Single-Shot Orientation Imaging of Nanorods Using Spin-to-Orbital Angular Momentum Conversion of Light

TL;DR

This paper introduces a novel single-shot optical imaging technique that uses spin-to-orbital angular momentum conversion to determine the in-plane orientation of nanorods with high accuracy, enabling real-time monitoring of nanoscale rotations.

Contribution

The authors develop a new wide-field, single-shot method for imaging nanorod orientations by encoding their angles into geometric phases of scattered light and converting spin to orbital angular momentum.

Findings

Achieved 2.5° measurement accuracy for nanorod orientation.

Successfully imaged both immobilized and moving sub-100 nm nanorods.

Calibrated method using lithographically fabricated nanorods.

Abstract

The key information about any nanoscale system are orientations and conformations of its parts. Unfortunately, these details are often hidden below the diffraction limit and elaborate techniques must be used to optically probe them. Here, we present a single-shot imaging technique allowing time-resolved monitoring of rotation motion of metal nanorods, realized in a wide-field regime and with no ambiguity of the measured angles. In our novel method, the nanorod orientation is imprinted onto a geometric phase of scattered light composed of the opposite spin states. By spin-to-orbital angular momentum conversion, we generate two oppositely winding helical waves (optical vortices) that are used for restoring the nanorod in-plane orientation. The method was calibrated using lithographically fabricated nanorods and tested by the rotation imaging of immobilized and moving sub-100 nm colloidal nanorods (measurement accuracy of 2.5{\deg}). We envision this technique can be used also for estimation of nanorod aspect ratios and their out-of-plane orientations.