Making sound with light: Laser Generated Ultrasound by Dr Theodosia Stratoudaki, University of Strathclyde
Ultrasound has given us the power to “see” inside optically opaque materials and has had an undeniable impact in applications ranging from medical imaging, to sonars, to non-destructive testing. The question is: can we make ultrasound using light? The answer is “yes” and there are certain advantages for doing so: Light can sense remotely in extreme environments, such as the extreme heat of manufacturing processes, nuclear environments or space; optical beams can be delivered through optical fibres which can reach places of restricted access, such as the inside of an aero-engine or the human body. The development of advanced materials and miniaturised designs, is continuously pushing ultrasonic performance limits to extremes, including demands for large bandwidth and high ultrasonic frequencies and this is where optics are best suited.
The “photo-acoustic” effect or the way to turn light into sound, has been known as early as the 19th century but it has been waiting for the invention of the laser in the ‘60s to take off in the way of applications. The material irradiated by the laser is the ultrasonic source and plays the role of the “transducer”, as known in conventional ultrasonics. The mechanism for generating ultrasound by means of light can be thermoelastic or ablative. In addition, the ultrasonic source can be manipulated, either by spatial or temporal modification or both, in order to focus or steer or otherwise enhance ultrasonic generation. The aim of this tutorial is to give an insight into laser generation of ultrasound, its challenges, future directions and various applications.
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