Continuous counting, sizing and refractive index measurement of airborne particles in hollow-core photonic crystal fibre

摘要

Air pollution by particles of aerodynamic diameter less than 2.5 μm (PM_(2.5)) is currently an important environmental issue. As standard methods for monitoring and characterization are time-consuming and expensive, there is need for a simple, effective and inexpensive device for real-time PM_(2.5) monitoring. Although optical methods based on the scattering of laser beams exist, they do not provide independent measurement of particle size and refractive index. In systems based on detection in an evanescent optical field, particles tend to adhere to the surface, strongly limiting the device lifetime. Here we report a new approach to airborne particle characterization that makes use of hollow-core photonic crystal fibre (HC-PCF). Employing optical gradient and radiation forces to trap and propel airborne particles along the hollow core, it provides in situ particle counting, sizing and refractive index measurement in real-time with effectively unlimited device lifetime. We show that the transmission drop and time-of-flight can be unambiguously mapped to particle size and refractive index.