30-cm scan length has experimentally demonstrated for a holographic disk scanner recorded with the aid of a computer-generated hologram.

Holographic Display of Diffraction Patterns Suffering from Third- and Fifth-order Aberrations

The diffraction patterns suffering from third- and fifth-order aberrations are displayed by reconstructing first from the hologram of a point object under proper experimental conditions and secondly from a computer-generated hologram having the desired wavefront aberration. Experiments demonstrating the diffraction patterns with various kinds of aberration of third and fifth orders are presented. The effects of defocusing and stopping down on the aberrated diffraction patterns are observed.

Two-step Lippmann hologram: Analysis of reconstructed image blur

Abstract A dichromated gelatin Lippmann hologram is described by which the hologram is made with a Fresnel hologram used as master hologram by a two-step process. A reconstructed image without blur is shown when illuminated with white light. An angular change of diffracted wave is presented when the emulsion undergoes an increase of thickness. Both effects of changes of illuminating wavelength and readout angle on diffracted directions are considered. Calculations are helpful to investigate the image blur.