  In this letter, we demonstrate the experimental mapping of the longitudinal
magnetic and electric optical fields with a standard scanning microscope that
involves a high numerical aperture far-field objective. The imaging concept
relies upon the insertion of an azimuthal or a radial polarizer within the
detection path of the microscope which acts as an optical electromagnetic
filter aimed at transmitting selectively to the detector the signal from the
magnetic or electric longitudinal fields present in the detection volume,
respectively. The resulting system is thus versatile, non invasive, of high
resolution, and shows high detection efficiencies. Magnetic optical properties
of physical and biological micro and nano-structures may thus be revealed with
a far-field microscope.
