The BBO crystal developed in recent years possesses good UV properties. The radiation of 204.8nm was obtained by K. Kato` with frequency doubling. We get the tunable radiation from 200nm to 218nm by mixing the second harmonics of 492nm to 550nm with 1064nm using BBO crystal. The fifth harmonic of 1064nm at 213nm is gotten in the same time, and the conversion efficiency from the fourth harmonic, 266nm, to the fifth is up to 48x.
"Tunable UV generation in BBO short to 200nm", Proc. SPIE 1230, International Conference on Optoelectronic Science and Engineering '90, 12303U (1 July 1990); doi: 10.1117/12.2294775; https://doi.org/10.1117/12.2294775