Fig. 1. Scheme of the NIQPR.

Two correlated beams labeled signal (s) and idler (i) are generated by the spontaneous parametric down conversion (SPDC) pumped by a CW laser @405 nm and propagate through an imaging system composed of two lenses (L₁ is the far field lens with focal length F = 1 cm and L₂ is the imaging lens with focal length of 3 cm) and a test object. An interference filter (IF) is used to select a bandwidth of 40 nm around the degenerate wavelength (@810 nm) and to block the pump. L₂ images the far field plane on the camera chip with a magnification factor of about 8. The object is placed near to the far field of the source, and only the probe beam interacts with it. Phase information can be retrieved^53,66 from intensity measurements taken at some out of focus (±dz) planes