2-photon ionization for efficient seeding and trapping of strontium ions

We describe an efficient way to photoionize strontium atoms in a linear radio-frequency trap. We use a 2-photon second order process to excite the autoionization resonance (4d²+5p²) ¹D₂ in neutral strontium (Sr). A doubled Ti:sapphire laser system is used at 431 nm to provide 100 fs pulses at 82 MHz. The fabrication of the laser systems for addressing the Sr⁺ transitions necessary for laser cooling and excitation of quantum jumps, vacuum system and ion trap structure are also described. With the current setup a easy and repeatable trapping of linear ion chains is readily achieved at very low Sr vapor pressures.