An experimental setup for investigations of two-colour multiphoton ion
ization in alkali atoms is described. It consists of two tunable dye l
asers pumped by the Nd:YAG nanosecond laser, source of atomic beam and
ion detection system. The setup has been tested on two-colour three-p
hoton ionization of potassium near the 4S(1/2)-->4P(3/2)-->5D(3/2,5/2)
resonance.