High Efficiency Triple-Helix Solenoid Beam Generated by Dielectric Metasurface

Abstract

Solenoid beams are structured beams exhibiting patterns of light that rotate around the axis of propagation. They can exert forces on objects in a direction opposite to the light propagation direction and are thus referred to as tractor beams. Previous studies have produced solenoid beams using spatial light modulators (SLMs), but cost, weight, and size limit their widespread application. Here, we experimentally demonstrate a silicon metasurface that generates a triple helix solenoid beam. The beam is equivalent to the superposition of Bessel beams with orbital angular momentum (OAM) values of −10 and −7 and internal angles of 0.005 and 0.004 rad, respectively. Our metasurface demonstrates a diffraction efficiency of >90% and a transmission of >75%, a significant improvement over SLMs. We map the beam's intensity profile at up to ∼21 cm from the metasurface, showing its triple helix profile with negligible diffraction. We furthermore experimentally investigate interference between the solenoid beam and a Gaussian beam. This allows us to unravel the OAM information embedded in our two-component solenoid beam.