We report the development of a fast position-sensitive laser beam detector. The detector uses a
fiber-optic bundle that spatially splits the incident beam, followed by a fast balanced photodetector.
The detector is applied to the study of Brownian motion of particles on fast time scales with 1 ?
spatial resolution. Future applications include the study of molecule motors, protein folding, as well
as cellular processes. © 2008 American Institute of Physics. DOI: 10.1063/1.3002422