Multiwalled carbon nanotubes on aluminum or indium tin oxide layers were irradiated with gallium focused ion beams (FIBs) to induce defects and increase emission sites of carbon nanotubes (CNTs). A turn-on voltage was found to decrease from 460 to 220 V by ion irradiation at a dose of 1 x 10(15)/cm(2), corresponding to turn-on fields from 3.7 to 1.8 V/mum. However, noticeable improvements in emission characteristics were not observed as a result of high-dose FIB irradiation at and above 1 x 10(16)/cm(2). Because of the local temperature rise due to the intense FIB this irradiation resulted in. melting of CNTs. The third harmonic of a neodymium-doped yttrium fluoride (Nd:YLF) laser. light was irradiated over screen-printed CNT cathodes, which resulted in turn-on voltage decreasing from 400 to 320 V, corresponding to turn-on fields from 3.2 to 2.6 V/mum, with increased emissions by a factor of 6. (C) 2003 American Vacuum Society.