Progress Toward a Practical 100 MHz Scanning Laser Tomographic Acoustic Microscope
This paper presents the results of research into the development of a Scanning Laser Acoustic Microscope (SLAM) which produces diffraction corrected tomographs from a series of shadowgraphic micrographs. This demonstration is based on the following work. By modifying an in-house 100 Mhz SLAM, we acquired data containing both the amplitude and phase information needed for diffraction tomography algorithms. The principle modification was a new general purpose single sideband synchronous demodulation receiver based on phase coherent quadrature detection with selectable output of either the upper or lower sideband. The images produced by the system were digitized in real-time into a 256 × 240 grid of 6–bit pixels. An analysis of the principle characteristics of the system transfer function was performed to allow modification of the acquired data so that a better representation of the detected sound field could be used in reconstruction algorithms. We demonstrated extraction of the amplitude and phase information by digitally reconstructing both amplitude and phase images of a series of phantoms. The phantoms were constructed to produce understandable images of a series of amplitude and phase variations, fine spatial detail, and known diffraction from a circular aperture. Some phantoms were used to obtain two dimensional diffraction-corrected holographic reconstructions by back propagation in Fourier space. (See the companion paper “Subsurface Imaging in Acoustic Microscopy” by Z-C. Lin, H. Lee and G. Wade.) The tomographic acoustic microscope could produce unambiguous images needed in materials characterization, detailed inspection of micro-electronic components, nondestructive evaluation of solid-state materials and non-invasive imaging of biological samples.
KeywordsDetection Plane Circular Aperture Laser Spot Size Amplitude Image Acoustic Microscopy
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