Patent ID: 7286156

Claim:
A light source device for scanning-exposure comprising: a semiconductor laser having a substrate that is transparent to a wavelength of a laser beam emitted from an active layer; a condenser lens for converging said laser beam at least in a direction parallel to an active surface of said active layer; and a light flux limiting device for limiting light flux on an exit side of said condenser lens so as to eliminate extraneous light that is radiated from said substrate, wherein said light flux limiting device is located at a depth position Z on an optical axis of said condenser lens, said depth position Z satisfying conditions defined as follows: Z≧Z0, Z0<0 and Pp ⁡ ( Z0 ) = lim Z → ∞ ⁢ { Pp ⁡ ( Z ) } wherein Z is assumed to have a positive value on a forward side of said laser beam from a focal point of said laser beam through said condenser lens, Pp(Z) is a value obtained by dividing a width of said laser beam in said parallel direction to said active surface at said depth position Z by a width of said extraneous light in said parallel direction at said depth position Z.