Towards time-resolved measurements of solvated electrons at the plasma/liquid interface

Contamination of groundwater by poly-fluoroalkyl substances (PFAS) is increasingly recognized as a major environmental issue. These compounds bioaccumulate, can cause adverse health outcomes, and are difficult to break down. Low temperature plasma (LTP) offers promising avenues to remediation of contaminated liquids, but many mechanisms remain to be understood. For PFAS, dissolved free electrons ("solvated electrons") may be a key part of effective plasma treatment. To provide insight into relevant processes, we are developing a broadband transient absorption diagnostic to measure the concentration of solvated electrons at a liquid surface. We use light from a sub-nanosecond, pulsed supercontinuum (FYLA Iceblink) and the total internal reflection geometry of Rumbach, et. al (2015) to sample a broad absorption feature in the thin layer immediately underneath the liquid surface. Low-jitter timing allows us to localize the measurement relative to the start of the discharge, and multi-channel lock-in detection allows access to the small signal. We will describe the current diagnostic design, results to date, and planned improvements.