Imaging of Methyl and Hydrogen Peroxide in Low Temperature Plasmas by Photofragmentation Laser-Induced Fluorescence

Methyl (CH₃) and hydrogen peroxide (H₂O₂) are key reactive species in plasma assisted processes such as catalysis, combustion, surface decontamination, and biomedical treatments. Imaging of CH₃ and H₂O₂ is challenging because they cannot be detected directly by laser-induced fluorescence. We present recent developments in a technique for imaging 2D distributions of these species in plasmas using photofragmentation laser-induced fluorescence (PF-LIF). The target molecule, CH₃ or H₂O₂, is photodissociated by a UV pump laser to produce CH or OH fragments, respectively. These photofragments are then detected with LIF imaging using an overlapping probe laser beam for LIF excitation. Our recent work further develops the PF-LIF technique to enable measurements in a wider range of plasma conditions, such as plasmas with spatially and temporally varying collisional quenching environments. We demonstrate PF-LIF imaging measurements of CH₃ in plasma-assisted flame stabilization, with quantification of the PF-LIF signals facilitated by complementary coherent anti-Stokes Raman scattering (CARS) temperature measurements. We also demonstrate CH₃ imaging in a pulsed He plasma jet interacting with a CH₄ bath gas. We investigate H₂O₂PF-LIF imaging measurements in an RF plasma jet and address possibilities for detection of HO₂.