Optical Imaging of Objects Within Highly Scattering Media Using Silicon Micromachined Collimating Arrays

摘要

Optical imaging of objects within highly scattering media requires the detection of ballistic/quasiballistic photons through these media. Recent works have used Phase/Coherence Domain or Time Domain Tomography (femtosecond pulses) to detect the shortest path photons through scattering media. Our collimation detection uses Small Acceptance Angle Devices to extract photons emitted within a small source angle. This work employs a high aspect, micromachined collimating detector array fabricated by high-resolution silicon surface micromachining. Consider a linear collimating array of very high aspect ratio (200:1) containing 51*1000 μm etched channels with 102 μm spacing over a 10 mm silicon width. With precise array alignment to a laser source, unscattered light passes directly through the channels to the CCD detector and the channel walls absorb the scattered light at angles >0.29°. Objects within a scattering medium were scanned quickly with a computer-controlled Z-axis table. High-resolution images of 100 μm wide lines and spaces were detected at scattered-to-ballistic ratios of 500,000:1. At >5,000,000:1 ratios, a uniform background of scattered illumination degrades the image contrast unless recovered by background subtraction. Simulations suggest smaller channels and longer arrays could enhance detection by factors greater than 100. Detection using Silicon Micromachined Collimating Arrays are also nearly wavelength independent.