Ricerc@Sapienza

Optical tweezers were introduced by Askhin in 1986, when he proposed a way for capturing particles by means of focalized light, through the mechanism of optical trapping. Over the years, optical tweezers have assumed a prominent role in scientific research, covering the most disparate fields, from physics to biology and materials nano-engineering. For this reason, Askhin was awarded the Nobel Prize in 2018. At the same time, over the last decade multimode optical fibres have attracted a growing interest, thanks to the possibility of propagating high power laser beams, thus unveiling previously unforeseen nonlinear effects.

SPOTLIGHT aims at merging these two major branches of research, by proposing optical fibres as a new practical tool for generating microstructured light for 3D nonlinear optical trapping applications.

Our project is based on the exploitation of a recent discovery by the PI and his coworkers: the emission of a beam with a spiral shaped intensity profile in the far-field from the output facet of an optical fibre. Such a spiral emission is only obtained for proper laser-fibre coupling conditions, so that the beam propagating inside the fibre carries unconventional longitudinal orbital angular momentum (OAM). Although spiral emission is a linear phenomenon, i.e., it can be achieved with low power light sources, it is subject to nonlinear effects when high intensity lasers are used. Specifically, the interplay of radial self-phase modulation, Imbert-Fedorov shift and supercontinuum generation leads to spatial self-organization in the optical frequency domain, or rainbow-like spiral emission.

The main goal of SPOTLIGHT is developing a 3D optical trapping device, which exploits rainbow spiral emission. This will lead to breakthrough advantages in optical trapping, leading to a significant improvement of the optical tweezers technology, such as for example a new class of micromixers, which will find application in medicine and nano-bioengineering.