Spatial extra-bunching effect in classical light

Thermal light by nature exhibits the well-known photon bunching effect with the zero-delay second-order correlation coefficient ${g}^{(2)}$ ideally equal to 2. The Photon extra-bunching effect, as a special class of the superbunching effect (${g}^{(2)}>2$), describes the enhanced photon correlation (${g}^{(2)}=3$) through the interference of bright twin beams produced in the spontaneous parametric down-conversion. In this work, we report that this effect can exist in classical beams and that ${g}^{(2)}$ can approach 4 in some extended extreme models. We experimentally demonstrate the nontrivial extra-bunching correlation ($\ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}$ gain) in pairwise-generated holographic thermal light beams with a Dove prism-embedded balanced Mach-Zehnder interferometer. The interaction of such a pair of conjugated thermal light beams can generate a pair of uncorrelated superthermal light beams, enabling ghost imaging and Young's intensity interference with enhanced visibility. The quantum-inspired interference-induced spatial extra-bunching effect provides novel insights into inducing superbunching correlation in classical light and holds the potential for application in the coherent two-photon Lidar system to enhance sensitivity.