Near-field optical trapping in a non-conservative force field

Abstract

The force-field generated by a near-field optical trap is analyzed. A C-shaped engraving on a gold film is considered as the trap. By separating out the conservative component and the solenoidal component of the force-field using Helmholtz-Hodge decomposition, it was found that the force is non-conservative. Conventional method of calculating the optical potential from the force-field is shown to be inaccurate when the trapping force is not purely conservative. An alternative method is presented to accurately estimate the potential. The positional statistics of a trapped nanoparticle in this non-conservative field is calculated. A model is proposed that relates the position distribution to the conservative component of the force. The model is found to be consistent with numerical and experimental results. In order to show the generality of the approach, the same analysis is repeated for a plasmonic trap consisting of a gold nanopillar. Similar consistency is observed for this structure as well.

Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling

“…Such an experiment would provide, conversely, nanoantenna-enhanced demagnetization. Further direction to explore could be the study of all-optical switching behaviour assisted by other plasmonic systems providing tight electromagnetic fields nanoconfinement, for instance C-structures 34,35 or Archimedean spirals 36 that focus incident electric fields tightly enough to create force gradients.…”

Modeling Brownian Microparticle Trajectories in Lab-on-a-Chip Devices with Time Varying Dielectrophoretic or Optical Forces

“…Here, is the depth of the volume density of the potential well (i.e., depth of the potential well normalized with respect to particle volume), is the radius of a particle, is representative of the width of the well, and r is the radial distance from the trap center (assumed to be at the origin) to the particle position. The corresponding force profile, , is given by [ 7 , 34 ]: …”

“…Trapping and manipulating small-sized samples are often a key feature of LOCs. On-chip manipulation of micro-sized samples (or microparticles) is usually accomplished by using viscous drag forces applied through fluid flow along with dielectrophoresis (DEP) [ 3 , 4 , 5 ] or optical [ 6 , 7 , 8 ]/ optoelectronic [ 9 , 10 , 11 ] techniques (DEP is more widely used). LOCs can have integrated micro-electrodes and microfluidic channels to carry out these functions [ 12 ].…”

Plasmonic tweezers: for nanoscale optical trapping and beyond

“…17a, b) 319,320 . Numerical simulations were used to determine the optical force and potential well of the plasmonic traps [321][322][323][324] , and a further analysis was performed with the use of dielectrophoresis 325 . Owing to the nature of near-field plasmonic traps, two-dimensional arrays of such traps can be made for complex manipulation and transport of nanoparticles.…”