Electromagnetic forces in photonic crystals and in metamaterials*

We investigate numerically the electromagnetic forces induced by a beam of light incident on a thin slab of (i) a photonic crystal (dielectric or metallo-dielectric) and (ii) a metamaterial of negative dielectric properties (negative index n, or individually negative permittivity and/or permeability). For photonic crystals, light excitation of the Mie and/or plasmon resonances of the individual ``atoms'' results in strong forces between the crystal layers. The influence of the band gaps on the forces is also discussed. For metamaterials, the interface forces (on either side of the slab) display an interesting spectrum associated with negative dielectric properties. In both systems, resonant dielectric behavior leads to strong field enhancement, large field gradients, and, consequently, strong electromagnetic forces. We also look at the forces between two slabs of metamaterial, or between alternating slabs of metamaterial and photonic crystal. Our calculations invoke the transfer matrix and FDTD algorithms, and we believe should prove relevant in the manipulation of nanoscale objects by laser light.