High Q-factors and small mode volumes have made toroidal optical microresonators exquisite sensors to small shifts in the effective refractive index of the WGM modes. Eliminating contaminants and improving quality factors is key for many different sensing techniques, and is particularly important for photothermal imaging as contaminants add photothermal background obscuring objects of interest. Several different cleaning procedures including wet- and dry-chemical procedures are tested for their effect on Q-factors and photothermal background. RCA cleaning was shown to be successful in contrast to previously described acid cleaning procedures, most likely due to the different surface reactivity of the acid reagents used. UV-ozone cleaning was shown to be vastly superior to O2 plasma cleaning procedures, significantly reducing the photothermal background of the resonator.
Erik H. Horak, Kassandra A. Knapper, Kevin D. Heylman, and Randall H. Goldsmith, "Cleaning procedure for improved photothermal background of toroidal optical microresonators," Proc. SPIE 9923, Physical Chemistry of Interfaces and Nanomaterials XV, 99230Z (Presented at SPIE Nanoscience + Engineering: August 30, 2016; Published: 26 September 2016); https://doi.org/10.1117/12.2238001.
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