Polarization-switchable plasmonic emitters based on laser-induced bubbles

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 (n=1.0) in water (n=1.333) to obtain a large index variation as high as vertical bar Delta n vertical bar=0.333, the emission polarization of an ultra-small plasmonic emitter (similar to 0.4 lambda(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 s(x)=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 (vertical bar Delta n vertical bar=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 Delta gamma approximate to 0.66.