Justin L. Kreuzer

A Synthetic Aperture Coherent Imaging Technique

This paper describes an active synthetic aperture coherent imaging technique which completely fills and doubles the diameter of a sparsely sampled aperture array, thus providing better imaging than would ordinarily be expected from the sparsely sampled aperture alone. The technique applies to any coherent radiation, but is most applicable to microwave (radar) and acoustic (sonar and seismic) imaging.

ACOUSTIC HOLOGRAPHIC TECHNIQUES FOR NONDESTRUCTIVE TESTING

The first part of this paper reports progress to date on an experimental investigation of the feasibility of applying holographic techniques to acoustical imaging to obtain three-dimensional images of opaque objects as encountered in nondestructive testing. Equipment was fabricated to make acoustical holograms of objects in water. Acoustical holograms were recorded by mechanically scanning an acoustical point transducer over the water’s surface in a TV-like raster. The acoustic frequency was 5 MHz. The resulting holograms were then used to make visible images. Holograms of objects examined in water, where the ultrasonic wavelength was 0.3 mm, show image detail smaller than 1 mm. A variety of acoustical holograms and their corresponding images (including one of a hole in an aluminum block) are presented and discussed. The second part of this paper presents a simplified theoretical analysis of these acoustical holograms. The effects of nonlinearities, sampling rates and pulse duration, coherent sound, and wavelength scaling on the acoustical image are discussed. The problem of three-dimensional visualization of the acoustical image is considered in detail. The third part of this paper discusses some potential uses of acoustical holographic techniques in nondestructive testing.

Acoustic Bragg Imaging with an Optical Point Source

Most acoustic imaging by optical Bragg diffraction uses a coherent line source of light to illuminate the acoustic field and cylindrical lenses to form one conventional optical point image for each point in the acoustic field. Likewise it is generally realized that an optical point source of illumination produces an optical ring image for each acoustic field point [Ref. 1]. In general, the diameter of the ring is larger than the theoretical acoustic resolution, thus providing a poor image of the acoustic field. I will discuss three possible techniques for producing optical point images of acoustic field points with a point source of illumination. (1) The desired optical point images are formed directly when the acoustic wavelength equals one half the optical wavelength. (2) If the optical point source coincides with the acoustic point, the ring image reduces to a point image. (3) The optical ring image can be changed into a point image by a second imaging operation through a second acoustic field or a spatial filter.

Precision Alignment For X-Ray Lithography

X-ray lithography promises cost-effective integrated circuit production with submicron resolution. Achievement of this promise requires precision mask-to-wafer alignment over the whole wafer. This paper describes Perkin-Elmers X-100 full-field X-ray lithography system with emphasis on the alignment subsystem. The alignment subsystem provides six degrees of freedom alignment between wafer and mask with an air gauge gap setting technique and a laser based physical optics lateral alignment system. These techniques were selected to be compatible with the subfield-stepper systems needed to pattern wafers over 100 mm in diameter. The physical optics technique has demonstrated alignment stability with signal-to-noise ratios representing less than 0.01 micron rms error for a 30 Hz bandwidth. The alignment system and its relation to the entire lithographic system is described in detail. X-ray exposed alignment overlays are shown.