A light scanning unit that does not deteriorate print quality and has a simple
structure and a low-priced multi-beam shape. The light scanning unit includes a
composite light source in which a plurality of light sources for emitting coherent
light having different wavelengths are arranged adjacent to one another and an
optical axis of each light source is arranged almost parallel to each other and
which emits light at a divergeing angle centering on each optical axis, and an
optical system comprising a collimator lens arranged on an approximately central
axis of an optical axis of each light source comprising the composite light source
and collimates the light beam emitted from the composite light source, a cylinder
lens for condensing the light beam emitted from the collimator lens, and a polygonal
rotating mirror for scanning the light beam condensed by the cylinder lens in a
main scanning direction on an exposed surface of an exposed object, and each light
source is arranged adjacent to each other on a substrate having a gaseous layer
between excitation light-emitting portions of each of the light sources.
