Chirped-Pulse Interferometry - Enhanced Optical Imaging using Chirped Laser Pulses

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Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition speed because living systems tend to move around. At the same time it must use low power to avoid harming the specimen. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. Interference is the pattern of light and dark regions created when two beams of light are superposed. The resolution of OCT is determined by the length over which the light used will interfere. Unfortunately, dispersion, the frequency dependent velocity of light, hurts the imaging resolution by broadening interference features and lowering interference contrast. A technique called quantum-OCT (QOCT) is immune to dispersion but requires quantum mechanically entangled photon pairs. Entanglement is a property of quantum mechanical systems involving two or more particles that cannot be described separately. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A pulse is a short burst of laser light, lasting as little as a few millionths of a billionth of a second. A chirped pulse is one where the frequency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT. CPI has been demonstrated in the lab, but with insufficient resolution and power levels too high to use with living samples. In the proposed project we will build a prototype setup using CPI for dispersion-cancelled 3D imaging of a biological sample, with a resolution comparable to conventional OCT systems. This will be a major advance in biomedical imaging.