Calculation of the spatial resolution in two-photon absorption spectroscopy applied to plasma diagnosis

Abstract

© 2014 AIP Publishing LLC. We report a detailed characterization of the spatial resolution provided by two-photon absorption spectroscopy suited for plasma diagnosis via the 1S-2S transition of atomic hydrogen for optogalvanic detection and laser induced fluorescence (LIF). A precise knowledge of the spatial resolution is crucial for a correct interpretation of measurements, if the plasma parameters to be analysed undergo strong spatial variations. The present study is based on a novel approach which provides a reliable and realistic determination of the spatial resolution. Measured irradiance distribution of laser beam waists in the overlap volume, provided by a high resolution UV camera, are employed to resolve coupled rate equations accounting for two-photon excitation, fluorescence decay and ionization. The resulting three-dimensional yield distributions reveal in detail the spatial resolution for optogalvanic and LIF detection and related saturation due to depletion. Two-photon absorption profiles broader than the Fourier transform-limited laser bandwidth are also incorporated in the calculations. The approach allows an accurate analysis of the spatial resolution present in recent and future measurements.The present work was supported by the DGICYT (Ministerio de Educacion Cultura y Deporte) Contract Reference No. FIS2007-62604 and by DGICYT (Ministerio de Economıa y Competitividad) Contract Reference No. ENE2012-35902 and FEDER funds.Peer Reviewe