Laser beam interference and its applications in optical micromanipulation

Optical interference of two or more waves with different wave vectors generates a periodic, harmonic spatial profile of the optical intensity. This well known property combined with mechanical effect of light offers an excellent route to organize and manipulate large ensembles of microobjects in a controllable manner. Since the sub-micron size objects dispersed in liquid suffer from Brownian motion,such fields may assist to control its influence at will. In our experiments the periodic field is obtained by interference of co-propagating non-diffracting beams and counter-propagating non-diffracting and even evanescent fields. These types of trapping fields enable spatial organization of submicrometer-sized objects into one-dimensional arrays containing even thousands of objects, their controlled delivery over a distance of 1 mm, their sorting according to the size of refractive index. Moreover, the particle tracking enables to study the Brownian dynamics, jumps between neighboring optical traps and interactions between the objects.