Optical tracking of spherical micro-objects in spatially periodic interference fields

We present a new method that provides precise detection of micro-object position with respect to a spatially periodic illumination field. Altering the mutual position of the object and the illumination field causes that a pattern of scattered light detected perpendicularly by a CCD camera changes. We present a procedure how to employ this pattern changes to track micrometer-size object in the standing wave and how to apply this method to optical tracking of Brownian particle even in periodic illumination field in motion.