Dispersion-free coherence tomography using chirped lasers

Optical coherence tomography (OCT) is a new non-invasive imaging technology based on "white-light" or low- coherence interferometry that is proving to have great benefit for biological sciences and medicine, particularly in disease detection, since it allows high-resolution depth profiles of the samples under consideration [3]. However, material dispersion is a major problem in OCT since it reduces both contrast and resolution with increasing sample depths, and thereby drastically limits the potential range of OCT applications. Exciting developments in quantum interferometry have previously led to the proposal and demonstration of quantum-optical coherence tomography (Q-OCT) [4, 5]. This technique relies on Hong-Ou-Mandel (HOM) interferometry [6] which utilizes frequency-entangled photon pairs. The most important advantage of this technique is that it automatically cancels the most pronounced type of dispersion [7]. In addition, it is insensitive to phase fluctuations and unbalanced photon loss in the interferometer, and has a better resolution than OCT. Unfortunately, entangled photon pairs are difficult to create, manipulate and detect and this has restricted Q-OCT to basic proof-of-principle demonstrations in specialized laboratories. Using insights gained from quantum information science, Prof. Resch`s group at the host institution has recently introduced and demonstrated a completely classical technique based on the time-reversal symmetry of quantum mechanics that achieves all of the standard advantages of HOM interferometry by using oppositely-chirped laser pulses [12]. Moreover, since it relies on classical lasers instead of entangled photons, it achieves these features with millions of times more signal, making it an attractive candidate for dispersion-free OCT. The main aim of the proposed project is to design and build an optical coherence tomography (OCT) prototype based on this recently invented chirped-pulse interferometry (CPI) technique. The research will take this initial demonstration of CPI to the next stage by developing an imaging prototype capable of measuring high-resolution OCT images with automatic dispersion cancellation at macroscopic power levels. By improving the CPI resolution for axial imaging and by designing an automated X-Y scanning apparatus we aim to construct a complete tomographic image of samples with varying complexity. The target of this research project is to image a biological sample, such as an onion skin, a standard test sample in OCT, and ultimately human or animal tissue. This would represent a significant advance in biomedical imaging technology and a step towards more powerful and reliable OCT. This is an interdisciplinary project that allows me to bring in my skill and expertise in the theory and experiment of quantum information as well as classical optics to benefit research in biological and biomedical fields. A promising side line of the proposed research is to investigate and potentially find other situations in which the time-reversal approach of CPI can outperform classical or quantum interferometers [16]. Research in this direction would yield insights that may help drive the design and development of superior and more practical classical technologies. This line of research addresses one of the central debates in quantum information - which tasks truly benefit from quantum effects -while converting quantum intuition into practical technology.