SiGnal Processing Techniques For Nondestructive Evaluation Using Laser Ultrasonics
Laser ultrasonics is a form of ultrasonic evaluation in which a pulsed laser generates an ultrasonic wave in a sample which interrogates a specific feature. When this wave returns to the surface a separate laser interferometer detects the small resulting displacement. This technique is strictly noncontact and is thus suitable for in-process inspection of parts at high temperature or moving at high speed. In many applications the acquired temporal signals have features which differ from those acquired using conventional transducers. In this paper we will describe these features and discuss techniques which have been used to process these signals.
Design and engineering of photorefractive materials for use in adaptive laser ultrasonic receivers
We describe the use of photorefractive material in adaptive interferometers for the detection of small surface displacements generated by ultrasonic waves. Recent results on devices based on two-wave mixing and photo-emf detection will be presented. We will discuss techniques for tailoring materials properties for improved device performance.
Laser shock processing with 20 MW laser pulses delivered by optical fibers
A large-core multi mode optical fiber is used to deliver 100 mJ, 5 ns laser pulses produced by a frequency-doubled Nd:YAG laser over a distance of several meters. No damage is observed neither inside the fiber nor at its surface. The transmitted pulses are focused to a diameter of 700 μ m onto a water-immersed type 304 stainless steel sample for laser shock processing. With a pulse density of 10000 pulses/cm 2 , a compressive residual surface stress is achieved. The affected depth is almost 900 μ m, the maximum compressive stress −700 MPa.