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Bragg spectroscopy is now possible in fluids of light.

We propose a novel method to measure the dispersion relation in a fluid of light using Bragg spectroscopy.

This novel method allows us to measure also the static structure factor.

Measurement of the Static Structure Factor in a Paraxial Fluid of Light Using Bragg-like Spectroscopy

Phys. Rev. Lett. 127, 023401 (2021)

We implement Bragg-like spectroscopy in a paraxial fluid of light by imprinting analogues of short Bragg pulses on the photon fluid using wavefront shaping with a spatial light modulator. We report a measurement of the static structure factor, S(k), and we find a quantitative agreement with the prediction of the Feynman relation revealing indirectly the presence of pair-correlated particles in the fluid. Finally, we improve the resolution over previous methods and obtain the dispersion relation including a linear phononic regime for weakly interacting photons and low sound velocity.