In this study, the authors measured the density of Cu atoms in a magnetron sputtering plasma source employing an YBaCuO target by laser-induced fluorescence imaging spectroscopy. It was observed that, when pure Ar gas was used, the Cu density varied temporally after the initiation of. the discharge. The temporal variation was examined as a function of the gas pressure and the input rf power as well as the experimental sequence. When the Ar gas pressure was 300 mTorr, the Cu density decreased to 60% of the initial value after the transient period of 6 min at a rf power of 30 W, while at a rf power of 70 W, the transient period was 10 min and the Cu density at the steady state was 30% of the initial value. The transient period and the steady-state density showed hystereses, and the different transient periods and steady-state densities were observed at different experimental sequences. On the other hand, when the mixture of Ar and O-2 (0.7%) was used as the discharge gas, the Cu density was stationary at a value which was approximately 40%-60% of that observed in the pure Ar discharge at the steady state. The Cu atom density had the maximum at an 02 flow rate ratio of 7.4%. (c) 2006 American Vacuum Society.