Two-Photon Ionization of Cs₂ in the Wavelength Range 5300–6200 Å

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The relative cross sections of the production of Cs⁺ and Cs₂⁺ ions through the two-photon ionization of Cs₂ were measured in the 5300–6200 Å wavelength range. A linear polarized dye laser was operated in the CW mode as a light source. The results showed that (1) the cross sections for Cs⁺ ions have a broad peak at around 5570 Å and the threshold at around 6010 Å, and (2) those for Cs₂⁺ ions have the largest peak at around 5940 Å and many structures in the wavelength range longer than it. Through consideration of the above results, we suggested that Cs⁺ ions are produced not only by two-photon ionization of Cs₂, but also by a participation of a third photon. The threshold for Cs⁺ ions at around 6010 Å is concerned with the intermediate excited-state Cs₂(C¹Π_u⁺(v′)), which can be excited from the ground state X¹Σ_g⁺(v″=0).