AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Utilizing a Sub-Micron Silicon Nitride Waveguide as Single Particle Aerosol Detector
ANTON BUCHBERGER, Paul Maierhofer, Martin Sagmeister, Victor Sidorov, Jochen Kraft, Alexander Bergmann, Graz University of Technology
Abstract Number: 420 Working Group: Aerosol Physics
Abstract We present first results of a novel particle detector utilizing the interaction of particles with the evanescent field at the surface of a sub-micron waveguide. The transmission mechanism of light in a guiding structure is based on total internal reflection at the interface of a high to a low refractive index medium. The electromagnetic field of light guided through the high index medium does not abruptly vanish at this interface, but decays exponentially with a certain penetration depth. Hence, a portion of the total electromagnetic field is transmitted in this so-called evanescent region where it can interact with analytes such as particles. Interaction occurs in the form of scattering and absorption, thereby changing the total transmitted power through the waveguide. This influence to the total transmission is weak for guiding structures in the size range of standard single mode fibers (8-10 µm). By tuning the dimensions of waveguide structures to the range of the wavelength of the transmitted light, the ratio of the evanescent field to the total field can be drastically increased, which enhances the sensor effect strongly. The total transmission of light through such a structure is highly sensitive to any kind of perturbation in the evanescent region, like e.g. aerosol particles.
For the proof of principle, we use a silicon nitride waveguide with sub-micron dimensions for detecting surface impacted PSL spheres utilizing their influence to the total transmission through the device. The guiding structure consists of a silicon nitride strip as high index medium surrounded by air and silicon dioxide as low index medium. First deposition experiments with PSL spheres in the size range between 0.2 and 1 µm feature a relative decrease of the total transmission in the order of a few percent per deposited particle, revealing the potential of waveguides as highly sensitive particle detectors.