Entangled photon pairs—discrete light quanta that exhibit non-classical correlations—play a crucial role in quantum information science (for example, in demonstrations of quantum non-locality1,2,3,4,5,6,7, quantum teleportation8,9 and quantum cryptography10,11,12,31). At the macroscopic optical-field level non-classical correlations can also be important, as in the case of squeezed light13, entangled light beams14,15 and teleportation of continuous quantum variables16. Here we use stimulated parametric down-conversion to study entangled states of light that bridge the gap between discrete and macroscopic optical quantum correlations. We demonstrate experimentally the onset of laser-like action for entangled photons, through the creation and amplification of the spin-1/2 and spin-1 singlet states consisting of two and four photons, respectively. This entanglement structure holds great promise in quantum information science where there is a strong demand for entangled states of increasing complexity.