Reference interferometry techniques for nanodetection and biosensing




Herchak, Steven

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Three reference interferometry techniques which overcome the effects of laser jitter noise in sensitive nanodetection experiments are presented. Experiments performed with a Mach-Zehnder interferometer in parallel with an ultrahigh-Q microresonator for nanodetection of a record polystyrene particle size down to 12.5 nm radius are described. The first interferometry technique employed in this work sees the implementation of a Mach-Zehnder interferometer in parallel with a microsphere to show the versatility of these devices across detection systems. Using a least squares fitting method on simulated results, it is shown that the parallel Mach-Zehnder can detect resonant wavelength shifts of the microcavity down to hundreds of attometers, provided sufficient system stability. Furthermore, a cavity resonant wavelength shift detection sensitivity of 0.14 femtometers is observed experimentally with a loaded microsphere Q of 2.0x10^8 in a buffer solution. For experiments which require high optical intensities, splitting off part of the optical power for use in an interferometer may reduce the dynamic range of power sensitive measurements. To rectify this problem, two in-line systems are investigated: the serial connected Mach-Zehnder and Fabry-Perot interferometers. According to simulation, the use of a Mach-Zehnder interferometer is not suitable for serial interferometry. In light of this problem, a serial Fabry-Perot interferometer is proposed. It is shown that with a least squares fitting method to fit experimental data the inline Fabry-Perot interferometer can measure resonant wavelength shifts down to a few femtometers, again provided sufficient system stability. Experimental results show a cavity resonant wavelength shift detection sensitivity of 0.5 femtometers observed with a microsphere Q of 2.1x10^7 in a buffer solution.



Nanodetection, Nanophotonics, Optics, Interferometry, Biosensing