Photolysis of caged compounds has become a standard tool for the rapid
application of bioactive molecules. In principle this technique also
allows to apply substances in a spatially very restricted manner. An i
mportant practical limitation for such experiments, however, is the hi
gh cost of UV lasers. Here we describe the assembly of an inexpensive
pulsed nitrogen laser which is suitable for photolysis experiments. Th
e laser which can be constructed in less than 1 week and for less than
US$ 500 emits light pulses with a duration of approximately 5 ns, an
energy of up to 200 mu J ((=) over cap 40 kW) and a wavelength of 337
nm. Its beam can be focused to roughly 30 mu m, a firing frequency of
up to 50 Hz can be achieved, and electrical artifacts are minimal. The
se specifications make the laser optimally suited for most photolysis
experiments. Its low price and ease of use should make the technique o
f spatially restricted flash photolysis amenable to many laboratories.