Nondestructive Testing (NDT) based on laser technology has witnessed incremental acceptance in the NDT industry since the early 1990’s with shearography and holography interferometry as the most widely recognized techniques based on this technology. Over the past decade, integration of lasers with ultrasonic testing has seen commercial acceptance in a number of different applications. Laser profilometry is another technique that has experienced growing adoption as a tool for surface mapping and when coupled with advanced software capabilities, this technique can be used for external surface corrosion assessment. These laser-based NDT techniques are the ones that have gained visibility in the industry with a niche market developing for laser visual inspection. Integration of lasers with cameras to offer a faster, more accurate technique for visual inspection capable of providing an image of the surface under test has created an important niche in the visual inspection market. However, considering the conservative nature of end users of NDT and the slow rate of change of technology in the NDT industry, realistically laser NDT, depending upon the technique, still has 5-10 years to go before it is widely accepted.
Although shearography and holography are spoken of in the same breath by many experts, there are subtle differences between the two techniques with holography in use for NDT applications earlier than shearography. Shearography gives the first derivative of the out of plane displacement, whereas holography measures absolute out of plane displacement of an object in response to an applied load.