A specification calls for a modulator able to switch a 633 nm beam at 5.0 MHz

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Optics & Photonics · Polarisation and anisotropic media

What an Instrument Can See, Ch Modulating light: electro-optic, acousto-optic and magneto-optic devices

Problem

A specification calls for a modulator able to switch a 633 nm beam at 5.0 MHz. Two candidate devices are on the bench. ((a)) A lumped-electrode Pockels cell, modelled as a capacitor of

C = 15\,\mathrm{pF}

driven by a source of output resistance

R = 50\,\Omega

. Estimate its 3 dB bandwidth. ((b)) A TeO

_2

acousto-optic modulator with a beam diameter

D = 3.0\,\mathrm{mm}

and acoustic velocity

v_a = 4200\,\mathrm{m\,s^{-1}}

. Estimate its modulation bandwidth from the acoustic transit time across the beam. ((c)) State which device (if either) meets the 5.0 MHz specification, and explain in one sentence why the acousto-optic result cannot be improved by faster driving electronics alone.

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