|Artistic rendering of a lithography by photonic nanojets from an optically trapped microsphere. Courtesy: A A R Neves|
Traditional optical tweezers, which have been around for decades, are one of the most important modern-day tools in biology, physics and chemistry. They work by trapping micron-scale objects near the focus of a laser beam. The technique allows objects to be picked up and moved to another place using just light.
Being able to control the position of individual molecules in this way is critical in medical research, for example, when manipulating viruses or large proteins. And being able to accurately place tiny objects, such as carbon nanotubes or nanowires, for instance, in a given structure or array will be important for fabricating nanomachines such as molecular motors and other devices in the future.
Nanojets are relatively new structures and are typically formed under the “shadow” of an illuminated dielectric cylinder or microsphere. The microsphere acts as a focusing lens and the nanojets form thanks to the constructive interference between the incoming and scattered light fields.
The nanojets created by Antonio Alvaro Ranha Neves of the Centro de Ciências Naturais e Humanas at the UFABC are a little more complex since they rely on highly focused incident light beams (in contrast to the plane waves generally used to form such jets). Neves used two collinear and co-propagating beams to create his nanojets and positioned one trap in a particular direction with respect to the other. It is the precise positioning of these two beams in this way that allows the nanojets to be switched on and off at will, he explains When they are switched on, they exert a trapping force on the microsphere, holding it approximately midway between the focuses of both beams.
Nanotechweb: Optical tweezers produce “nanojets”, Belle Dumé