A laser scanner at must offer at least resolvable spots and must be able to jump to a…

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Polarisation and anisotropic media · Polarisation and anisotropic media

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

Problem

A laser scanner at

\lambda_0 = 633\ \mathrm{nm}

must offer at least

N = 200

resolvable spots and must be able to jump to a new spot within

\tau = 5.0\ \mu\mathrm{s}

. It is built from a TeO

_2

cell driven by a longitudinal acoustic wave, with

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

and

n = 2.26

. The transducer can cover a drive band no wider than half its centre frequency. ((a)) Find the widest optical beam the access time allows, and the drive bandwidth the spot count then needs. ((b)) Find the lowest centre frequency the transducer allows, and the band of drive frequencies it spans. ((c)) Decide where in that band the cell comes closest to leaving the Bragg regime, and find the shortest interaction length that keeps

Q_{\mathrm{KC}} \ge 10

across the whole band. ((d)) Find the full scan angle outside the cell.

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