Laser beam optical system capable of compensating focal length changes thereof

摘要

A laser beam light source device which has Fresnel lens having grating of unequal spacing and facing a laser diode, and condenser lens made of resin. The focal length of the condenser lens is set at a value which nullifies changes in the focal length of the Fresnel lens induced by fluctuations in the oscillation wavelength of the laser diode accompanying temperature change, and changes in the focal length of the Fresnel lens accompanying temperature change. Further a laser beam scanning optical system for scanning on a scan line via a deflecting device and optical elements by a laser beam emitted from a laser light source based on image information. In the laser scanning optical system, a pair of anamorphic lenses are disposed anteriorly and posteriorly to the deflecting device to correct surface tilt of the deflecting device, one of the anamorphic lens being a Fresnel lens, another of the anamorphic lens being made of resin.