| 摘要 |
PURPOSE:To compensate properly a scanning shift by continuously detecting the positional shift of a laser beam during the period of scanning and adjusting the carrier frequency of an optical modulator on the basis of the detected result. CONSTITUTION:The diffraction angle 2theta of a diffracted light B1 of laser light B from non-diffracted light B0 is expressed as 2theta lambda.f/v on the basis of the wavelength lambda of light, the ultrasonic wave speed (v) of an acoustic/optical medium and carrier frequency (f). When there is no surface inclination in a polyhedral mirror 5, laser light B1 scans the surface of dots 7a of a laser scanning position detector 7 at the time of frequency f=fa. When the irradiation of the laser light B1 upon dots 7alpha+i of the detector 7 is detected because of surface inclination, the carrier frequency is adjusted to f=fa+i so as to be compensated by the positional shift of the dots. Consequently, a regular scanning position can be scanned at a beam irradiation starting position 81 on a drum.
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