Tunable ultraviolet radiation in the 200-230-nm region has been genera
ted with beta barium berate crystals by type I sum-frequency mixing of
the second harmonic with the fundamental beam hom a dye laser pumped
by the second harmonic of the same Nd:YAG laser. A noncollinear phase-
matching configuration has made it possible to realize conversion effi
ciency of 21% at 208.3 on with input power densities as low as 28 MW/c
m(2) for the fundamental and 2.4 MW/cm(2) for its second-harmonic radi
ation. The absorption characteristic of a standard DNA sample has been
studied with the generated tunable ultraviolet source, revealing addi
tional features compared with those obtained with a spectrophotometer.
(C) 1998 Optical Society of America. OCIS codes: 190.0190, 190.2620.