Efficient ionization of atomic tin assisted by N-type multiphoton Raman resonances

We report on the experimental results for laser ionization spectroscopy of atomic tin using a four-color three-step laser ionization scheme in conjunction with an atomic beam apparatus. Typically, the laser ionization efficiency is remarkably limited for certain elements whose thermal population is distributed over its higher lying components of the fine structure at high temperature (e.g. about 2000 K). We demonstrate that the laser ionization efficiency can be increased by simultaneous excitation from the ${}^3{\text{P}}_0$ and ${}^3{\text{P}}_1$ fine-structure components of the 5s²5p² ground-state of atomic tin. This was achieved using two lasers, operating at 283 nm and 301 nm. Furthermore, four-level N-type mutiphoton Raman resonances in this four-color ionization scheme can be utilized to enhance the ionization efficiency allowing an additional ionization process from the third ground state $5s^2$$5p^2$ ${}^3{P}_2$.