Enhanced optical pressure with asymmetric cavities

Asymmetry in a one-dimensional optical Fabry-Perot cavity is shown to produce a large net pressure, the total on the two mirrors. Consequently, asymmetric cavity structures that are formed in this manner can experience a net force that is greater than that resulting from the excitation light illuminating a perfect mirror. The conditions for this to occur are a modest quality factor regime, where some influence of the cavity is needed, but when the quality factor becomes very large the enhancement diminishes. This result is used to illustrate how structuring a metal surface, thereby forming a plasmonic cavity, can substantially increase the optical pressure over that possible with a planar interface. It is shown that the force on one mirror in an asymmetric arrangement can be increased relative to the other. Importantly, the sum of the pressures on both mirrors increases through asymmetry and with quality factor, while adhering to conservation of energy. Using cavity quality factor as a measure, the one-dimensional Fabry-Perot cavity pressure results are related to pressure enhancement with a structured metal surface where a different type of mode in an asymmetric cavity is excited, the lowest order metal-insulator-metal surface plasmon mode. In principle, an optical cavity or cavity array formed with any material should display this enhanced pressure phenomenon. The length scale of the resonant structures for visible light can be as small as a few tens of nanometers, in the case of metals. With this understanding guiding the design of structured metallic and dielectric materials, a many-fold increase in pressure over that on a perfect mirror is possible. Consequently, the relatively weak optical force can become more effective in a variety of scientific and technological applications. © 2019 American Physical Society.