Optical Sciences

Biomolecules and nanostructures

The Optical Sciences group studies the interaction of light and matter. Our current focus is on detection and sensing/imaging with an emphasis on the development of integrated photonics. We are part of Twente University's Department of Science and Technology and member of the MESA+ institute.


Tuning fork shear-force feedback

(full pdf)

Ruiter AGT, van der Werf KO, Veerman JA, Garcia-Parajo MF, Rensen WHJ, van Hulst NF
vol 71 issue 1-4: p149-p157 MAR 1998

Investigations have been performed o­n the dynamics of a distance regulation system based o­n an oscillating probe at resonance. This was examined at a tuning fork shear-force feedback system, which is used as a distance control mechanism in near-field scanning optical microscopy. In this form of microscopy, a tapered optical fiber is attached to the tuning fork and scanned over the sample surface to be imaged. Experiments were performed measuring both amplitude and phase of the oscillation of the tuning fork as a function of driving frequency and tip-sample distance. These experiments reveal that the resonance frequency of the tuning fork changes upon approaching the sample. Both the amplitude and the phase of the tuning fork can be used as distance control parameter in the feedback system. Using the amplitude a second-order behavior is observed, while with phase o­nly a first-order behavior is observed. Numerical calculations confirm these observations. This first-order behavior results in an improved stability of the feedback system. As an example, a sample consisting of DNA strands o­n mica was imaged which showed the height of the DNA as 1.4 +/- 0.2 nm. (C) 1998 Elsevier Science B.V. All rights reserved.
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