Effect of partially coherent pump on the spatial and spectral profiles of down-converted photons

We report a theoretical study of spatial and spectral profiles of twin photons generated with a pump beam having a partially spatially coherent nature. These profiles are simulated for both type-I and type-H spontaneous parametric down conversion in collinear and non-collinear configurations and found to be highly dependent on the choice of beam waist and transverse correlation length of the pump beam. It is found that by suitable selection of coherence length and size of the pump beam, the asymmetry in spatial geometry of down-converted photons and the spectral width can be modified. Owing to the partially spatially coherent nature, these biphoton beams might offer more robustness against losses compared to their fully coherent counterparts, and thus could yield a high success rate in free-space quantum communication and in quantum key distribution. (C) 2020 Optical Society of America