“Seeing” into Opaque Materials with Light and Sound
By David M. Pepper, Todd W. Murray
Lasers generate and detect ultrasonic waves that can image the interiors of solid objects.
This Article From Issue
November-December 2023
Volume 111, Number 6
Page 352
People have always been fascinated by things that are hidden from view, and by what might be found inside opaque objects. We see objects because some of the light that strikes them is reflected and eventually enters our eyes. However, not all of the light is reflected from the surface; part of it is absorbed. Is there anything useful that can be done with this absorbed light to see within the object? The answer lies in a serendipitous observation made more than 140 years ago by Alexander Graham Bell when he heard sounds produced by light falling on an opaque object.
QUICK TAKE
- Opaque objects that are illuminated do not reflect all of the light that hits their surfaces; some of the light is absorbed and can create vibrations within the material.
- Lasers can both create and detect ultrasonic wave signals, which are modified by defects or other structures inside the opaque material and produce a measurable signal.
- Peering inside opaque materials without touching or damaging them is useful in manufacturing inspection, infrastructure monitoring, landmine detection, and medical imaging.
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