Dependence of silicon position-detector bandwidth on wavelength, power, and bias

We have developed a two-LED wobbler system to generate the spatial displacement of total light intensity on a detector surface, facilitating the acquisition of frequency responses up to 600 kHz with high accuracy. We have used this setup to characterize the low-pass filtering behavior of silicon-based position detectors for wavelengths above 850 nm by acquiring the frequency responses of several quadrant detectors and positionsensitive detectors as functions of wavelength, applied bias voltage, and total light power. We observed an increase in bandwidth for an increase in applied bias voltage and incident-light intensity. The combined effect of these parameters is strongly dependent on the detector used and has significant implications for the use of these detectors in scanning probe and optical tweezers applications

Scanning Probe Optical Tweezers: a new tool to study DNA-protein interactions

The main goal of the work described in this thesis is to construct a microscope in which OT and scanning probe microscopy (SPM) are combined, to be able to localize proteins while simultaneously controlling the tension within the DNA molecule. This apparatus enables the study of the effect of tension in the molecule on the functional properties of DNA-binding proteins. An advantage of the `Scanning Probe Optical Tweezers¿, i.e. SPOT-microscope, is that the DNA-protein interactions are not obstructed by the presence of a supporting surface as is the case for imaging using conventional SPM techniques