The Jeffree cell was an early acousto-optic modulator

Acousto-optic modulator

An acousto-optic modulator , also called a Bragg cell, uses the acousto-optic effect to diffract and shift the frequency of light using sound waves . They are used in lasers for Q-switching, telecommunications for signal modulation, and in spectroscopy for frequency control. A piezoelectric...

, best known for its use in the Scophony

Scophony

Scophony was a sophisticated mechanical television system developed in Britain by Scophony Limited, which used mirrors mounted on high-speed rotating drums to project an image upon a screen....

 system of mechanical television

Mechanical television

Mechanical television was a broadcast television system that used mechanical or electromechanical devices to capture and display video images. However, the images themselves were usually transmitted electronically and via radio waves...

. It was invented by J.H. Jeffree in 1934, and was a major improvement over the Kerr cell modulators used up to that time.

Using ultrasonic sound

Ultrasound

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...

 waves travelling perpendicular to the light, the modulator created areas of varying refractive index leading to advancement and retardation of portions of the light wavefront. This led to constructive and destructive interference among the light waves, modulating their intensity.

External links

• Scophony system at Early Television website