Patent ID: 8767029

Claim:
A light source device comprising: a surface emitting laser; a coupling optical system that couples a light beam output from the surface emitting laser; and an aperture member having an aperture that regulates the light beam from the coupling optical system, the aperture being formed in such a size that a relationship of |(Pap 1 −Pap 2 )/Pap 2 |<|(P 1 −P 2 )/P 2 | is satisfied, where P 2 is a light intensity of the light beam entering the aperture member at a time t 2 when 2 microseconds have passed since current was applied to the surface emitting laser, P 1 is a light intensity of the light beam entering the aperture member at a time t 1 when 40 nanoseconds have passed since a light intensity of the light beam entering the aperture member reached 0.1 times the light intensity P 2 at the time t 2 , Pap 2 is a light intensity of the light beam output from the aperture member at the time t 2 , and Pap 1 is a light intensity of the light beam output from the aperture member at a time t 1 ″ when 40 nanoseconds have passed since a light intensity of the light beam output from the aperture member reached 0.1 times the light intensity Pap 2 at the time t 2 .