In order to investigate the most important parameters influencing the breaking characteristic of a vacuum circuit breaker (VCB). the behavior of copper (Cu) particles emitted from electrodes designed as an imitation of a vacuum valve of the VCB was observed. The temporal-spatial intensity distributions due to Cu particles in an excited state or a neutral state were measured using tile laser induced fluorescence (LIF) technique and a charge coupled device camera attached with a special filter. The diffusion velocity, of a Cu atom was also investigated by evaluating a Doppler shift of the LIF signal. The results showed that most Cu particles were emitted from the anode and were in an excited state or an ionized state during an arc discharge. Also, Cu particles were distributed between electrodes even after the discharge chocked, and its diffusion velocity in the direction of the cathode from the anode was about 2.6 km/s. (C) 2003 American Vacuum Society.