Takeo Sawatari

Optical heterodyne scanning microscope.

A new optical heterodyne scanning microscope is described in which both the illumination beam and reference beam scan the object in synchronization. Characteristics of the microscope are similar to those of the laser scanning microscope. The present system, however, has additional advantages in that the object illumination can be at least one order of magnitude less intense and that ambient light has no effect for images. Preliminary experimental results will be shown, including a two-dimensional cross-section pattern from a 3-D object, unfocused image rejection characteristics, and images of some biological samples.

Fresnel-Zone-Plate Spectrometer with Central Stop*

The marked chromatic aberration of a Fresnel-zone-plate lens can be used as a variable narrow-band optical filter, and thus a holographic spectrometer. The filtering properties of the zone plate are analyzed, with particular emphasis on the effect of a central stop over the low-order rings. It is shown that the central stop can markedly improve the rejection of frequencies outside the pass band without significant degradation of the spectrometer resolution.

Real-time noncontacting distance measurement using optical triangulation

Real-time noncontacting distance measurement systems are constructed using photogrammetric principles. The system is used to measure a distance between two points specified by sharp visible contrast change under optical illumination. Tests of the system indicate that it can measure the distance with a repeatability of better than one part in 10(4).

Holographic Aperture Synthesis via a Transmitter Array

The problem of the synthesis of a large holographic aperture by means of a smaller aperture and an array of sources is addressed. Emphasis is placed on the problem of parallel acquisition of the contributions associated with the different sources and on a comparison between alternative superposition approaches (either superposition of holograms prior to reconstruction or superposition of reconstructed image fields). Experimental results are presented in which synthetic-aperture images due to a 10 × 10 hologram array and a 2 × 2 transmitter array are compared with images due to (a) a 10 × 10 array and a single transmitter, and (b) a 20 × 20 array and a single transmitter.

Optical Profile Transducer

A noncontacting optical transducer, which measures the profile of machined surfaces, was constructed and tested. The profile transducer consists of a microscope objective, a point-source illuminator and two photo-detectors. The dynamic range of the instrument is typically 500 microinches with an accuracy of better than 10 microinches. The output of this transducer is a profile signal along a line on the surface under examination. The profile of a machined surface obtained by the optical-transducer correlates very well with that obtained by a mechanical Proficorder® which uses a diamond stylus. Principles of operation, results of various performance tests and potential applications of the optical-transducer are discussed.

The use of multidimensional perceptual models in the selection of sonar echo features

The development of an accurate and efficient sonar-target classification system depends upon the identification of a set of signal features which may be used to discriminate important classes of signals. Feature selection can be facilitated through the identification of perceptual features used by human listeners in discriminating relevant sonar echoes. This study was conducted to establish a more reliable means of identifying perceptual features in terms of physical signal parameters as an initial step toward the development of an automatic sonar-target classification system. The results of an experiment involving eight subjects and six sonar echoes are presented. A model of the perceptual structure of these echoes was derived from subject similarity judgments using a multidimensional scaling (MDS) technique. It was found that three perceptual features accounted for the similarity judgments made by the human listeners. Echoes modified along candidate physical dimensions were employed to aid in the identification of perceptual dimensions in terms of physical signal parameters. The three perceptual features could be associated with signal parameters involving the amplitude envelope of the echoes.

Two-Dimensional Null Processing

A beamforming technique based on the simultaneous operation of the null processing method in both the spatial and temporal domains successfully enhances a weak target signal by rejecting a number of strong localized interferences. This two-dimensional null processing (2-DNP) technique is compared to the previously developed adaptive null processing (ANP) method and conventional beamforming methods, in part using computer simulation results. The application of the 2-DNP method to tracking a moving target is also discussed.

Experimental analysis of surface flaw detection using grazing angle illumination.

The capability of a method using grazing angle illumination for automated surface flaw detection has been analyzed experimentally for actual flaws. Bearing rollers were chosen as test samples and two different methods, low angle scattered light observation and high angle scattered light observation, were evaluated. For the latter method, an analysis of the data from a number of samples results in a sample classification that accurately matches that determined by careful visual inspection.