Fig. 1. (a) Schematic diagram of the designed slit-width-chirped random-phase grating. an (n=1,2,…,N) is the width of the nth slit, and N is the total slit number of the grating; ϕ(t) is a random phase changing with time among [0,2π), and d is the fixed period of the grating. (b) Schematic configuration for studying the coherence property of the light field transmitting through the chirped random-phase grating in the Fraunhofer zone, where L represents a lens for collecting the scattering light from the chirped random-phase gratings and CCD is the charge-coupled device camera for recording the intensity distribution on the focal plane of lens L. (c) Schematic diagram of indistinguishable two-photon paths.

Fig. 2. Schematic diagram of the experimental setup. λ/2, half-wave plate; L1, L2, L3, lenses; A1, A2, irises; BE, beam expander; P, polarizer; BS, 50∶50 beam splitter; CRPG, chirped random-phase grating; CCD, charge-coupled device camera. The straight arrows in the optical path indicate the propagating and scattering light. The upper-right inset shows the detailed structure of the chirped random-phase grating, which is composed of an N-slit black–white transmitting amplitude mask and an SLM, and they are placed as close as possible. The lower-left inset shows the object placed on the focal plane of L3 in the ghost imaging experiments.

Fig. 3. Experimental results for the super-bunched focusing effect with (a) slit-width-chirped random-phase gratings and (b) period-chirped random-phase gratings. The grating period in (a) was fixed at d=400  μm, and the chirped slit width {an} values are listed in Appendix B.1. In (b), the slit width was set to be a=100  μm, and the chirped grating grid lines {bk} are listed in Appendix B.2. The black solid curves, the blue dash-dotted curves, and the red dotted curves depict the results for N=4, 8, and 16, respectively.

Fig. 4. Experimental results for the super-bunched focusing effect through chirped random-phase gratings with N=50. (a) Slit-width-chirped random-phase grating with a fixed period d=200  μm, (b) period-chirped random-phase grating with a fixed slit width a=30  μm. The corresponding structure parameters can be found in Appendices B.3 and B.4, respectively.

Fig. 5. Normalized ghost image profiles with super-bunched focusing light fields for (a) the slit-width-chirped random-phase gratings and (b) the period-chirped random-phase gratings. The shaded parts represent the opaque areas of the double-slit mask. The blue dashed curves, the green dotted curves, the red dash-dotted curves, and the pink dash-dot-dotted curves depict the results with N=4, 8, 16, and 50, respectively. For comparison, the black solid curves show the case of a pseudo-thermal light field generated through a phase-only SLM.