Single-Particle Dichroism Using Orbital Angular Momentum in a Microwave Plasmonic Resonator

Dichroism measurement is mostly restricted to extensive numbers of molecules due to weak response from a single deep-subwavelength particle, and hence single-molecule dichroism is of essential importance for the in-depth study of enantiomers. This paper reports the dichroism capability of a single chiral particle within the diameter of 1/150 wavelengths and smaller, using sharp resonance dips of confined orbital angular momentum (OAM) modes, which are ultrasensitive to disturbance from chiral particles. The OAM modes are realized in a microwave plasmonic resonator via chiral symmetry breaking in the structure. Full-wave simulations and OAM density analysis of the resonant modes confirm the single-particle dichroism principle. Experimental results agree well with the simulations. The principle is demonstrated in the microwave frequency for convenient manipulations and intensive investigations, while it envisions ground-breaking applications of the confined OAM modes in on-chip single-molecule dichroism in the optical frequency range.