Contouring by electronic speckle pattern interferometry with quadruple-beam illumination

Abstract

We present a new arrangement for contouring by electronic speckle pattern interferometry with four illumination beams, thereby making it unnecessary to move anything during the measurement.Key words: Contouring, interferometry, speckle phenomena, metrology Optical contourin g techniques applie d o n a rough surfac e by mean s o f electroni c speckl e patter n interferometr y (ESPI) hav e bee n develope d fo r three-dimensiona l shap e analysis an d topograph y measurement.1-5 Correlatio n fringes ar e shown afte r th e subtractio n o r addition o f the video signal s fro m tw o speckl e patterns. On e ca n obtai n the contou r dat a fro m th e correlatio n fringe s b y usin g a phase-shifting metho d an d algorithm.6 Th e existing contouring methods by ESPI consist o f using two-wavelengt h illumination 1 or altering the object illumination beam 2,3 in a conventiona l ESP I syste m wit h a smoot h interferenc e reference bea m an d alterin g th e object 4 o r shiftin g th e illumination beams 5 in a dual-beam system. We presen t a n inexpensiv e ESP I arrangemen t wher e nothing i s move d t o obtai n contou r fringes . Onc e thi s system i s wel l adjusted , i t ca n be used simpl y an d practically, e.g., in a black box with a complete program packag e for fringe analysis. Th e schematic of such an arrangement is show n i n Fig . 1 . Th e collimate d lase r beam i s split b y the first bea m splitte r BSi , then combine d agai n with th e second prism beam splitter BS 2 with a small angle difference. Mirror M 5 play s th e rol e o f a directio n compensato r fo r forming correct contour planes.

A systematic approach to TV holography

“…The contouring surfaces are parallel to the observation direction and the contouring interval once again follows expression (3.41). The tilting of the illumination directions, which is common to all these techniques, can be implemented by use of tilting mirrors or translating lenses [107,108], by switching two sets of fixed illumination beams [109] or by use of tilting diffraction gratings [110]. Large objects have to be illuminated with diverging beams; in that case the tilting can be performed by translating their foci [101], but the effect of the curved wavefront must be corrected [111] for absolute contouring.…”