. . . "Moreover, the substrate to be treated is a wafer here, but it can be adopted to all kinds of substrates, such as reticles and substrates for liquid crystals. [0131] A light with the band narrowed to a 470 nm wavelength (half width: 5 nm) by a lamp house 1601 capable of dispersing by a narrow-band pass filter is introduced via an optical fiber 1602 to two monitor heads 1603, 1614 placed separated f" .