Dielectric materials in Optical Traps

[frug]

Why are optical traps constructed using beads that are made of dielectric materials? What property of dielectrics is being employed here? Would a non-dielectric material still experience radiation force from photons?

Thanks!

 

[Andy Resnick]

They don't have to be dielectric- metals can also be trapped.

What is generally done, for a 'vanilla' single-beam trap, is to trap homogeneous dielectric particles with an index of refraction higher than the solvent- the beam is then modeled as a potential well, and the particle 'falls' into the well.

One can use birefringent particles and the trap will exert a torque:

http://chaos.utexas.edu/manuscripts/1236630607.pdf

One can trap conducting particles or particles with a *lower* relative refractive index using, for example, a 'doughnut' mode beam:

http://www.opticsinfobase.org/abstract.cfm?URI=ol-19-22-1807