Sorting of micrometer-sized dielectric objects by optical forces

Optical forces are frequently utilized in microbiological and medical research, colloidal chemistry and analysis of stochastic motion. Besides common use of optical tweezers for manipulation with living cells, polymer probes or oil droplets, advanced modification of optical setup can be used to run micro-rotors, measure forces in piconewton range, stretch living cells or sort particles without mechanical contact. Sorting techniques are either based on active feedback loop where particles are analyzed by image processing or spectroscopy techniques and moved accordingly by optical tweezers into collecting or waste channels, respectively, or on passive mechanism where optical forces in complex interference pattern differ with respect to particle size, optical properties or internal structure. We will present the passive sorting in moving interference fringes and three-beam static interference pattern. Among others, borosilica spheres, polymer spheres and discs and living cells are separated by changing the period of the fringes. Separation with respect to both size and shape of the particles will be presented.