Patent ID: 8342028

Claim:
A photoacoustic measurement apparatus that irradiates a subject with a light beam, from a same side as that of an acoustic wave detector, and that measures photoacoustic waves, the apparatus comprising: an acoustic wave detector; a diffraction grating member provided in front of a detection surface of said acoustic wave detector; a light source that generates a light beam; and an optical system that guides the light beam from said light source towards said diffraction grating member, wherein said diffraction grating member is configured such that the light beam led to said diffraction grating member is outputted by said diffraction grating member towards a subject surface that opposes said detection surface of said acoustic wave detector, wherein the shape of said detection surface is rectangular or circular, and wherein said diffraction grating member is configured such that an incidence angle θ of the light beam outputted by said diffraction grating member with respect to the subject satisfies tan θ<L/2d, where L denotes a length of a short side or diameter of said detection surface, and d denotes a distance between said detection surface and a surface of contact with the subject.