The invention concerns an optical head for equipping the distal end of a flexible optical fiber bundle (2), designed to be urged into contact with an analyzing surface and comprising optical means (3) for focusing an excitation signal into a so-called excitation focal point located at a specific depth beneath the analyzing surface and for sampling a signal backscattered by the excitation focal point which is carried back by said fiber bundle. The invention is characterized in that it comprises an optics-holder tube (4) wherein are inserted on one side the distal end portion (1) of the fiber bundle (2) and on the other optical means, the latter including a plate (21) placed in contact with the end (14) of the fiber bundle whereof the index is close to that of the fiber core and a focusing optical block (3), an output window (30) being further provided adapted to provide index adaptation so as to eliminate parasitic reflection occurring on the analyzing surface.