Optical sorting and detection of submicrometer objects in a motional standing wave

An extended interference pattern close to the surface may result in either a transmissive or an evanescent surface field for large-area manipulation of trapped particles. The affinity of differing particle sizes to a moving standing-wave light pattern allows us to hold and deliver them in a bidirectional manner and demonstrate experimentally particle sorting in the submicrometer region. This is performed without the need of fluid flow (static sorting). Theoretical predictions support the experimental observations that certain sizes of colloidal particles thermally hop more easily between neighboring traps. A generic method is also presented for particle position detection in an extended periodic light pattern and applied to characterization of optical traps and particle behavior.