An international research team discovered a new type of curved light beams, dubbed a “photonic hook”. Photonic hooks are unique, as their radius of curvature is two times smaller than their wavelength. This is the smallest curvature radius of electromagnetic waves ever recorded. Photonic hook can improve the resolution of optical systems and control the movement of nanoparticles, individual cells, viruses or bacteria.
Results of this research were published in Optics Letters (“Photonic hook: a new curved light beam”) and Scientific Reports (“‘Photonic Hook’ based optomechanical nanoparticle manipulator”).
For the longest time, physicists claimed that electromagnetic radiation propagates along a straight line; however, in 2007 the existence of a curved electromagnetic ray was experimentally confirmed. It was dubbed the “Airy beam” and, up until now, was considered a singular example of a curved ray. Recently, scientists from ITMO University, along with their colleagues from Tomsk State University, the University of Central Florida, the University of Ben-Gurion and the University of Bangor, have discovered a new type of curved light beam – the photonic hook.
“Photonic hook is formed when we direct a plane light wave to a dielectric particle of an asymmetric shape,” says Alexander Shalin, head of the International Laboratory of Nano-opto-mechanics at ITMO University. “We studied a particle called cuboid. It has the appearance of a cube with a prism located on one side. Due to this shape, the time of the complete phase of the wave oscillations varies irregularly in the particle. As a result, the emitted light beam bends.”
Scientists showed that the photonic hook’s curvature radius can be much smaller than its wavelength. The curvature can also be adjusted by varying wavelength, incident light polarization as well as geometric parameters of the emitting particle. This property can be used to redirect an optical signal, to overcome the diffraction limit in optical systems or to move individual particles on a nanoscale.