Laser interference methods with focused probing beams for thickness measurements

Dmitry V. Lyakin; Vladimir P. Ryabukho; Mikhail I. Lobachev; Irina F. Minenkova; Sergei S. Ulyanov

doi:10.1117/12.518161

26 September 2003 Laser interference methods with focused probing beams for thickness measurements

Dmitry V. Lyakin, Vladimir P. Ryabukho, Mikhail I. Lobachev, Irina F. Minenkova, Sergei S. Ulyanov

Proceedings Volume 5134, Current Research on Holography and Interferometric Methods for Measurement of Object Properties: 2000-2002; (2003) https://doi.org/10.1117/12.518161
Event: Holography and Interferometric Methods for Measurement of Object Properties: 2000-2002, 2000, Unknown, United States

Abstract

Two laser interferometric methods with focused laser probing beam for thickness measurements of transparent films and layers are discussed. In both methods the exact focusing of probing beam on the objects surface permit to determine the parameters of random inhomogeneous objects, such as coatings on the rough surfaces. The first of the methods is a so-called focused oblique laser beam (FOLB) method. In this method at illumination by focused oblique laser beam of transparent layer with rough rear surface the reflected field performs superposition of beams with smooth and speckle-modulated wave fronts. The quasiregular interference pattern in reflected field is observed when the waist of focused laser beam overlap a rough rear surface of tested layer. Knowing the angular period of observed interference fringes and refractive index of layer medium one can determine the local geometrical thickness of a layer. The second method is based on the so-called Laser Wave Front Matching Interferometer (LWFMI) which is constructed under scheme of Michelson interferometer with focusing microobjectives in the interferometer branches (Linnik scheme) and wide integrating detector aperture in common exit branch. In the envelope of interference LWFMI signal as a function of object displacement relatively to a focal point of an interferometer focusing objective the peaks are observed when the probing beam is focused on the front and rear surfaces of a layer. The distance bewteen the interference signal peaks is proportional to the geometrical thickness of a layer and can be measured by the technique of interference fringe counting. As in the first method geometrical thickness can be obtained, if the refractive index of layer medium is known.

Citation Download Citation

Dmitry V. Lyakin, Vladimir P. Ryabukho, Mikhail I. Lobachev, Irina F. Minenkova, and Sergei S. Ulyanov "Laser interference methods with focused probing beams for thickness measurements", Proc. SPIE 5134, Current Research on Holography and Interferometric Methods for Measurement of Object Properties: 2000-2002, (26 September 2003); https://doi.org/10.1117/12.518161

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