Diffraction of collinear correlated photon pairs by an ultrasonic wave within Raman–Nath and intermediate region

• Collinear correlated photon pairs diffraction by ultrasonic wave was investigated.
• Raman–Nath regime was investigated for collinear correlated photon pairs.
• Correlations between photons in diffraction orders varies with Raman–Nath parameter.
• A simple model of the interaction of photon pairs with ultrasonic wave was suggested.

The phenomenon of collinear correlated photon pairs diffraction by an ultrasonic wave is investigated within Raman–Nath and intermediate region. The numbers of single photons and photon pairs counts in discrete diffraction orders were measured as functions of the Raman–Nath parameter. Similarly, the number of coincidence photon counts in separate diffraction orders was also investigated. It was shown experimentally that the phenomenon of photon pairs diffraction by an ultrasonic wave happens at angles identical to those corresponding to single photons diffraction. It was also demonstrated that in case of Raman–Nath diffraction the number of photon pairs in a selected, nth, diffraction order varies with the Raman–Nath parameter changes as an nth order Bessel function of the first kind, raised to the fourth power. Whilst in the so-called intermediate diffraction zone, the number of diffracted photon pairs varies as squared intensity of a diffracted light beam consisting of single photons. Moreover, it was revealed that correlations between photons in selected diffraction orders change with the Raman–Nath parameter variation as products of relevant intensities of light in the considered diffraction orders. Finally, it should be emphasized that the presented formulae describing diffraction of collinear correlated proton pairs by an ultrasonic wave are in a very good agreement with corresponding experimental data, for both Raman–Nath and intermediate diffraction.