Publisher's Synopsis
Laser-based ultrasonics (LBU) is a technique that uses laser sources to generate and detect high-frequency ultrasound. Generation is accomplished by illuminating a sample with a short-pulse laser. The laser energy absorbed by the sample causes localized heating, with accompanying thermal expansion. Absorption of the incident pulse energy and the associated temperature gradients induces a rapidly changing strain field. Increased use of advanced materials and more stringent requirements for process and quality control are creating new needs for nondestructive inspection techniques. Ultrasonics is a widely used technique for defect detection in various materials and is being developed, and even in some cases actually applied for microstructural characterization. However, ultrasonics in its present state of implementation in industry suffers several limitations. Probing materials at elevated temperature is made difficult by fluid coupling problems. Inspecting specimens of complex shapes requires sophisticated robotic manipulators to properly orient the transducer. Furthermore, since the technique relies on a piezoelectric resonator to generate and receive ultrasound, it does not have the adequate bandwidth or sensitivity for some applications. Laser-ultrasonics which is based on lasers to generate and detect ultrasound could possibly eliminate these limitations. In this technique, generation of ultrasound originates from the absorption of light at the surface of the material, which creates a transient heat source, which in turn produces the thermoelastic stress at the origin of ultrasound. At higher laser power density a thin surface layer is vaporized which, by the recoil effect produces the normal stress at the origin of ultrasound. The characteristics of ultrasonic sources produced by lasers have been the object of intensive studies which have been reviewed. Concerning the detection aspect, the various techniques have also been reviewed recently and the most appropriate for industrial inspection appear to be based on velocity or time-delay interferometry. Laser Ultrasonics: Techniques and Applications delivers the wide-ranging applications in all fields involving both lasers and ultrasonics. The book reviews acousto-optics, various acousto-optic devices, and noninterferometric optical methods of measuring ultrasonic displacements. Conventional ultrasonic techniques have long been recognized for their usefulness in the nondestructive testing of materials and structures. These techniques, based on launching ultrasonic or high-frequency acoustic waves into a material using a coupled transducer, enable the probing of certain material properties. By inducing surface or bulk waves into a material, several material properties, such as thickness, layer structure, and elastic moduli, can be measured. Laser-based ultrasonics (LBU) is a technique that uses laser sources to generate and detect high-frequency ultrasound. Generation is accomplished by illuminating a sample with a short-pulse laser. The laser energy absorbed by the sample causes localized heating, with accompanying thermal expansion. Absorption of the incident pulse energy and the associated temperature gradients induces a rapidly changing strain field. Increased use of advanced materials and more stringent requirements for process and quality control are creating new needs for nondestructive inspection techniques. Ultrasonics is a widely used technique for defect detection in various materials and is being developed, and even in some cases actually applied for microstructural characterization. However, ultrasonics in its present state of implementation in industry suffers several limitations. Probing materials at elevated temperature is made difficult by fluid coupling problems. Inspecting specimens of complex shapes requires sophisticated robotic manipulators to properly orient the transducer. Furthermore, since the technique relies on a piezoelectric resonator to generate and receive ultrasound, it does not have the adequate bandwidth or sensitivity for some applications. Laser-ultrasonics which is based on lasers to generate and detect ultrasound could possibly eliminate these limitations. In this technique, generation of ultrasound originates from the absorption of light at the surface of the material, which creates a transient heat source, which in turn produces the thermoelastic stress at the origin of ultrasound. At higher laser power density a thin surface layer is vaporized which, by the recoil effect produces the normal stress at the origin of ultrasound. The characteristics of ultrasonic sources produced by lasers have been the object of intensive studies which have been reviewed. Concerning the detection aspect, the various techniques have also been reviewed recently and the most appropriate for industrial inspection appear to be based on velocity or time-delay interferometry. Laser Ultrasonics: Techniques and Applications delivers the wide-ranging applications in all fields involving both lasers and ultrasonics. The book reviews acousto-optics, various acousto-optic devices, and noninterferometric optical methods of measuring ultrasonic displacements. Conventional ultrasonic techniques have long been recognized for their usefulness in the nondestructive testing of materials and structures. These techniques, based on launching ultrasonic or high-frequency acoustic waves into a material using a coupled transducer, enable the probing of certain material properties. By inducing surface or bulk waves into a material, several material properties, such as thickness, layer structure, and elastic moduli, can be measured.