Abstract: A laser beam scanning device including a plurality of laser beam sources for emitting laser beams having properties different from each other, respectively such that each of the laser beams is modulated by an image signal, a deflection member for simultaneously deflecting the laser beams emitted by the laser beam sources, a light detecting member for detecting one of the laser beams such that modulation of the laser beams emitted by the laser beam sources is started in response to a signal outputted from the light detecting member and an optical member which is disposed on an optical path from the deflection member to the light detecting member and optically selects only the one of the laser beams so as to irradiate the one of the laser beams onto the light detecting member.

Abstract: This invention discloses an improved catalyst for the polymerization or copolymerization of olefins, and a process for preparing polyolefins which comprises polymerizing or copolymerizing olefins using the said catalyst. According to the invention there is provided a process for preparing polyolefins by polymerizing or copolymerizing olefins using as a catalyst at least one compound selected from the group consisting of a titanium compound and a vanadium compound supported on a solid carrier, and an organometallic compound, said solid carrier comprising a product obtained by treatment with SO.sub.3 of at least one member selected from the group consisting of an oxide of Group II-IV metals of the Periodic Table and a double oxide of the said oxide and other oxide, which other oxide may be another oxide of Group II-IV metals of the Periodic Table or may be an oxide of other Group metals of the same Table.