Apparatus and method for nano-identification a sample by measuring, with the use of evanescent waves, optical spectra of near-field interaction between the sample and optical nanoantenna oscillating at nano-distance above the sample and discriminating background backscattered radiation not sensitive to such near-field interaction. Discrimination may be effectuated by optical data acquisition at periodically repeated moments of nanoantenna oscillation without knowledge of distance separating nanoantenna and sample. Measurement includes chemical identification of sample on nano-scale, during which absolute value of phase corresponding to near-field radiation representing said interaction is measured directly, without offset. Calibration of apparatus and measurement is provided by performing, prior to sample measurement, a reference measurement of reference sample having known index of refraction. Nano-identification is realized with sub-50 nm resolution and, optionally, in the mid-infrared portion of the spectrum.