The interferometer version of the enhanced scattering diagnostic (IES) is theoretically analysed and applied to diagnose lower hybrid test waves, revealing its ability in principle to provide the wavenumber spectrum of coherent small-scale waves or fluctuations in a magnetized plasma. Both the spectrum as well as the spatial structure of density perturbations obtained from these measurements are in reasonable agreement with the results of radio frequency (RF) probe measurements if one takes into account the different sensitivities of the two methods with respect to the wavenumber.