Two-color ghost imaging

Nondegenerate-wavelength (or two-color) ghost imaging using either thermal or quantum light sources is studied theoretically. We demonstrate that a high-quality ghost image can be obtained even when the wavelengths of light used in the object and reference arms are very different. The spatial resolution of the ghost image is found in general to depend on each of these wavelengths, although in many practical situations it depends primarily on the wavelength used to illuminate the object. The resolution of nondegenerate-wavelength thermal ghost imaging can be higher than that of its quantum counterpart despite the fact that the photons have the same degree of spatial correlation in the two cases.