Reconfigurable graphene beams for microscopy and micromanipulation
Graphene supports strongly confined surface plasmons at infrared frequencies that can be tuned using a gate voltage. In this work, these surface plasmons will be used to generate reconfigurable, TM-polarized (P-polarized) Bessel beams for microscopy applications and micromanipulation. The reconfigurable Bessel beams could be used
as virtual probes for optical imaging and sensing. Reconfigurability would allow the range of the Bessel beam (stand-off distance in microscopy) to be controlled electronically. In addition, reconfigurable, non-paraxial Bessel beams (tractor beams) could be used to exert varying degrees of negative (pulling) optical force on microparticles. This would allow microparticles to be dragged toward a light source in a controlled manner.
In this work, a cylindrical surface plasmon will be excited on graphene’s surface by a radially-polarized light beam. This surface plasmon will be reflected from a circular boundary (at radius r) on the graphene surface to establish a Bessel field profile. The beamwidth of the Bessel beam will be reconfigured by locally tuning
graphene’s conductivity (within a radius r) using an applied gate voltage. A step discontinuity in applied voltage at a radius r will create a circular boundary on the graphene surface. The cylindrical surface plasmon will reflect off of this boundary to establish the interference pattern needed for a Bessel beam profile. The radius of
this step discontinuity will be varied through a gate bias in order to tailor the truncation of the Bessel beam. The graphene sheet will be on top of the dielectric substrate with gate electrodes on its underside.
This project will be an interdisciplinary effort involving large-area graphene patterning, electromagnetic modeling, and infrared measurement and characterization.