The equivalent of Fourier Holography at the nano-range

The paper deals with holographic interferometry at the nanometric scale. The observed objects discussed in this paper are sodium chloride nano-crystals. The crystals are phase objects; the classical holographic methodology for phase objects is applied. To produce the images a conventional microscope is utilized. A 6 m spherical lens acts as a relay lens to collect the wavefronts that a CCD attached to the microscope records. The analysis of the formed images is performed by digital procedures that yield the dimensions of the observed crystals. The main difference between conventional lens holography of phase objects and the methodology presented in this paper is that the observations are made well beyond the limits of optical resolution. This is made possible by utilizing as a source of illumination evanescent wavefronts. The crystals are self illuminating objects producing pseudo-non-diffracting wavefronts. The wavefronts emerging from the crystals are the result of electromagnetic resonances of the interfaces of the crystals with a glass surface that supports them. The mean absolute error in the length measurements is of the order of 3 nm and the standard deviation ±3.7 nm. The measured lengths of the crystals agree very well with integral numbers of the sodium chloride elementary cell size.