# On-the-fly particle metrology in hollow-core photonic crystal fibre

## TL;DR

This paper introduces a novel in situ particle metrology technique using hollow-core photonic crystal fibre, enabling real-time airborne particle counting, sizing, and refractive index measurement with high accuracy and unlimited device lifetime.

## Contribution

The authors develop a new optical method leveraging hollow-core photonic crystal fibre for real-time, in situ airborne particle analysis, overcoming limitations of existing optical techniques.

## Key findings

- Achieves unambiguous particle size and refractive index measurement.
- Provides real-time monitoring suitable for open atmosphere and enclosed environments.
- Offers effectively unlimited device lifetime due to particle capture mechanism.

## Abstract

Efficient monitoring of airborne particulate matter (PM), especially particles with aerodynamic diameter less than 2.5 um (PM2.5), is crucial for improving public health. Reliable information on the concentration, size distribution and chemical characteristics of PMs is key to evaluating air pollution and identifying its sources. Standard methods for PM2.5 characterization require sample collection from the atmosphere and post-analysis using sophisticated equipment in a laboratory environment, and are normally very time-consuming. Although optical methods based on analysis of scattering of free-space laser beams or evanescent fields are in principle suitable for real-time particle counting and sizing, lack of knowledge of the refractive index in these methods not only leads to inevitable sizing ambiguity but also prevents identification of the particle material. In the case of evanescent wave detection, the system lifetime is strongly limited by adhesion of particles to the surfaces. Here we report a novel technique for airborne particle metrology based on hollow-core photonic crystal fibre. It offers in situ particle counting, sizing and refractive index measurement with effectively unlimited device lifetime, and relies on optical forces that automatically capture airborne particles in front of the hollow core and propel them into the fibre. The resulting transmission drop, together with the time-of-flight of the particles passing through the fibre, provide unambiguous mapping of particle size and refractive index with high accuracy. The technique represents a considerable advance over currently available real-time particle metrology systems, and can be directly applied to monitoring air pollution in the open atmosphere as well as precise particle characterization in a local environment such as a closed room or a reaction vessel.

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Source: https://tomesphere.com/paper/1907.09469