Patent ID: 6556306
Filing Date: 2003-04-29
Classification: G01N

Abstract:
A non-contact method for determining in a free space the index of refraction (n2(&ohgr;) at a desired angular frequency (&ohgr;) of a sample including a thin, transmissive film having a thickness (d) and optionally disposed on a substrate, the method comprising:(a) generating (i) an input desired-frequency pulse having a first wavelength and a first duration, and (ii) a probe pulse having a second wavelength shorter than the first wavelength and a second duration shorter than the first duration; (b) directing the input pulse along a first path and the probe pulse along a second path; (c) moving the sample in and out of the first path, creating an output pulse which alternates between a transmitted signal (Efilm(&ohgr;)), created when the sample is in the first path, and a reference signal (Eref(&ohgr;)), created when the sample is outside the first path; (d) modulating the probe pulse by the output pulse; (e) detecting the modulated probe pulse with a photo detector; (f) calculating a differential signal (Ediff(&ohgr;)) for the thin film comprising a difference between the transmitted signal and the reference signal; (g) repeating steps (a)-(f) over a plurality of delay times between the input pulse and the probe pulse until a complete field waveform of the differential signal for the thin film is characterized; and (h) calculating the index of refraction as a function of a ratio between the differential signal for the thin film and the reference signal.