  We investigate the multipartite entanglement between spatial and spectral
modes of an optical parametric oscillator pumped with a structured light field.
When the pump beam is prepared in a second-order transverse mode, we show that
the down-converted signal and idler fields are generated in a reconfigurable
quadripartite entangled state of first-order modes. Our investigation is based
both on separability criteria and a thorough analysis of the squeezing
properties. Additionally, we demonstrate that large-scale entangled states can
be produced and easily controlled by a pump field structured in both spatial
and spectral domains. Our results pave the way for versatile cluster state
engineering with structured light modes.
