A novel technique is proposed to unambiguously determine the magnitude and orientation of linear dichroism. It relies on the use of a dual-frequency dual-polarization coherent source emitting two orthogonal circularly polarized modes at the output. The interaction of such beam with dichroic media is shown to give rise to a beatnote signal in the radiofrequency range. The amplitude and phase of such beatnote makes it possible to fully determine the magnitude and orientation angle of the diattenuation. We also report the application of this method to polarimetric imaging, with promising perspectives in biomedical imaging. Indeed, it provides a direct characterization of dichroic sample orientation, showing uniform estimated dichroism magnitude, whatever the orientation of the sample.