Measuring spontaneous discharges of individual aerosol particles with optical tweezers

How is lightning triggered on the microscale? Despite decades of research, this question remains unanswered [1]. In our experiment, we use optical tweezers to gain a better understanding of the microscale physics of electric charging and discharging by levitating individual SiO₂ particles in the micrometer size range and observing 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 the point where it undergoes electric discharge. 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.

Figure 1: Time vs. electric charge curve of a single SiO₂ sphere (d = 0.69 µm) showing spontaneous discharges.

 

This project has received funding from the European Research Council (ERC) under the European Union’s Starting Grant (A. Stoellner, I.C.D. Lenton & S.R. Waitukaitis received funding from ERC No. 949120, C. Muller received funding from ERC No. 805041).

 

[1] Dwyer, J. R., & Uman, M. A. (2014), Physics Reports, 534(4), 147–241.
[2] Ricci, F. et al. (2019), Nano Letters 19, 6711.
[3] Stoellner, A. et al. (2025), Phys. Rev. Lett. 135(21), 218202.