Application Study of Optical Fiber F-P Sensing System for Non-contact Measurement of Surface Defects

Laser ultrasound has many advantages such as being non-contact, nondestructive, fast, accurate and low cost. Therefore it is usually used as an effective way to detect and characterize small surface or subsurface breaking cracks. In this paper, the length of Fabry-Perot cavity is obtained based on interference principle of light. An optical fiber F-P interferometer is designed. The contact less type laser ultrasound experimental devices of optical fiber F-P are established for detecting surface defects. The results show that when the locations of the excitation source and the sensor are settled, with the constant length and depth of the rectangle defect, the longer the length of the defect is, the larger the amplitude of the reflected wave is, With the constant length, depth and width of the defect, the amplitude of the reflected wave is the largest when the excitation source is perpendicular to defect, the amplitude lowers gradually with the decreasing of rake angle. Until the excitation source is parallel to the defect. the amplitude is the lowest.