Resonance ionization spectroscopy of sodium Rydberg levels using difference frequency generation of high-repetition-rate pulsed Ti:sapphire lasers

The generation of tunable laser light in the green to orange spectral range has generally been a deficiency of solid-state lasers. Hence, the formalisms of difference frequency generation (DFG) and optical parametric processes are well known, but the DFG of pulsed solid-state lasers was rarely efficient enough for its use in resonance ionization spectroscopy. Difference frequency generation of high-repetition-rate Ti:sapphire lasers was demonstrated for resonance ionization of sodium by efficiently exciting the well-known D₁ and D₂ lines in the orange spectral range (both ≈0.28em0ex589 nm). In order to prove the applicability of the laser system for its use at resonance ionization laser ion sources of radioactive ion beam facilities, the first ionization potential of Na was remeasured by three-step resonance ionization into Rydberg levels and investigating Rydberg convergences. A result of EIP=41449.455(6)ₛₜₐₜ(7)sys0.28em0excm^-1 was obtained, which is in perfect agreement with the literature value of EIPˡⁱᵗ=41449.451(2)0.28em0excm^-1. A total of 41 level positions for the odd-parity Rydberg series nf4pt0ex²F5/2,7/2ᵒ for principal quantum numbers of 10≤n≤60 were determined experimentally.