A Bragg-type acousto-optic beam deflector is built in a crystalline material in which the acoustic velocity is 2500 m/s. The crystal has a refractive index n = 1.6. (a) What is the acoustic wavelength...

A Bragg-type acousto-optic beam deflector is built in a crystalline material

in which the acoustic velocity is 2500 m/s. The crystal has a refractive index

n = 1.6.

(a) What is the acoustic wavelength required to deflect a He-Ne laser beam

(λ0 = 6328 A) at a Bragg angle of 1 ˚ ◦)

(b) What is the corresponding acoustic frequency?

(c) Sketch an interdigitated metal-finger transducer such as could be

deposited on the surface of the crystal to launch a surface acoustic wave

with the wavelength calculated in (a). Show how the voltage would be

applied to the fingers and label the acoustic wavelength with an arrow

between the appropriate fingers.