Santos, Elkin A.Elkin A.SantosSetzpfandt, FrankFrankSetzpfandtSaravi, SinaSinaSaravi2026-02-242026-02-242023https://publica.fraunhofer.de/handle/publica/50800510.1109/CLEO/EUROPE-EQEC57999.2023.102325492-s2.0-85175710620The process of spontaneous parametric down-conversion (SPDC) in χ⁽²⁾-materials, in which a pump (P) photon of wavelength λP can split into a pair of entangled signal (S) and idler (I) photons of lower energy, is an instrumental tool in optical quantum technologies. Recently, there has been a growing interest in pair generation in sub-wavelength-thin nonlinear crystals [1,2], especially because they are not restricted by the phase-matching condition and exhibit SPDC in a very wide spectral and angular range. This also motivates their use in quantum imaging applications, for pushing the resolution of such schemes to the limit [3,4]. Despite its seemingly simple appearance, there has not yet been a comprehensive theoretical analysis of photon-pair generation in a thin unstructured nonlinear slab. Specifically, a proper theory should embed the Fabry-Pérot type of interferences that the signal and idler photons experience in such a nonlinear etalon during SPDC.enfalseconference paper