Optical stacking of microparticles in a pyramidal structure created with a symmetric cubic phase

We show a simple way to generate three dimensional optical potentials consisting of tightly localized high intensity spots arranged in a structure with a pyramidal geometry. The three dimensional patterns are created by focusing a Gaussian beam with a symmetric cubic phase abs((ax)3) + abs((ay)3) imprinted by a spatial light modulator. We show that it is possible to trap and stack around a hundred dielectric microspheres (silica mean diameter 2.47 μm) in pyramidal structures (characteristic dimensions H, W ∼ 15 - 20μm) held together by optical binding with moderate laser power (P < 20 mW). Axial stability is mainly provided by balancing the light scattering force with the axial gradient and gravity. The microparticle structures are sufficiently stable to be easily displaced by moving the microscope stage.