| Description |
"Photon-Counting Optical Coherence-Domain Imaging"
ABSTRACT:
Coherence-domain imaging (CDI) systems can be operated in a single-photon counting mode, offering low detector noise; this in turn leads to increased sensitivity for weak light sources and weakly reflecting samples. In this thesis, I demonstrate that excellent axial resolution can be obtained in a photon-counting coherence-domain imaging (PC-CDI) system that uses light generated via spontaneous parametric down-conversion (SPDC) in a chirped periodically poled stoichiometric lithium tantalate (chirped-PPSLT) structure, in conjunction with a niobium nitride superconducting single-photon detector (SSPD). The bandwidth of the light generated via SPDC, as well as the bandwidth over which the SSPD is sensitive, can extend over a wavelength region that stretches from 700 to 1500 nm. This ultra-broad wavelength band offers a near-ideal combination of deep penetration and ultra-high axial resolution for the imaging of biological tissue. The generation of SPDC light of adjustable bandwidth in the vicinity of 1064 nm, via the use of chirped-PPSLT
structures, is novel. To demonstrate the usefulness of PC-CDI, I have constructed images for a hierarchy of samples of increasing complexity: a mirror, a nitrocellulose membrane, and a biological sample comprising onion-skin cells. The potential usefulness of this technique in a standard configuration is limited, however, by the presence of 1/f-type noise in the source of illumination. I have therefore investigated this noise for various sources of light that are useful in optical imaging. Finally, I consider another CDI configuration, spectral-domain imaging, and show that the notion of compressed sensing can be useful for simplifying the experimental configuration. |
