  We report the laser cooling and trapping of neutral potassium on an open
transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the
closed 4S-4P transition at 767 nm and then transferred, with unit efficiency,
to a MOT on the open 4S-5P transition at 405 nm. Because the 5P state has a
smaller line width than the 4P state, the Doppler limit is reduced. We observe
temperatures as low as 63(6) microkelvin, the coldest potassium MOT reported to
date. The density of trapped atoms also increases, due to reduced temperature
and reduced expulsive light forces. We measure a two-body loss coefficient of 2
x 10^-10 cm^3/s, and estimate an upper bound of 8x10^-18 cm^2 for the
ionization cross section of the 5P state at 405 nm. The combined temperature
and density improvement in the 405 nm MOT is a twenty-fold increase in phase
space density over our 767 nm MOT, showing enhanced pre-cooling for quantum gas
experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of
bosonic 41K.
