Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications

The paper presents a calibration of the ratio of two-photon absorption cross sections, $\sigma^{(2)}_{Xe}/ \sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100\% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$\cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $\sigma^{(2)}_{Xe}/ \sigma^{(2)}_O$ was determined.