Detection of Long-Lived Electrons Around CO2-Laser-Produced Plasma in Atmospheric Gases Using Symmetric Double-Probe System

We have studied the behavior of charged particles around a CO₂-laser-produced plasma in atmospheric air using a symmetric double-probe system. It is important and useful to verify the existence of long-lived electrons in applications such as laser-induced electrical discharge, laser-triggered gap switching, and laser ablation. Experimental results showed that 1) electrons and plasma can be discriminated based on their time of arrival by applying intermittent pulses with biases less than the electron affinities of negative ions (O^- or O₂ ^- ); 2) the electron signal responded for more than 100 , even though the electrons were influenced by a strong attachment effect that is induced by oxygen and water molecules that are present in room air at 1 atm; and 3) the total density of free and detached electrons around the laser-produced plasma was estimated to be 10¹⁶ m^-3 based on the pulse signal response that is detected by double-probe electrodes.