Coherent imaging of a pure phase object with classical incoherent light

By using the ghost imaging technique, we experimentally demonstrate the reconstruction of the diffraction
pattern of a pure phase object by using the classical correlation of incoherent thermal light split on a beam
splitter. The results once again underline that entanglement is not a necessary feature of ghost imaging. The
light we use is spatially highly incoherent with respect to the object (2 micron speckle size) and is produced by
a pseudo-thermal source relying on the principle of near-field scattering. We show that in these conditions no
information on the phase object can be retrieved by only measuring the light that passed through it, neither in
a direct measurement nor in a Hanbury Brown-Twiss (HBT) scheme. In general, we show a remarkable
complementarity between ghost imaging and the HBT scheme when dealing with a phase object