A novel method for diameter estimation of small opaque objects using Fraunhofer diffraction

Khushi Vyas; Kameswara Rao Lolla

doi:10.1117/12.869591

2 September 2010 A novel method for diameter estimation of small opaque objects using Fraunhofer diffraction

Khushi Vyas, Kameswara Rao Lolla

Proceedings Volume 7792, Reflection, Scattering, and Diffraction from Surfaces II; 779219 (2010) https://doi.org/10.1117/12.869591
Event: SPIE Optical Engineering + Applications, 2010, San Diego, California, United States

Abstract

A novel optical method is proposed and demonstrated, for real-time dimension estimation of thin opaque cylindrical objects. The methodology relies on free-space Fraunhofer diffraction principle. The central region, of such tailored diffraction pattern obtained under suitable choice of illumination conditions, comprises of a pair of 'equal intensity maxima', whose separation remains constant and independent of the diameter of the diffracting object. An analysis of 'the intensity distribution in this region' reveals the following. At a point symmetrically located between the said maxima, the light intensity varies characteristically with diameter of the diffracting object, exhibiting a relatively stronger intensity modulation under spherical wave illumination than under a plane wave illumination. The analysis reveals further, that the said intensity variation with diameter is controllable by the illumination conditions. Exploiting these 'hitherto unexplored' features, the present communication reports for the first time, a reliable method of estimating diameter of thin opaque cylindrical objects in real-time, with nanometer resolution from single point intensity measurement. Based on the proposed methodology, results of few simulation and experimental investigations carried-out on metallic wires with diameters spanning the range of 5 to 50μm, are presented. The results show that proposed method is well-suited for high resolution on-line monitoring of ultrathin wire diameters, extensively used in micro-mechanics and semiconductor industries, where the conventional diffraction-based methods fail to produce accurate results.

Citation Download Citation

Khushi Vyas and Kameswara Rao Lolla "A novel method for diameter estimation of small opaque objects using Fraunhofer diffraction", Proc. SPIE 7792, Reflection, Scattering, and Diffraction from Surfaces II, 779219 (2 September 2010); https://doi.org/10.1117/12.869591

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