Cost reduction and performance improvement of electric field measurement in plasmas by laser-induced fluorescence-dip spectroscopy

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The objective of this project is to reduce the equipment cost and to improve the data acquisition efficiency of the electric field measurement by laser-induced fluorescence-dip spectroscopy. The research results are summarized as follows. 1) We proposed excitation-observation schemes which are compatible with the use of diode lasers. 2) We analyzed the proposed scheme by rate equations. We found that the intensity of laser-induced fluorescence (LIF) was reduced temporally even when cw diode lasers were used for excitation. We examined the reduction ratio and the duration of the temporal reduction of LIF. 3) We demonstrated a two-step excitation scheme using a pulsed tunable laser and a diode laser. 4) To realize the excitation scheme using two diode lasers, we constructed a spectroscopy system employing a photon counter and an acoustic-optical modulator. 5) We showed the possibility that the less significant reduction LIF in the two-step excitation was attributed to the cascade transition from the laser-excited state. 6) We proposed a two-route scheme as an alternative excitation-observation scheme. We demonstrated the reduction of LIF by the two-route scheme. 7) We proposed an excitation-observation scheme employing a two-step excitation and cavity-ringdown absorption spectroscopy. 8) We demonstrated the enhancement of the data acquisition efficiency by employing a two-dimensional LIF spectroscopy system. 9) We compared the experimentally observed structure of sheathe electric field in an electronegative plasma with a theory based on a fluid model. We summarized the agreement and the discrepancy between the experimental and theoretical results.