Chemical nano-identification of a sample using normalized near-field spectroscopy

摘要

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.

主权项

1. A method for optical characterization of a sample (SUT) using evanescent waves, the method comprising:
detecting, with an optical detector, an optical signal interferometrically formed by
(i) first electromagnetic radiation backscattered by a nanoantenna in response to being incident electromagnetic radiation, said nanoantenna being controllably movable above a surface of the SUT, and(ii) second electromagnetic radiation representing a portion of said incident electromagnetic radiation, a phase-delay equal to a difference between a phase of the second electromagnetic radiation and a phase of the first electromagnetic radiation being variable; to form an optical data output; processing said optical data output in time domain to extract a first portion of said optical data output that represents electromagnetic field caused by near-field interaction between the nanoantenna and the surface of the SUT during a motion of the nanoantenna above the SUT, wherein said motion includes a recurring motion; and negating a contribution of said background electromagnetic radiation by irradiating the nanoantenna with light from a continuous-wave (CW) laser source, and detecting said optical signal only at the moments corresponding to a chosen phase of the recurring motion.