  We report the development of a fast position-sensitive laser beam detector
with a bandwidth that exceeds currently available detectors. The detector uses
a fiber-optic bundle that spatially splits the incident beam, followed by a
fast balanced photo-detector. The detector is applied to the study of Brownian
motion of particles on fast time scales with 1 Angstrom spatial resolution.
Future applications include the study of molecule motors, protein folding, as
well as cellular processes.
