From zero to breakdown: Using optical tweezers to simultaneously trap, charge and measure the charge of a microparticle in air

Charge accumulation on aerosol particles, e.g. dust, volcanic ash or cloud ice, plays a critical role in a variety of natural and industrial processes [1]. In our experiment, we utilize optical tweezers to levitate individual SiO₂ particles in the micrometer size range and observe their charging and discharging dynamics over days-to-weeks time periods and with elementary-charge resolution. Our approach allows us to study these processes without losing information to ensemble averages or external interference from other particles or substrates [2]. Using two-photon absorption from the trapping laser [3] we can charge the trapped particle at different rates and to different values, observing every charging and discharging event along the way. This new approach lets us watch, in real time, how a micron-scale airborne particle gains and loses charge, observing its electric evolution all the way from the neutral state to its charge limit—the point of electric breakdown. By studying the charging behavior of the particle and the spontaneous discharges it experiences, we hope to contribute to a better understanding of the microphysical processes involved in lightning initiation and adjacent electrical phenomena in the atmosphere.

[1] Zhang L., et al. (2016) Indoor Built Environ 25 (3) 437-440.

[2] Ricci F., et al. (2019) Nano Letters 19, 6711.

[3] Stoellner et al. (2025) Phys. Rev. Lett. (accepted for publication) https://doi.org/10.1103/5xd9-4tjj .