A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites

Abstract

Laser ultrasonic (LU) inspection represents an attractive, non-contact method to evaluate composite materials. Current non-contact systems, however, have relatively low sensitivity compared to contact piezoelectric detection. They are also difficult to adjust, very expensive, and strongly influenced by environmental noise. Here, we demonstrate that most of these drawbacks can be eliminated by combining a new generation of compact, inexpensive fiber lasers with new developments in fiber telecommunication optics and an optimally designed balanced probe scheme. In particular, a new type of a balanced fiber-optic Sagnac interferometer is presented as part of an all-optical LU pump-probe system for non-destructive testing and evaluation of aircraft composites. The performance of the LU system is demonstrated on a composite sample with known defects. Wide-band ultrasound probe signals are generated directly at the sample surface with a pulsed fiber laser delivering nanosecond laser pulses at a repetition rate up to 76 kHz rate with a pulse energy of 0.6 mJ. A balanced fiber-optic Sagnac interferometer is employed to detect pressure signals at the same point on the composite surface. A-and B-scans obtained with the Sagnac interferometer are compared to those made with a contact wide-band polyvinylidene fluoride transducer. V C 2014 AIP Publishing LLC. [http://dx

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“…The use of a laser transmitter and receiver and the interaction of the incident ultrasonic wave with sub-surface and surface defects have been widely investigated for many different applications, as demonstrated in [11][12][13][14][15][16].…”

Photoacoustic Imaging in Gastroenterology: Advances and Needs

“…Conventional piezoelectric transducers limit the potential axial resolution of broadband PA signals. Note that all-optical detectors of PA signal are wideband and have significant advantage in these terms [22,23].…”

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“…Disadvantages include its low pulse repetition frequency (PRF), the high cost of pump lasers, and some issues with stability and the low sensitivity of optical reception. These limitations, however, have been recently overcome with a new kHz-rate fiber-optic pump-probe system [46] , [47] using a modified Sagnac interferometer as the detector [48] , [49] to achieve sensitivity rivaling the best contact US transducers.…”