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The scanning laser source (SLS) technique has been proposed recently as an effective way to investigate small surface-breaking defects. By monitoring the changes in amplitude and frequency of the ultrasound generated as a laser source scans over a defect, the SLS technique has provided enhanced signal-to-noise performance compared to the traditional pitch–catch or pulse–echo ultrasonic methods. In the previous work, the laser ultrasound source was in the near-field of a scatterer and an optical or piezoelectric detector was used to measure the ultrasound in the far-field. We now propose an extension of the SLS approach to map defects in microdevices by bringing both the generator and the receiver to the near-field scattering region of the defects. To facilitate near-field ultrasound measurement, silicon microcantilever probes are fabricated using microfabrication techniques and their acoustical characteristics are investigated. The fundamental frequency of the microcantilever is measured and compared with analytically calculated fundamental frequency. The performance of the fabricated microcantilevers as resonant ultrasound detectors is investigated. Bulk and surface acoustic waves are generated with specific narrowband frequencies and the surface ultrasonic displacements are detected using the microcantilever probe. Next, broadband ultrasound is generated by a laser source and the resulting surface acoustic displacements are monitored using the microcantilever probe in the near-field of the ultrasound source. Finally, both the laser-generated ultrasonic source and the microcantilever probe are used to monitor near-field scattering by a surface-breaking defect.

This paper describes an optical technique for shape measurement that works satisfactorily in relatively severe noisy conditions by using additive - subtractive phase-modulated electronic speckle pattern interferometry (AS-ESPI). Through repetitively altering the illumination angle of one interfering beam at a frequency much higher than the video frame rate, and by simultaneously locking the beam tilting via laser strobing, random noises that normally are of much lower frequency than that of the repetitive tilting can be removed by frame averaging of the AS-ESPI correlation fringe patterns. A procedure of phase shifting that is synchronized with the repetitive tilting is utilized to perform data reduction. Quantitative experimental results obtained under rather noisy conditions are presented to show the validity of the principle.

A dual-purpose camera for both shearography and electronic speckle-pattern interferometry (ESPI) based on the concept of additive - subtractive phase-modulated speckle interferometry has been designed and tested. The compact camera can be operated either in ESPI mode or in shearography mode by simply adjusting a moving mirror in the camera head. This camera has been designed as an optical part of an automatic inspection system for disbond detection in aircraft structures. The primary advantage is the possibility of obtaining information both about an object's displacement and about its gradient using a single low-cost device suitable for field applications.

In the present investigation we study the effects of film-deposition time duration on thermal diffusivity (α) of hydrogenated amorphous carbon (a-C:H) thin-films grown in a radio-frequency (RF) plasma enhanced chemical vapor deposition system. A set of films was deposited at 50 W RF power for 40, 60, 80, and 100 min. Film characteristics were determined from the optical transmission spectroscopy, Fourier Transform Infrared spectroscopy, and Raman spectroscopy. Thermal diffusivity of a-C:H films was evaluated using the optical pump-and-probe technique on the aluminum-coated samples. Results show a trend of increase in α as the deposition time increases due to the microstructural changes associated with longer exposure to ion bombardment effects on the growth surface of the films.

Thermal properties of hydrogenated amorphous carbon (a-C:H) thin-films are measured using an ultrafast optical pump-probe technique. The a-C:H samples were grown in a home-built direct-current (DC) plasma enhanced chemical vapor deposition (PECVD) system with varying hydrogen (H2) diluents to methane (CH4) flow-rate ratios. Thermal diffusivities of samples are extracted by comparing thermoreflectance measurements with numerical calculations so that thermal conductivities (k) can be determined. Although the dependence of thermal property on H2 dilution was not significant, our films show lower k (0.10–0.15 W/mK ± 20%) compared to the results of previous studies.

A group delay measurement technique is proposed using modally selective Lamb wave transducers for the detection and sizing of delaminations in unidirectional and cross-ply composites. Unlike amplitude or energy based Lamb wave methods, this method is insensitive to transducer coupling. Specifically, modally selective array transducers are used to generate the lowest antisymmetric A0 Lamb mode in a zone with minimal dispersion. The change in the modal group velocity is used as a damage indicator while the accumulated time delay of the traveling ultrasonic wavepacket is used for size estimation of the delaminations. The results are repeatable and consistent, suggesting time delay as a reliable damage parameter for quantitative monitoring of delaminations and impact damage in composites.