Optical trap
Optical trap formed by a collimated laser beam focused to a diffraction-limited beam waist through a high-NA objective. To measure displacements and forces, the laser light can be collected by a condenser and directed onto a quadrant photo diode. The laser beam deflection resulting from lateral motions of the trapped bead can be understood as first-order interference effect

New experimental techniques are developed and further developed in our lab, with emphasis on high-resolution microscopy methods and single-molecule manipulation techniques (optical traps, atomic force microscopy), single-molecule fluorescence/spectroscopy techniques and microrheology. For example, we have explained how a first order interference effect makes it possible to detect motions of a particle trapped by an opticl trap by monitoring the distribution of light intensity in the back-focal plane of the lens collecting the trapping laser light. Many subtle issues are furthermore involved in calibrating optical traps.