Monitoring attenuation and the elastic properties of an apple with laser ultrasound

• A non-contacting all-optical method for acoustic monitoring of an apple is presented.
• Elastic wave velocities can be used to estimate an apple's elastic properties.
• Elastic wave attenuation and mode Q factor estimate an apple's anelastic properties.
• Apple ripeness decreases wave amplitude at a greater rate than wave velocity.

The firmness of an apple is a commonly used indicator of quality and maturity during sorting and cold storage. Its dependence on the elastic properties means that vibration resonance tests are favored over other – often destructive – tests. We present a novel non-destructive and non-contacting method using laser-generated and laser-detected elastic waves to infer the elastic modulus and Poisson's ratio of an apple from the velocity of surface and body waves. In addition, we analyze the attenuation of these waves. Although the elastic and anelastic properties all decay with age, attenuation is the most sensitive to changes in ripeness of the apple.