Publications by authors named "Robert Kowarsch"

2 Publications

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Compressional-Wave Effects in the Operation of a Quartz Crystal Microbalance in Liquids:Dependence on Overtone Order.

Sensors (Basel) 2020 Apr 29;20(9). Epub 2020 Apr 29.

Institute of Physical Chemistry, Clausthal University of Technology, Arnold-Sommerfeld-Str. 4, D-38678 Clausthal-Zellerfeld, Germany, (F.M.).

The operation of the quartz crystal microbalance (QCM) in liquids is plagued by small flexural admixtures to the thickness-shear deformation. The resonator surface moves not only in the transverse direction, but also along the surface normal, thereby emitting compressional waves into the liquid. Using a simple analytical model and laser Doppler vibrometry, we show that the flexural admixtures are stronger on the fundamental mode than on the overtones. The normal amplitude of motion amounts to about 1% of the transverse motion on the fundamental mode. This ratio drops by a factor of two on the overtones. A similar dependence on overtone order is observed in experiments, where the resonator is immersed in a liquid and faces an opposite planar wall, the distance of which varies. Standing compressional waves occur at certain distances. The amplitudes of these are smaller on the overtones than on the fundamental mode. The findings can be rationalized with the tensor form of the small-load approximation.
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http://dx.doi.org/10.3390/s20092535DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7249204PMC
April 2020

Superresolution reflection microscopy via absorbance modulation: a theoretical study.

Opt Express 2018 Mar;26(5):5327-5341

Absorbance modulation enables lateral superresolution in optical lithography and transmission microscopy by generating a dynamic aperture within a photochromic absorbance-modulation layer (AML) coated on a substrate or a specimen. The applicability of this concept to reflection microscopy has not been addressed so far, although reflection imaging exhibits the important ability to image a wide range of samples, transparent or opaque, dielectric or metallic. In this paper, a simulation model for absorbance-modulation imaging (AMI) in confocal reflection microscopy is presented and it is shown that imaging well beyond the diffraction limit is feasible. In addition, we derive analytical design equations and estimate the dependence of the achievable resolution and pixel dwell time on relevant parameters, such as the AML properties and the applied light powers. We prove the validity of these equations through a comparison with the simulation results and we show that a resolution enhancement down to 1/5 of the diffraction limit is possible.
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http://dx.doi.org/10.1364/OE.26.005327DOI Listing
March 2018