Search for: All records

This is an Editor-in-Chief invited "View and Perspective", which gives a commentary on a recent publication in optical trapping and provides some perspectives of the emerging field of light force. 

Sea-spray aerosols (SSAs) contribute to atmospheric loading, bringing toxic compounds like mercury (Hg) to the atmosphere, affecting the climate and human health. Despite their importance, the investigation into surface modification, including heterogeneous chemical and photochemical reactions of SSAs, is limited. In this work, we studied the heterogeneous chemistry and photochemistry of a single suspended SSA particle and a SSA containing Hg(II) in a reactive environment using optical trapping – Raman spectroscopy. The experiments are focused on the study of hygroscopicity, heterogeneous chemical reaction with ozone (O3), photochemical reaction with UVC radiation of an optically suspended single SSA particle, and photo-reduction of Hg(II) in SSAs under UVC radiation. Results show different Raman signal responses of a single SSA particle when it is optically trapped in air under varying relative humidity conditions as the aerosol particle uptakes and loses liquid water from the surrounding environment. The state and size of the aerosol are determined through the on-time images and different single-particle Raman spectral features. Results also show that the formation of chlorate (ClO3−) is a reaction product of the heterogeneous reaction between the SSA particle and O3. The photochemical reaction products, as the SSA particle suspended in air under UVC radiation, are ClO3− and perchlorate (ClO4−). Further, we observed that these reactions occur only on the surface of the SSA particle. Based on the results, we hypothesize that Hg(II) can be photo-reduced to Hg(I) in SSAs through UVC radiation, and the amount of Hg(I) in SSAs is minor and balanced between the photo-oxidation and photo-reduction reactions. 

We report the experimental realization of optical trapping and controlled manipulations of single particles of arbitrary properties, e.g., nano- to micrometer in size, transparent spheres to strongly light absorbing nonspherical particles, in low-pressure rf plasmas. First, we show optical trapping and transport of single particles in an unmagnetized rf plasma. Then, we show similar observations in a weakly magnetized rf plasma. This is the first demonstration of actively transporting (pushing and pulling) light-absorbing, nonspherical single particles in plasmas. The result suggests that optically trapped, actively controlled, single plasma dust particles (not limited to those externally sampled spheres) could be an in situ micro-probe for dusty plasma and magnetized dusty plasma diagnostics.