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Investigation of two-photon-induced polarization spectroscopy of the a–X ~1,0! transition in molecular nitrogen at elevated pressures

Kaminski, CF; Dreier, T, "Investigation of two-photon-induced polarization spectroscopy of the a-X (1-0) transition in molecular nitrogen at elevated pressures", APPLIED OPTICS 39:1042-1048(2000), DOI:10.1364/AO.39.001042, | pdf


Abstract

Two-photon-induced polarization spectroscopy of molecular nitrogen in the  system near 283 nm was performed, and its signal dependence investigated over the pressure range from 1.2 to 5 bars at 300 K. A significant increase of the signal intensity with pressure beyond the expected square law for a two-photon process was observed for pure nitrogen. Similar behavior was also found for a constant nitrogen partial pressure with increasing partial pressures of argon buffer gas. In both cases the spectral linewidth of the excited transitions increased dramatically with overall pressure. A possible explanation is given for the observed behavior in terms of contributions to the nonlinear susceptibility of the medium from the population of one-photon resonantly absorbing excited-state nitrogen and ground state N2 1 ions created in the multiphoton absorption process at the high laser intensities required.