Method for correcting beam intensity upon scanning and recording a picture

A method for correcting the beam intensity upon scanning and recording a picture by means of a picture scanning and recording system which produces, on the basis of a picture signal, a halftone signal consisting of at least one parallel operation signal, causing at least one exposing laser beam, which has been modulated by at least one acousto-optic light modulator controlled by the halftone signal, to enter the input terminal of at least one optical fiber, tip portions of the output terminals of which optical fibers are aligned in a row where the system is equipped with more than one optical fiber, and projecting the thus-transmitted beam from the tip portion of the optical fiber on a recording drum, which method comprises:

• fixedly providing a half mirror between a lens, which is adapted to focus the thus-transmitted beam on the recording drum, and the tip portion of the optical fiber;
• focusing an image, which has been produced at the tip portion of the optical fiber, on at least one photo-electric sensor via the half mirror;
• and
• feeding an output signal of the photoelectric sensor, which output signal varies when the spectrum pattern on each output of the optical fiber varies as the output terminal of the optical fiber moves and the optical axis of the optical fiber thus changes, back to the acousto-optic light modulator so that the intensity of the exposing laser beam is corrected to the standard beam intensity required to expose a photosensitive material applied on the recording drum;
• the beam intensity of the output from each optical fiber being corrected to the standard beam intensity I.sub.30 by:
• determining the beam intensity I.sub.3 of the lens output, which beam intensity I.sub.3 is expressed by the following equation:
• I.sub.3 =I.sub.1 f(X).alpha.
• where
• I.sub.1 :
• the beam intensity of the laser beam input to the acousto-optic light modulator;
• I.sub.3 :
• the beam intensity of the laser beam output from the acousto-optic light modulator;
• f(X):
• the modulation characteristics of the acousto-optic light modulator;
• .alpha.:
• the extent of attenuation of the optical fiber;
• X:
• an input fed to a controller for each acousto-optic light modulator so as to change the output of the acousto-optic light modulator,
• as well as the central value .alpha..sub.0 of .alpha. and X.sub.0 when the beam intensity I.sub.3 of the output of the lens is equal to the standard beam intensity I.sub.30 required to expose the photosensitive material, namely, when I.sub.30 =I.sub.1 f(X.sub.0).alpha..sub.0 ;
• employing X.sub.0 as a standard datum X.sub.0 ;
• establishing a standard data table ##EQU5## feeding X.sub.0 to the controller for the acousto-optic modulator and measuring the beam intensity of the output of the acousto-optic light modulator upon scanning a surface of the recording drum on which surface the photosensitive material is not applied;
• obtaining, as X.sub.1, the value X when the product obtained by multiplying the beam intensity with the standard data table ##EQU6## is equal to I.sub.30, namely, when ##EQU7## and then feed X to the acousto-optic light modulator.