There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

Biological imaging with a method for diffusion optical tomography is demonstrated. The present method is based on weight function of discrete model for scattering tissues. The weight function is given as a product form between sensitivity function and optical mean path length. The method is applied to two-dimensional imaging for inhomogeneous media by simulation. As results of the simulation, it is verified that the present method can extract parts with stronger absorption coefficient from backgrounds.

2-D Structure Reconstruction for a DOT Method based on Linear Perturbation Approach

We investigate InGaAs-GaAs MQW structure. It has a resonant transition at near 1 /spl mu/m, which is a spectral region that is especially useful for biomedical measurements. Since the resonance is a little less than the band gap energy of GaAs substrate, we do not have to remove the substrate, which significantly simplifies the fabrication process.

https://ieeexplore.ieee.org/iel4/5948/15943/00739503.pdf

Resonant photorefractive effect at near infrared in InGaAs-GaAs multiple quantum well structure

We investigated a high-density recording method to record reflection-type holograms in a volume of a recording medium. Three-dimensional shift selectivity in a LiNbO3crystal with a thickness of 0.5 mm was presented. Experimental results showed three-dimensional shift selectivity of a reflection hologram is 0.97mumtimes0.97mumtimes8.8mum with a wavelength of 514.5 nm and Fourier transform lenses with NAs of 0.28

Experimental Evaluation of Three-dimensional Shift Selectivity in Reflection-type Hologram

In this research, we have proposed a multimodal fast fluorescent imaging by an electrical tunable lens, and quantitative phase imaging by digital holography. In conventional confocal microscopy, sectioning in z direction is realized either by moving objective lens or sample stage. In order to speed up the imaging, and utilize in the specific applications such as light stimulation system in optogenetics, the sectioning is realized by changing the focal power of an electrical tunable lens. The preliminary experiment using fluorescence beads and its relation between focal power and depth change is shown.

Multimodal two-photon microscopy with electrical tunable lens

This paper provides overall analytical insights on the common-path incoherent digital holography using dual-focusing lens with diffraction gratings. Especially when one tries to seek an off-axis solution using the suggested configuration, the low temporal and spatial coherence require specific conditions on parameters of the set-up. AA mathematical explanation on the off-axis digital holography is described.

Osamu Matoba

Papers

2-D Structure Reconstruction for a DOT Method based on Linear Perturbation Approach

Resonant photorefractive effect at near infrared in InGaAs-GaAs multiple quantum well structure

Experimental Evaluation of Three-dimensional Shift Selectivity in Reflection-type Hologram

Multimodal two-photon microscopy with electrical tunable lens

Analysis of common-path incoherent digital holography using dual-focusing lens with diffraction gratings