Photonic force microscope

Photonic force microscopy (PFM) is an optical tweezer based microscopy technique. A small dielectric particle (20 nm to several micrometres) is held by a strongly focused laser beam.

The forward scattered light, i.e. the light that passes through the bead, can be collected by a lens and projected onto a Quadrant Photo-Diode (QPD) or a Position Sensing Detector (PSD), which permits it to detect the position of the bead in 3D with very high accuracy (down to 10 nm) and at a very high rate (up to 1 MHz). From the measured positions it is possible to derive the optical potential in which the particle is held.

If then a force is applied on the particle, this can be estimated from the displacement of the particle itself.

The Photonic force microscope was developed and invented by Hoeber and Stelzer while teaching a biophysics undergraduate course at the University of Bristol.