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We perform a theoretical study on the two-photon scattering effect of a single Mie scatterer, and investigate its dependence on the rotation angle of the scatterer, and the wavelength and polarization of incident light. Different regions of the two-photon correlation map are recognized by investigating two parameters, i.e., the visibility of two-photon superposition that represents the path information of different two-photon paths, and the balance factor of the double-side single-photon scattering amplitude that indicates the possibility of the single-photon scattering process. It is shown that the two-photon scattering pattern is a result of two-photon interference from the incoherent to fully coherent regime, together with a contribution from a single-photon-like correlation. In the coherent two-photon interference region, it is found that the transition from destructive to constructive interference emerges by rotating the scatterer, as well as by changing the polarization of incident light. These results demonstrate the rich features of the two-photon scattering effect for a single Mie scatterer, and open new possibilities to explore nano scatterers for controlling two-photon interference, and their applications in communications, sensing, and imaging.

Single-pixel imaging (SPI) is a novel lens-free imaging method quite different from the conventional spatially resolved imaging, yet it suffers the Rayleigh resolution limit imposed by the illumination aperture. Here we show that the Rayleigh resolution limit in SPI can be overcome by employing optical fluctuation. With Nth-order autocorrelation of the signal measured by the bucket detector in SPI, the imaging resolution can surpass the Rayleigh resolution limit by a factor of N. This result is important for optical microscopy based on SPI.

While a three-dimensional (3D) scattering medium is from the outset opaque, such a medium sustains intriguing transport channels with near-unity transmission that are pursued for fundamental reasons and for applications in solid-state lighting, random lasers, solar cells, and biomedical optics. Here, we study the 3D spatially resolved distribution of the energy density of light in a 3D scattering medium upon the excitation of highly transmitting channels. The coupling into these channels is excited by spatially shaping the incident optical wavefronts to a focus on the back surface. To probe the local energy density, we excite isolated fluorescent nanospheres distributed inside the medium. From the spatial fluorescent intensity pattern we obtain the position of each nanosphere, while the total fluorescent intensity gauges the energy density. Our 3D spatially resolved measurements reveal that the differential fluorescent enhancement changes with depth, up to 26× at the back surface of the medium, and the enhancement reveals a strong peak versus transverse position. We successfully interpret our results with a newly developed 3D model without adjustable parameters that considers the time-reversed diffusion starting from a point source at the back surface.

By generalizing the phase structure of the random-phase grating we recently designed [Opt. Express21, 14056 (2013)OPEXFF1094-408710.1364/OE.21.014056], we show that non-HBT type (synchronous position) two-photon grating interference can be obtained, which physically relies on groups of multiple indistinguishable two-photon paths modulated by the spatial distributions of phase modes. By properly selecting the random-phase structures, synchronous position subwavelength interference can be obtained, the period of which, in the two-photon interference domain, is decreased by a factor N (=3,4,5,6,…), depending on the slit number and random-phase structure, and the visibility of N-fold subwavelength interference fringes could be improved by increasing the slit number of the grating. The results show that modulation on two-photon paths via spatial arrangements of the phase modes offers the possibility to actively control the optical high-order coherence in the same optical scheme.