You can find the online document here.
Publication appeared in Physical Review A
A femtosecond-pulsed UV-laser beam passes twice through a β-barium borate (BBO) crystal, producing pairs of polarization-entangled photons. The photons are emitted in forward and backward directions and are recombined on polarizing beam splitters (PBSs). Walk-off effects are compensated using HWPs and half-thick BBOs. Additional HWPs set the entangled pairs to a selected Bell state. By postselecting fourfold coincidence events we obtain the desired cluster state or GHZ state. Polarization analysis is implemented with motorized tomographic optic components.