Time-Selective TALIF Spectroscopy of Atomic Oxygen Applied to an Atmospheric Pressure Argon Plasma Jet

Two-photon laser excitation diagnostics is applied to characterize the atomic oxygen production in an atmospheric pressure Ar+O
₂
% plasma jet. The plasma jet device is driven by a 13.56-MHz radio-frequency power supply. It is found that in addition to the fast decaying two-photon absorption laser-induced fluorescence (TALIF), unexpected emissions from excited atomic argon and oxygen species with a long decay time are existent in TALIF processes. This phenomenon is believed to be common in TALIF diagnostics of atomic oxygen, especially in high-pressure plasmas because of intense collisional energy transfer processes. In order to avoid the influence of extra emissions on TALIF performance, time-selective detection is utilized to capture the pure atomic oxygen fluorescence through nanosecond imaging for characterizing the spatial distribution of O atoms in the plasma effluent. An approximate method for the absolute density calibration based on the atomic oxygen fluorescence in the open air, due to the laser-induced photodissociation of O
₂
molecules, is applied to the TALIF signal from a plasma jet. The 2-D spatial distributions of the ground state density of atomic oxygen are built in the plasma effluent under different O
₂
contents. With the increase in O
₂
admixtures, the generation of atomic oxygen is constricted to the plasma core area close to the gas outlet, and a maximum O density is obtained with 0.3% O
₂
in the core area.