Analysis of masking effect on laser light scattering from unidirectional and isotropic machined surfaces

 

Juan de Dios Ortiz–Alvarado and Jorge A. Huerta–Ruelas

 

Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada Instituto Politécnico Nacional Laboratorio de Metrología Óptica Cerro Blanco 141 Colinas del Cimatario C.P. 76090 Querétaro, Querétaro México.

 

Recibido: 19 de marzo de 2009.
Aceptado: 4 de mayo de 2010.

 

Abstract

An experimental study of masking effect on laser light scattering from machined surfaces is described. The results indicate that asperity distribution on rough surfaces is an implied factor on masking effect in addition to roughness and RMS slope. The masking effect was monitored on light scattering from isotropic and unidirectional rough surfaces. The masking effect characterized in isotropic rough surfaces agrees with the shadowing–masking function defined by B.G. Smith [IEEE Trans. Ant. and Prop. 15 668 (1967)]. We propose a new expression defined to describe masking effect on light scattering from unidirectional machined surfaces. This function was verified by comparing with experimental data. The results and the function proposed, are useful in implementing laser light scattering instruments for on–line monitoring of surface processes which produce unidirectional surface patterns (such as turning, milling, grinding, and some cases of extrusion, lithography and thin film growth), where geometrical setup requires large incidence angle.

Keywords: Laser light scattering; Surface roughness; Shadowing effect; Masking effect; Optical roughness meter.

 

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Acknowledgements

This work was supported by CONACYT under project SEP–2004–C01–47938. Authors acknowledge to Arturo Moreno Baez with his help to implement mechanical positioning system. Also, it is recognized a fruitful discussions with Ph.D. Gerardo Miramontes de León and Ph.D. Ivan Dominguez López.

 

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