NPL's Acoustics division uses the acousto-optic effect to characterise the propagation of sound within a variety of materials.

Light can be affected by acoustic waves as they vibrate through a material. This effect can be utilised and there are three NPL acoustics divisions (sound in air, underwater acoustics and ultrasound) which all use it as a tool to quickly characterise the propagation of sound. Applications in ultrasound include targeted treatment for cancerous tumours using High Intensity Focussed Ultrasound (HIFU).