High-power UV light is being studied as a source for photolithography. The KrF laser is a candidate, but its spectrum spreads wide, which causes chromatic aberration in the optical system. The second harmonics light of the copper-vapor laser (CVL) has a wavelength similar to that of the KrF laser. Since the spectral width of the CVL is much narrower than that of the excimer laser, the use of the CVL avoids chromatic aberration. Furthermore, the high repetition rate of the CVL operation evens out the output energy fluctuation. Thus, if high conversion efficiency is achieved, this is a good source for photolithography.