Temporal evolution of two-photon time-resolved optogalvanic signals of neon in the 600–630 nm region

Time-resolved optogalvanic (OG) signals of six two-photon transitions of neon were studied in the 600–630 nm region to 2p54d[5/2]2, 2p54d[3/2]2, 2p54d[3/2]1, 2p54d[1/2]1 and 2p55s′[1/2]1 states from the allowed states of the 2p53s configuration (2p53s[3/2]1 and 2p53s′[1/2]0 states). The OG signals were recorded over a range of discharge currents from 2 to 10 mA. The decay rates of the upper and lower states were obtained by fitting the waveforms with the Han et al.’s mathematical rate equation model considering the three states contributing to the signal. Based on the values of decay rates of the upper states, it was proposed that, after excitation to 5s and 4d states, neon atoms radiatively decay to the lumped relevant electronic states of the 2p53p and 2p54p configurations which have the main contribution in producing the OG signals. It was found that, the decay rates of the upper states (the lumped relevant electronic states of 2p53p and 2p54p configurations) increase linearly and slowly with the discharge current for all the transitions considered in this work. The effective decay rates of the upper states and their electron collisional ionization rate parameters were also obtained. This study showed that the dominant relaxation process in the de-population of the upper states is the lengthened radiative decay in plasma medium after laser excitation.