November 18
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12:00 PM
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1:00 PM
Incoherence in coherent microscopy and spectroscopy
Garth J. Simpson, PhD
Professor of Chemistry
Research Director; Young Advanced Manufacturing of
Pharmaceuticals Institute
Purdue Director; NSF Center for Bioanalytic Metrology
Purdue University
Abstract:
Nonlinear optical light/matter interactions uniquely dependent on symmetry and composition, providing image contrast inaccessible from conventional optical interactions. Such information is particularly insightful in biological microscopy, with collagen exhibiting prominent second harmonic generation (SHG) that is highly dependent on molecular ordering within the triple helical fibrils. Intriguingly, we show that SHG produced from collagen in tissue sections routinely results in significant depolarization in the detected nonlinear response. A mathematical framework based on Mueller tensors is proposed for interpreting such measurements, and mechanisms driving the introduction of incoherence are weighed within that context. While potentially viewed as an annoying interference, the incoherent component of the signal is shown to have the potential to access additional observables that are inaccessible by coherent nonlinear optics. Proof-of-concept measurements support our theoretical predictions of new chiral-specific spectroscopies enabled through incoherent optical interactions. Such measurements open up opportunities both to design new spectroscopic observables and to reinterpret prior ones.
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