Lu Zhang, Dongxu Zhou, Yiping Lu, Hongzhi Zhang, Guoquan Zhang, "Super-bunched focusing with chirped random-phase gratings," Photonics Res. 8, 503 (2020)

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- Photonics Research
- Vol. 8, Issue 4, 503 (2020)

Fig. 1. (a) Schematic diagram of the designed slit-width-chirped random-phase grating. a n (n = 1 , 2 , … , N ) is the width of the n th slit, and N is the total slit number of the grating; ϕ ( t ) is a random phase changing with time among [ 0 , 2 π ) , 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; L 1 , L 2 , L 3 , lenses; A 1 , A 2 , 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 L 3 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 { a n } 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 { b k } 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.

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