Opto-mechanical force measurement of deep sub-wavelength plasmonic modes

Spatial mapping of optical force near the hot-spot of a metal-dielectric-metal bow-tie nanoantenna at a wavelength of 1550 nm is presented. Non contact mode atomic force microscopy is used with a lock-in method to produce the map. Maxwell’s stress tensor method has also been used to simulate the force produced by the bow-tie and it agrees with the experimental data. If dual lock-in amplifiers are used, this method could potentially produce the near field intensity and optical force map simultaneously, both with high spatial resolution. Detailed mapping of the optical force is critical for many emerging applications such as plasmonic biosensing and optomechanical switching.