Fig. 1. Interferometric setup for the homodyne near-field measurements. Radiation propagating along the signal arm of the interferometer is focussed onto the cantilever, the backscattered light is directed onto the TeraFET detector. The reference arm with the movable mirror enhances the signal level on the detector if the mirror is positioned for constructive interference. Phase changes by the sample-under-test are identified by measurements at various mirror positions.