Vortices estimation of speckle activity

H. RABAL; G. H. SENDRA; R. ARIZAGA; M. TRIVI

Sidney, Australia

Congreso; 21st Congress of the International Commission for Optics (ICO); 2008

International Comission for Optics

<!-- /* Font Definitions */ @font-face {font-family:Mangal; panose-1:0 0 4 0 0 0 0 0 0 0; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:32771 0 0 0 1 0;} @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-fareast-font-family:Calibri; mso-bidi-font-family:Mangal; mso-fareast-language:EN-US;} span.spelle {mso-style-name:spelle; mso-style-unhide:no;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt; mso-ascii-font-family:Calibri; mso-fareast-font-family:Calibri; mso-hansi-font-family:Calibri; mso-bidi-font-family:Mangal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Optical singularities (vortices), it is points in a speckle pattern where intensity is zero and consequently phase is not defined, have been shown to be useful tools for optical metrology of rigid movements achieving nanometre precision. When the sample is active, vortices move randomly and eventually vanish and/or are created. In this work, vortices are obtained in the Laguerre Gauss filtered images of a simulated displacing diffuser under pure boiling conditions. By employing a numerical model of active speckle simulation we show that the mean value of the displacement of the vortices is proportional to the diffuser speed in the limit of very low speeds. Homologous vortices are identified by using minimum Poincaré distance in a spherical surface of vortex core features and Euclidean distance is used as displacement measurement. As speeds are increased, ambiguity in the assignment of the correspondence increases, wrong assignments then increase and the measurement is not valid any more. This kind of measurement would be useful for the estimation of very low activities, such as those occurring in corrosion and efflorescence, which is difficult to be done with other dynamic speckle algorithms. Experimental results are also shown.