Four yeast cells (approximately 6-8 micm in size) are trapped in the standing wave created by 99% retro-reflected focused Gaussian beam incident perpendiculary to the screen plane. The standing wave enables trapping of multiple objects in the vertical direction. Cell No. 1 is trapped above the cell No. 2 (a). The cell No. 3 enters the trap and stays there (b-c). Three cells are trapped in the vertical line and are moved near the fourth one (d).

Trapping of two 100 nm particles in the standing wave trap visualized by dark-field illumination. Reflectivity of the dielectric mirror was 99%. Even though the numerical aperture of the objective was just 0.6, strong axial gradient force enables 3D trapping of two particles. Part (a) shows one particle in the trap, the second one is approaching the trap in (b) and both followed horizontal motion of the optical trap in part (c).

Example that even weakly reflective mirror (ordinal water-glass interface with reflectivity 0.4%) creates standing wave strong enought to confine in 3D 100-nm polystyrene particles.  (a) Two 100-nm sheres, 1 and 2, trapped approximately 1 micm above the bottom. (c) Particle 3 consequently enters the trap and moves simultaneously with the other two trapped particles. (d) Finally, the trapping beam is switched off and the particles left the trap in random directions.