Polarization-switchable plasmonic emitters based on laser-induced bubbles

Abstract

Owing to weak light-matter interactions in natural materials, it is difficult to dynamically tune and switch emission polarization states of plasmonic emitters (or antennas) at nanometer scales. Here, by using a control laser beam to induce a bubble (<i>n</i>=1.0) in water (<i>n</i>=1.333) to obtain a large index variation as high as |Δ<i>n</i>|=0.333, the emission polarization of an ultra-small plasmonic emitter (~0.4<i>λ</i>²) is experimentally switched at nanometer scales. The plasmonic emitter consists of two orthogonal subwavelength metallic nanogroove antennas on a metal surface, and the separation of the two antennas is only <i>s</i><i>_x</i>=120 nm. The emission polarization state of the plasmonic emitter is related to the phase difference between the emission light from the two antennas. Because of a large refractive index variation (|Δ<i>n</i>|=0.333), the phase difference is greatly changed when a microbubble emerges in water under a low-intensity control laser. As a result, the emission polarization of the ultra-small plasmonic emitter is dynamically switched from an elliptical polarization state to a linear polarization state, and the change of the degree of linear polarization is as high as Δ<i>γ</i>≈0.66.