DIAMOND AND RELATED MATERIALS The possibility of laser induced variation of optical and electrical properties of conductive nanocrystalline diamond (CNCD) films has been demonstrated. The films were produced by microwave plasma chemical vapor deposition (MPCVD) from CH4:H2:N2 gas mixtures. The films were irradiated in air with 20 ns pulses of an ArF excimer laser (λ =193 nm). It was found that low laser pulse intensity (~ 0.05 J/cm2), well below film surface graphitization (~ 0.3 J/cm2) and nanoablation (~ 0.08 J/cm2) thresholds, induces changes of the film properties. The effect requires multiple pulsed irradiation and results in a decrease of the film electrical conductivity, which is accompanied by optical bleaching of the diamond film absorption.