https://www.selleckchem.com/products/g007-lk.html In an imaging system, resolution and signal-to-noise ratio (SNR) are two important indexes to characterize imaging quality. Ghost imaging is a novel imaging method whose imaging resolution and SNR are affected by the speckle size. In this paper, the relation between speckle size and resolution as well as that between speckle size and SNR in the GI system is analyzed in detail. It is shown that the critical resolution, resolvable minimum-separation between two adjacent objects, is approximately equal to the speckle size (speckle diameter). There exists an optimum SNR when the speckle size is larger than the object size. Based on our conclusion, we propose a scheme to enhance the critical resolution of the GI system by using a vortex beam, and the enhancement ability under different topological charges is clearly presented, which can be quantized by a simple formula.We study the coherent scattering process of photons in two waveguides chiral coupling to a Λ-type three-level system (3LS). The 3LS acts as a few-photon router that can direct photons with unity. By adjusting the classical field applied to the 3LS, the tunneling paths between two waveguides can be turned off and on, but two photons can not be routed simultaneously from one port of the incident waveguide to an arbitrarily selected port of the other waveguide. Moreover, driven field controls the number of the bi-photon bound states and the interference pattern of the bi-photon bound states.An analytical three-dimensional (3D) coupled-wave theory (CWT) for the finite-size photonic crystal slabs (PhCs) has been presented to depict the discretized modes at band-edges residing inside and outside the continuum. Specifically, we derive the CWT equations of slow-varying envelop function of dominant Bloch waves. By combining the trial solutions that are composed of a basis of bulk states with appropriate boundary conditions (B.C.), we analytically solve the equations