We investigate second harmonic generation (SHG) response of mesoscale silver (Ag) particles. The flower-like Ag mesoparticles and Ag micro-hemispheres on an indium tin oxide coated glass substrate were prepared by a simple electrochemical deposition method. We find that the mesoscale Ag particles show a strong SHG response associated with their geometries. The dependence of the SHG on the excitation wavelength reveals that the multi-resonant response occurring at the emission wavelengths plays an important role in SHG enhancement.

We show that the image quality of ghost imaging (GI) can be controlled by the use of shaped incoherent sources. The formula for the point-spread function in the GI system has been derived and is determined by the Fourier transform of the source intensity distribution. Compared with the widely used Gaussian Schell-model source, we find that using a cosine-Gaussian Schell-model source can lead to the degradation of GI quality, while the quality of GI can be increased with a cosh-Gaussian Schell-model source. Even under atmospheric turbulence, the image resolution of GI still can be improved by means of the cosh-Gaussian Schell-model source.

We propose a high-quality imaging method based on correspondence imaging (CI) using a sorting and compressive sensing (CS) technique. Unlike the traditional CI, the positive and negative (PN) subsets are created by a sorting method, and the image of an object is then recovered from the PN subsets using a CS technique. We compare the performance of the proposed method with different ghost imaging (GI) algorithms using the data from a single-detector computational GI system. The results demonstrate that our method enjoys excellent imaging and anti-interference capabilities, and can further reduce the measurement numbers compared with the direct use of CS in GI.

Imaging through atmospheric turbulence is a topic with a long history and grand challenges still exist in the remote sensing and astro observation fields. In this letter, we try to propose a simple scheme to improve the resolution of imaging through turbulence based on the computational ghost imaging (CGI) and computational ghost diffraction (CGD) setup via the laser beam shaping techniques. A unified theory of CGI and CGD through turbulence with the multi-Gaussian shaped incoherent source is developed, and numerical examples are given to see clearly the effects of the system parameters to CGI and CGD. Our results show that the atmospheric effect to the CGI and CGD system is closely related to the propagation distance between the source and the object. In addition, by properly increasing the beam order of the multi-Gaussian source, we can improve the resolution of CGI and CGD through turbulence relative to the commonly used Gaussian source. Therefore our results may find applications in remote sensing and astro observation.

Ghost imaging (GI) through a turbulent atmosphere with a new kind of Lorentz-shaped incoherent source is investigated. It is well known that the diffraction effect of a Lorentz beam is more robust to propagation distance than a Gaussian beam of the same beam size, which may be helpful for long-distance imaging through turbulence or scattering media. Here, an incoherent Lorentz source is first applied in a GI system to realize long-distance imaging through atmospheric turbulence. Based on the extended Huygens–Fresnel principle, an imaging formula for GI through turbulence with an incoherent Lorentz source is developed theoretically. The effects of the propagation distance and turbulent strength on the imaging quality are also studied numerically in detail. Compared with the widely used Gaussian sources, we find that the resolution of the GI system can be significantly improved by using an incoherent Lorentz source, especially under long-distance imaging conditions. Our work may thus have found a new way to improve the quality of GI through turbulence by using an incoherent Lorentz source, which can promote real applications of GI in the long-distance imaging field, such as remote sensing and astronomical observation.

Computational ghost imaging (CGI) is an indirect single-pixel imaging method that can retrieve an image of an object in a hostile environment by using a correlation of intensity fluctuations. Based on the theory of ghost imaging (GI) and using the spatial power spectrum of the refractive index of ocean water, we develop a unified imaging formula for the CGI and computational ghost diffraction (CGD) operating through oceanic turbulence, and numerically analyse how the image quality can be affected by oceanic turbulence including the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the rate of dissipation of mean-square temperature, and the relative strength of temperature salinity fluctuations, as well as the propagation distance. To quantitatively evaluate the quality of the retrieved images, the relative mean square error is employed in the CGI system. Our results show that the quality of the CGI scheme operating through oceanic turbulence is closely related to the propagation distance. When the propagation distance is fixed to be relatively small, we can effectively obtain a sharp image in the case of strong turbulence, and the turbulence influence can be neglected. Meanwhile the turbulence effects become more serious in the CGI system with increasing propagation distance. Besides, we find the CGI system is more robust against oceanic turbulence than the CGD system.

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Computational ghost diffraction (CGD) with a higher-order cosh-Gaussian modulated incoherent source is investigated theoretically. The corresponding numerical simulations are given to see clearly the effects of the parameters of the higher-order cosh-Gaussian source on the imaging quality. Our results show that the resolution of the CGD patterns can be significantly improved by properly varying the source parameters. In addition, we numerically study the effect of the propagation distances in the CGD system and explore the CGD applicability in coherent diffraction imaging. These results may be helpful for implementation of high-resolution x-ray diffraction.