A tunable ultraviolet (UV) laser was used to irradiate the screen-printed carbon nanotube (CNT) samples in air and in high vacuum. UV laser lights with wavelengths of 349 and 266 nm from a tunable laser were used with average energy densities of 20.3, 10.2, and 2.25 mJ/cm(2), respectively, with different irradiation times. The field emission characteristics of the CNT cathodes irradiated in air were drastically improved, whereas those of the samples irradiated in vacuum were slightly improved. Irradiation by a 266 nm laser light resulted in more obvious improvement in the emission characteristics than that by 349 nm. The maximum emission current density at an applied electric field of 6.2 V/mum at an energy density of 20.3 mJ/cm(2) increased from 0.006 to 20.15 mA/cm(2) after laser irradiation with a wavelength of 266 nn, and the turn-on field decreased from 3.7 to 1.2 V/mum. (C) 2003 American Vacuum Society.