Kam Wai Clifford Chan

We compare the performance of high-order thermal ghost imaging with that of conventional (that is, lowest-order) thermal ghost imaging for different data processing methods. Particular attention is given to high-order thermal ghost imaging with background normalization and conventional ghost imaging with background subtraction. The contrast-to-noise ratio (CNR) of the ghost image is used as the figure of merit for the comparison. We find analytically that the CNR of the normalized high-order ghost image is inversely proportional to the square root of the number of transmitting pixels of the object. This scaling law is independent of the exponents used in calculating the high-order correlation and is the same as that of conventional ghost imaging with background subtraction. We find that no data processing procedure performs better than lowest-order ghost imaging with background subtraction. Our results are found to be able to explain the observations of a recent experiment [Chen et al., arXiv:0902.3713v3 [quant-ph]].

We show theoretically that high-order thermal ghost imaging has considerably higher visibility and contrast-to-noise ratio than conventional thermal ghost imaging, which utilizes the lowest-order intensity cross correlation of the object and the reference signal. We also deduce the optimal power order of the correlation that gives the best contrast-to-noise ratio.

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.

We show that high-order ghost imaging has higher visibility and contrast-to-noise ratio as compared to conventional thermal ghost imaging. We also obtain the optimal polynomial order that gives the best contrast-to-noise ratio.

We study a quantum ghost imaging system that uses different wavelengths to illuminate the object and the reference detector. We found that the resolution is limited by the wavelength of light illuminating the object.