Abstract

Fourth-order coherence determines the visibility of interference fringes observed in two-photon correlation measurements. In some cases, one photon triggers the presence of its conjugate twin in the interferometer. Therefore, spatial or spectral filtering of the trigger photon may change the visibility of the interference fringes and the degree of fourth-order coherence as well. We show that, contrary to the intuition developed from series of previous experiments, it is possible to increase the fourth-order coherence by reducing the degree of filtering. We present a theoretical approach and experimental results demonstrating this effect and interpret it in terms of spatial mode parity selection.