  Quantum states of light with multiple spatial modes are fundamental for
quantum imaging and parallel quantum information processing. Thus, their
characterization, which can be achieved through measurements of the coherence
area, is an important area of research. We present a comparative study between
two different measurement techniques for the coherence area of bright entangled
twin beams of light generated with a four-wave mixing process in a hot rubidium
vapor cell. The first one provides a direct characterization of the size of the
coherence area and is based on correlation measurements between spatial
intensity fluctuations of the twin beams with an electron-multiplying
charge-coupled-device camera. The second one provides an indirect measure and
is based on a noise analysis of different spatial regions of the twin beams in
the time domain with a single photodiode. We show that the indirect technique,
which can be implemented with a significantly less complicated measurement
scheme, gives an estimate of the size of the coherence area consistent with the
direct measurement technique performed in the spatial domain.
