Resolution and contrast enhancement of correlated imaging in photon counting regime

We theoretically discuss the four-photon spatial correlation property under different detection schemes. Compared with the two- and three-photon spatial correlation of thermal light source, we found that the enhancement in the visibility and the contrast when the fourth-order spatial correlation function is measured with quadruple coincidence measurement in the single photon counting regime. The resolution, however, is not changed when we scan three of four detectors with identical speed and direction. But if we scan two of three detectors in opposite directions and same speed, simultaneously, other two in identical direction and speed of one detector is twice of that of the other, we can see that both the contrast and resolution are improved significantly. We also show that the conclusion can be applied to the Nthorder ghost imaging.