A double-pass acousto-optic frequency shifter sends the first-order diffracted beam…

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 double-pass acousto-optic frequency shifter sends the first-order diffracted beam through a lens and flat mirror, back through the same acousto-optic cell along a path that again satisfies the Bragg condition on the same travelling acoustic wave, and out. The cell is fused silica, driven at fa=200 MHzf_a = 200\,\mathrm{MHz} with acoustic velocity va=5960 m s−1v_a = 5960\,\mathrm{m\,s^{-1}}, and the light has vacuum wavelength λ0=1064 nm\lambda_0 = 1064\,\mathrm{nm}. ((a)) Find the full angle, measured outside the cell, between the undiffracted and the first-order beams after a single pass. ((b)) Find the total frequency shift of the light after the double pass. ((c)) The returning beam travels exactly opposite to the first-order beam. Using kd=ki+K\mathbf k_d=\mathbf k_i+\mathbf K, find the direction of the beam after its second diffraction, and state its angular deviation from the line of the input beam.

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