Laser-Induced Forces in Metallic Nanosystems: The Role of Plasmon Resonances

Abstract

We present calculations of the laser-induced force between metallic nanospheres, similar and dissimilar in character, and that between a metallic nanosphere and a planar surface. When the separation between these objects is in the 0.5-2 nm range, we find very strong resonances in the laser-induced force associated with excitation of plasmon resonances. Measurement of such forces will provide direct access to the plasmon enhancements of laser fields so critical to optical spectroscopy in the nanoenvironment.

Resonant optical gradient force interaction for nano-imaging and -spectroscopy

“…We can also compare the optical gradient force to the van der Waals force of a sphere-plane geometry, which has a z 1 2 distance dependence in comparison to the z 1 4 of optical gradient force at long distance [32,57]. The optical gradient force is typically weaker than the van der Waals force at short distances, however, under plasmonic resonances the optical gradient force can exceed the van der Waals force [29,32].…”

“…Since the radius of the tip apex  r 10 nm is much smaller than the laser wavelength λ, the nearfield tip and sample interaction under plane wave illumination can be analyzed in the quasistatic approximation by assuming the probe to be a polarizable sphere with radius r. The resulting field distribution on the sample can be effectively reduced to an image sphere of radius r, as shown in figure 1(a). This coupled nanoparticle geometry has been used extensively and with great success, predicting general behaviors accurate to within an order of magnitude [4,5,29]. While the exact geometry of tip and sample affects both the details of magnitude and spectral response of the optical gradient force [49,50], especially for strong polaritonic resonances, the limiting case of two finite spheres provides enough general insight into the spectral variation of the force spectrum and its distance dependence.…”

“…However, despite several theoretical studies [4,[21][22][23][24][25], these works provided limited insight into the spectral characteristics of the optical gradient force and its dependence on electronic and vibrational material resonances of the sample. While the frequency dependence of the optically induced force is often explored in optical trapping of micro-/nanoparticles [5,[26][27][28][29][30][31][32], and in the optically induced mechanical response of plasmonic structures [33,34], the extension for spectroscopic nano-imaging was not explored.…”

Laser Trapping of Colloidal Metal Nanoparticles

“…There have so far only been a few experimental studies concerning metal colloids, 24,44,46 but several theoretical investigations of such effects have been reported in the literature. 37,41,[47][48][49][50][51][52][53][54][55][56][57] For example,…”

Strong Light-Induced Negative Optical Pressure Arising from Kinetic Energy of Conduction Electrons in Plasmon-Type Cavities

“…We will show that a very simple system can display light-induced resonance that is not only large in magnitude, but also attractive rather than repulsive. This will provide a new platform to realize giant optical forces, in addition to micro-or nanosystems such as photonic crystals [11][12][13], plasmonic structures [14][15][16][17], microcavities and waveguides [18][19][20].…”