  Spontaneous parametric downconversion is the primary source to generate
entangled photon pairs in quantum photonics laboratories. Depending on the
experimental design, the generated photon pairs can be correlated in the
frequency spectrum, polarisation, position-momentum, and spatial modes.
Exploring the spatial modes' correlation has hitherto been limited to the polar
coordinates' azimuthal angle, and a few attempts to study Walsh modes radial
states. Here, we study the full-mode correlation, on a Laguerre-Gauss basis,
between photon pairs generated in a type-I crystal. Furthermore, we explore the
effect of a structured pump beam possessing different spatial modes onto
bi-photon spatial correlation. Finally, we use the capability to project over
arbitrary spatial mode superpositions to perform the bi-photon state's full
quantum tomography in a 16-dimensional subspace.
