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 (~1.4× 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.