Compact cavity-enhanced aerosol detector using incoherent light sources

We have realized a compact optical particle counter utilizing enhancement of light scattering within a high finesse Fabry-Perot optical cavity. In contrast with laser-based approaches such as cavity ringdown spectroscopy, we use the light stream from superluminescent and light-emitting diodes that have no longitudinal coherence. This eliminates the vibration sensitivity that is typical of laser-based cavity methods. The use of the transmission mode of detection allows us to reduce the cavity mirror separation to below 1 cm, with no obvious limit to miniaturization. Typical light scattering instruments are larger, in part due to their sensitivity to background signals from the light source. Our approach paves the way toward what we believe to be is a new generation of compact and portable instruments. A simultaneous comparison of the scattering signals with a commercial particle counter suggests that our cavity may be sensitive to ultrafine particles below 300 nm diameter, which are typically not recorded in such counters.