NOISE-REDUCTION IN TWIN-PULSED ADDITION ELECTRONIC SPECKLE PATTERN INTERFEROMETRY FRINGE PATTERNS

Addition fringe patterns are obtained in real time with electronic speckle pattern interferometry (ESPI) when two pulses are fired within a single field of a CCD camera, i.e., within 1/50 s. The ability to use ESPI in this manner means that target deformation can be studied in very severe environments. A major drawback is that the addition fringes are intrinsically noisy and of very low contrast, impeding a full analysis of the deformation. Experimental results are presented for two methods of reducing noise in addition fringe patterns: subtraction of a reference frame and subtraction of addition fringe patterns. The subtraction procedure leads to high-contrast fringes, which can contain information of both target deformation and rigid body motion. An analytical representation of this behavior is presented.