Department of Physics, Engineering Physics & Astronomy

Queen's University
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Department of Physics, Engineering Physics & Astronomy
Department of Physics, Engineering Physics & Astronomy

Whispering Gallery Modes Resonators: From Light Propagation to Biosensing

Claudine Allen
Université Laval

Friday, November 2, 2012
1:30 PM @ Stirling A

Abstract:

Label-free microsphere resonators were shown to be sensitive optical biosensors thanks to the very high quality factor up to Q~109 of their whispering gallery modes (WGMs). The spectral shift of a single mode of a single microsphere is the most common detection signal, but several resonances are available to probe the analyte frequency response in polarizability. However, the full spectrum of WGMs for an elliptical resonator is complicated, warranting further measures and optimizations of light propagation in this system. On one hand, our high resolution interferometric studies of the microsphere with a dual frequency comb provide both its impulse response in the time domain with 400 fs resolution and its transmission spectrum in the frequency domain with picometer resolution. In the former case, light pulses are periodically outcoupling from a ~73 μm microsphere after each round trip of ~1.13 ps with a phase delay depending on the refractive index of the surrounding medium. On the other hand, simpler WGM spectra are obtained with smaller ~10 μm fluorescent microspheres having a lower Q~2000, which are commercially available. These microspheres are then used in a more practical flow-cytometer based biosensing system making a compromise between sensitivity, sturdiness and ease of use.