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## VI. BRAGG SCATTERING IN A TRAPPED ATOMIC GAS 

<img src='content_image/334823.jpg'>

For illustration, we now consider the response of a trapped Fermi gas at unitarity to two- photon Bragg scattering due to first and second sound. We consider an experimental setup similar to that used in [37], where a pair of laser beams are applied to the gas such that the region where they overlap is confined to the centre of the gas. As a first approximation to this configuration, we assume that the overlap region between the two beams is isotropic, with a Gaussian profile: 

<img src='content_image/334830.jpg'>

Here, σ is the width of the Bragg beams and q and ω are the wavevector and frequency difference between the two beams. 

For a Bragg pulse of short duration ( τ ≪ 2 π/ω$_{0}$ , where ω$_{0}$ is the trap frequency), the 

