Sinusoidal wavelength-scanning interferometric reflectometry

We propose interferometric reflectometry in which a sinusoidal wavelength-s canning tunable laser diode is used to detect positions and profiles of mul tiple reflecting surfaces. An objective signal extracted from an interferen ce signal contains modulation amplitude Z and phase a, which are related to the positions and profiles, respectively, of multiple reflecting surfaces. By using values of the objective signal at special times, we can produce a n image intensity that shows where the reflecting surfaces exist. To obtain exact values of Z or values of a, we estimated the objective signal by usi ng a conjugate gradient method. Experimental results show that a resolution of two-optical-path difference (OPD) in the image intensity is similar to 60 mu m, and the final OPD precisions are 2 and 8 mu m for two and three re flecting surfaces, respectively, for a wavelength-scanning width of 7 nm. P rofiles of the front and rear surfaces of a silica glass plate with a thick ness of 20 mu m have been measured with a precision of similar to 10 nm. (C ) 2000 Optical Society of America OCIS codes: 120.3180, 110.4500, 120.6650.