Phase-controlled propagation of surface plasmons.

Directional emission of electromagnetic radiation can be achieved using a properly shaped single antenna or a phased array of individual antennas. Control of the individual phases within an array enables scanning or other manipulations of the emission, and it is this property of phased arrays that makes them attractive in modern systems. Likewise, the propagation of surface plasmons at the interface between metal films and dielectric materials can be determined by shaping the individual surface nanostructures or via the phase control of individual elements in an array of such structures.

Demonstration of fold and cusp catastrophes in an atomic cloud reflected from an optical barrier in the presence of gravity.

We experimentally demonstrate first-order (fold) and second-order (cusp) catastrophes in the density of an atomic cloud reflected from an optical barrier in the presence of gravity and show their corresponding universal asymptotic behavior. These catastrophes, arising from classical dynamics, enable robust, field-free refocusing of an expanding atomic cloud with a wide velocity distribution. Specifically, the density attained at the cusp point in our experiment reached 65% of the peak density of the atoms in the trap prior to their release.