OPTICAL TRAPPING OF RAYLEIGH PARTICLES USING A GAUSSIAN STANDING-WAVE

We suggest a modification of a single beam optical trap which enables more effective axial trapping of nanoparticles. We employed interferen ce of an incident wave and the wave which is reflected by the bottom o f the trapping cell to create a standing wave trap. The scattering for ce is strongly suppressed for a highly reflective surface in this conf iguration and consequently the axial force is represented only by the axial gradient force. The main advantage of the standing wave set-up i s that it produces a much stronger axial gradient force than the singl e beam trap, even without high N.A. focusing optics. The trap is less than four times deeper than the single beam one produced by a laser of the same power so that smaller particles could be trapped in the vici nity of an array of stable positions separated by lambda/2 along the b eam axis. Even the axial trap stiffness is several orders higher than in the single beam trap. (C) 1998 Elsevier Science B.V. All rights res erved.