  A bipartite multiphoton entangled state is created through stimulated
parametric down-conversion of strong laser pulses in a nonlinear crystal. It is
shown how detectors that do not resolve photon number can be used to analyze
such multiphoton states. Entanglement of up to 12 photons is detected using
both the positivity of the partially transposed density matrix and a newly
derived criteria. Furthermore, evidence is provided for entanglement of up to
100 photons. The multi-particle quantum state is such that even in the case of
an overall photon collection and detection efficiency as low as a few percent,
entanglement remains and can be detected.
