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Abstract
Laser ultrasonics conventionally use direct absorption in the sample to generate ultrasound and monitor the sample to detect the ultrasound. However, in some circumstances there are significant advantages to using an optical transducer – a device to facilitate the conversion of optical energy into acoustic energy or to facilitate the modulation of light by an acoustic wave.
These devices are known as ‘cheap optical transducers’ (CHOTs). For some applications, they offer considerable advantages over conventional laser ultrasonics or conventional contact ultrasonics. In this paper, the design, operation and applications of CHOTs are discussed, and the concept is extended to the use of superCHOTs that can achieve amplitudes and sensitivities above the usual laser ultrasound limits, nano-scale devices capable of the generation and the detection of ultrasound with wavelengths smaller than that of visible light and devices capable of generating modes not normally accessible to laser ultrasound.
Acknowledgements
We would like to thank the Engineering and Physical Sciences Research Council (EPSRC), the Research Centre in Non-destructive Evaluation (RCNDE), the EU and Rolls-Royce plc.