Angular Domain Optical Imaging of Structures Within Highly Scattering Material Using Silicon Micromachined Collimating Arrays

摘要

Optically Tomography within highly scattering material has focused on Coherence Domain and Time Domain methods: both detecting the shortest path photons over the dominant randomly scattered background light. Angular Domain Imaging instead uses collimators, small acceptance angle filters, to observe only those photons closely aligned to a laser light source. A linear collimating array was fabricated using silicon surface micromachining consisting of 51 μm wide by 10 mm long etched channels with 102 μm spacing very high aspect ratio (200:1) 20 mm wide array. With careful array alignment to a laser source, restricted to a linear beam, the unscattered laser light passes directly through the channels to a CCD detector, and the channel walls absorb the scattered light at angles >0.29 degrees. With a computer controlled Z axis objects within a 1 cm thick scattering material were scanned quickly. High contrast 150 μm lines/spaces at the medium front were observed at scattered to ballistic photon ratios >5x10~5:1 with a 10 mm beam. Narrowing the beam to 130 μm width produces detectable images >3x10~8:1. Objects closer to the detector were more visible, and mid point objects were detectable >10~9:1. Smaller channels and longer arrays should enhance detection by factors of > 100.