Nonlinear optical coherence tomography

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The optical coherence tomography (OCT) microscope can produce micron-scale three-dimensional images to depths of several mm in living tissue.  Though it has made major inroads in ophthalmology, OCT suffers from several difficiencies including low contrast.  We propose to build a new instrument which will exploit the micron-scale resolution capabilities of OCT with the photon selectivity of nonlinear time-gating to improve imaging contrast and decrease data acquisition time.  Subpicosecond optical time gating, by sum-frequency mixing in a nonlinear crystal, rejects light (and its associated noise) from outside the gated time window before detection occurs.  This will yield significant improvements in imaging quality close to highly scattering media and at longer penetration depths.  Aliasing which causes ghost images and noise in current Fourier-domain implementations of OCT will also be avoided.  The time gating process is also beneficial since sample probing can be done with wavelengths around 1300nm which are optimal for sample penetration, while photodetection is done with visible light allowing the use of high performance silicon-based detector technology.  Time gating decreases the number of detector elements required thus dramatically reducing aquisition and processing time compared to standard Fourier-domain OCT systems.     This research program makes extensive use of our preexisting ultrafast infrastructure, our experience with optical pulse characterization, and our collaborations with other OCT researchers, industrial engineers and potential end users.  It is only the first step within an overall vision to integrate ultrafast optical material processing techniques with improved imaging modalities for clinical applications.  Two current graduate students require the equipment immediately for their research program.  An estimated seven additional Queen's students  (undergraduate and graduate) and at least two visiting researchers will have hands-on training on this equipment over the next three years.