The authors demonstrate a rapid and convenient method for the determination of writing and erasing laser powers in phase-change media based on scanning surface potential microscopy using a conductive tip. Commercially available digital versatile disks that are rewritable with initialization process are measured in experiments. The results of measurement show that when the disk is rotating at 3.5 m/s linear velocity, the adequate writing and erasing of laser power are 10-15 and 4-8 mW, respectively. The critical laser power for crystallization conversion is 8 mW. The method used for this research can be satisfyingly applied to the development of new phase-change recording materials. (c) 2006 American Vacuum Society.