Quantitative measurements of laser-generated acoustic waveforms

Dewhurst, R.J.; Hutchins, David A.; Palmer, S.B.; Scruby, C. B.

doi:10.1063/1.331270

Cited by 211 publications

(106 citation statements)

References 14 publications

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“…Only small differences are seen, which is explained by the small relative elastic and thermal impedances of water vs. Al. This result supports the supposition that large positive displacements observed with water layers [13] are caused by evaporation at the interface.…”

Section: 5supporting

confidence: 81%

“…One-dimensional models will not suffice: important features of the generated waveforms or.r.nr only when three-dimensional aspects are considered. Scruby et al [12,13] obtained considerable insight from a model invoking equivalent forces to represent a point thermal (surface) source, and Rose [1][2][3][4] has extended that understanding and given it a more rigorous foundation with an Analytical development based on a point temperature (surface) sm1rce. Experimental measurements (see reviews by Hutchins [1] and Hutchins and Tam [3]) are in good agreement, except for the small, positive "precursor" (menti_oned above), the source·of which has not been certain.…”

mentioning

confidence: 99%

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A New Method for Calculation of Laser-Generated Ultrasound Pulses

McDonald

1990

Review of Progress in Quantitative Nondestructive Evaluation

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Section: 5supporting

confidence: 81%

mentioning

confidence: 99%

A New Method for Calculation of Laser-Generated Ultrasound Pulses

McDonald

1990

Review of Progress in Quantitative Nondestructive Evaluation

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“…From a target surface modified with a very thin grease layer, the waveform displays typical characteristics [5], where monitoring laser power onto the target was 14 mW. This single shot waveform shows a sharp pulse corresponding to the longitudinal arrival of ultrasound (at"'" 3.7 p.s), virtually no shear signal (at"'" 7.4 p.s) and several side wall reflections (at"'" 9.6 p.s and beyond).…”

Section: Laser-ultrasonic Measurementsmentioning

confidence: 99%

An Actively-Stabilized Fiber-Optic Interferometer for Laser-Ultrasonic Flaw Detection

Pierce¹,

Corbett²,

Dewhurst³

1993

Review of Progress in Quantitative Nondestructive Evaluation

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“…The second type of generation mechanism can be created by removal of material from the surface of the sample. This can be by evaporation of a coating, applied to the surface prior to irradiation, or the ablation of the material itself [4]. In either case, the effect is to create a force due to material departing from the surface.…”

Section: Generation Mechanismsmentioning

confidence: 99%

Pulsed Lasers for Quantitative Ultrasonic NDE

Hutchins

1992

Review of Progress in Quantitative Nondestructive Evaluation

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There has been a lot of recent interest in the use of pulsed lasers for the generation of ultrasound in a range of media [1], due to advantages inherent in the generation process. These include the non-contact nature of the method, and the generation of a wide bandwidth over a small source area. The size and shape of the source can also be changed using suitable optics, as can the generation mechanism itself. Generation MechanismsIn general, there are three types of source characteristics that are available. The first uses optical power densities that are below that required for melting of the irradiated solid surface. This results in a transient heating of the substrate, leading to rapid thermal expansion and the radiation of elastic waves. This is the so-called thermoelastic effect and the resulting waveforms and characteristics have been studied widely [e.g. 2,3]. The second type of generation mechanism can be created by removal of material from the surface of the sample. This can be by evaporation of a coating, applied to the surface prior to irradiation, or the ablation of the material itself [4]. In either case, the effect is to create a force due to material departing from the surface. This force tends to be pulse-like, unlike the thermoelastic ca se where the incoming laser energy is integrated to become a step. Where an applied coating is absent, a mixture of these two mechanisms can lead to a range of waveforms and source characteristics, as the power density at the surface is varied. This is due primarily to the formation of a plasma elose to the surface of e.g. a metal, which prolongs ablation at higher power densities.A third mechanism has recently been identified, which uses the effect of plasma formation close to a surface, but not intimately connected to it as in the ca se of a metal above. This occurs when there is a relatively high optical reflectivity, such as is present with far infra-red laser radiation (e.g. a C02 laser). Here, the reflected energy and incidence pulse can combine to induce breakdown of the air close to the surface, but at some distance from it [5] . Types of DetectorsIt is evident from the above that a pulsed laser can be a flexible method for the NDE of many materials. However, for it to be a truly useful method, it needs to be combined with adeteetion system that is itself non-contact and whieh has a wide bandwidth. The most popular recent choice for detection has been interferometry. This is also an optieally-based approach, and leads to good detection sensitivity at a wide range of surfaces. The types of interferometers available have been reviewed by Monchalin [6], and there are now several devices available commercially. Recent advances in both heterodyne and Fabry-Perot designs now give good detection sensitivity, and with a pulsed laser source can lead to an NDE system that is capable of inspecting industrial materials [7]. Interferometry has severallimitations -it tends to be expensive, and requires a certain reflectivity at the deteetion surface. Despite these li...

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Quantitative measurements of laser-generated acoustic waveforms

Cited by 211 publications

References 14 publications

A New Method for Calculation of Laser-Generated Ultrasound Pulses

A New Method for Calculation of Laser-Generated Ultrasound Pulses

An Actively-Stabilized Fiber-Optic Interferometer for Laser-Ultrasonic Flaw Detection

Pulsed Lasers for Quantitative Ultrasonic NDE

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