Scanning apparatus

Scanning apparatus for providing a substantially straight line scan of a radiation spot with a selected shape and orientation comprising:

• a source of coherent radiation having a wavelength .lambda.;
• a radial hologon mounted for rotation about an axis and having at least one pattern of parallel grating lines with a pitch d;
• means for forming radiation from said source into a collimated beam having an oblong cross-sectional shape and for directing said beam onto the hologon at a predetermined incident angle and with the long axis of the oblong cross-sectional shape of the beam, where incident on the hologon, being radial of the axis of rotation of the hologon;
• a target station for receiving the scanned beam;
• lens means between the hologon and the target station for focusing the beam to a spot at the target station;
• and
• prismatic means between the hologon and the lens means for so modifying the cross-sectional shape of the beam that the spot at the target station has the selected shape and orientation;
• the wavelength of the radiation and the grating factor (n.lambda.)/d (wherein n is the grating order number) of the hologon being selected to produce a bow in the scanned beam between the hologon and the prismatic means approximately equal and opposite to the bowing tendency imposed by the prismatic means on the scanned beam whereby the scan line at the imaging station is substantially straight.