Key points are not available for this paper at this time.
Two tunable dye lasers have been used to generate coherent radiation at a tunable sum frequency in the vacuum-ultraviolet spectral region. Spectral ranges of 3500 cm^-1 around 1895 and 1200 cm^-1 around 1798 have been covered. These ranges may easily be extended. Large (10^4) enhancements of 2₁+₂ sum mixing are seen when 2₁ is tuned to a double-quantum allowed transition from the ground state in Sr vapor.
Hodgson et al. (1974) studied this question.