• Journal of the Korean Society for Precision Engineering
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• v.26 no.7
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• pp.65-72
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• 2009

Laser interferometry is widely used as a measuring system in many fields because of its high resolution and its ability to measure a broad area in real-time all at once. In conventional laser interferometry, for example out-of-plane ESPI (Electronic Speckle Pattern Interferometry), in plane ESPI, shearography and holography, it uses PZT or other components as a phase shift instrumentation to extract 3-D deformation data, vibration mode and others. However, in most cases PZT has some disadvantages, which include nonlinear errors and limited time of use. In the present study, a new type of laser interferometry using a laser diode is proposed. Using Laser Diode Sinusoidal Phase Modulating (LD-SPM) interferometry, the phase modulation can be directly modulated by controlling the laser diode injection current thereby eliminating the need for PZT and its components. This makes the interferometry more compact. This paper reports on a new approach to the LD (Laser Diode) Modulating interferometry that involves four-frame phase shift method. This study proposes a four-frame phase mapping algorithm, which was developed to have a guaranteed application, to stabilize the system in the field and to be a user-friendly GUI. In this paper, the theory for LD wavelength modulation and sinusoidal phase modulation of LD modulating interferometry is shown. Using modulating laser and research of measurement algorithm does comparison with existent ESPI measurement algorithm. Algorithm measures using GPIB communication through most LabVIEW 8.2. GPIB communication does alteration through PC. Transformation of measurement object measures through modulating laser algorithm that develops. Comparison of algorithm of modulating laser developed newly with existent PZT algorithm compares transformation price through 3-D. Comparison of 4-frame phase mapping, unwrapping, 3-D is then introduced.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.177-184
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• 2012

An optical defect detection method using ESPI(electronic speckle pattern interferometry) is proposed. ESPI is widely used as a non-contact measurement system which show deformation and phase map in real time. ESPI can be divided as the in-plane, out-of-plane and shearography by operation principle and target object and also divided with bulk type and optic fiber type by the optic configurations. This paper is focused on optic fiber type out-of-plane ESPI, which has the following advantages: (1) low cost; (2) reduction of the unreliable factors generated by separated optic components; (3) simplification of the optic configuration; (4) great reduction of volume; (5) flexibility, to be easily designed into different structures to adapt to inaccessible environments such as pipeline cavity and so on.