To perform optical excitation, optical ionization, optical dissociation, optical degradation, optical separation, optical synthesis, optical formation, optical analysis or the like by generating an optical pass for making laser beam back and forth between the mirrors by a polygon mirror system using several kinds or one kind of the laser beam and introducing atomic beam, molecular beam, liquid beam, solid beam, plasma beam, particle beam or the like to the optical pass.

The polygon mirror device constituted so as to construct the polygon mirror system by arranging and fixing a plurality of mirrors to face each other by two or to provide stepwise, to shift the optical pass of several kinds or one kind of the laser beam running back and forth between the mirrors every back and forth movement to strike the different mirror and to cause many numbers of interactions with the medium (atomic and molecular gases, liquid, solid, plasma, particle beam) on the optical pass is used for an image transfer optical system for laser beam or as a resonator and a method to cause the optical reaction (optical excitation, optical ionization, optical dissociation, optical degradation, optical separation, optical synthesis, optical formation, optical analysis) with plural laser beams by connecting the singular or plural numbers of the laser beams to the singular or plural numbers of the polygon mirrors is provided.