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Near-field thermal radiation (NFTR) between two graphene-covered Si grating (G/Si grating) heterostructures consisting of multilayered G/Si grating cells is investigated, in comparison with that between single-G/Si-grating-cell structures. The calculations are based on the scattering theory utilizing rigorous coupled-wave analysis (RCWA). It is found that strong magnetic polaritons (MPs) can be induced in the single G/Si grating cell, and coupling of multiple MPs can be observed in multilayered G/Si grating heterostructures, which leads to a broader band of high photon-tunnelling probabilities in the phase space. As a result, when the thickness of each grating layer is fixed, the heat flux of the 4-G/Si grating heterostructures, with chemical potential μ = 0.1 eV and grating period Lx = 80 nm, is 1.65- and 9.12-fold larger than those of the 1-G/Si grating and only Si grating structures at d = 100 nm, respectively. When the total thickness of the entire G/Si grating heterostructure is fixed, the 1-G/Si grating model performs better than 2- or 4-G/Si grating models because higher loss inherited from additional graphene sheets would reduce the momenta of the near-unity energy transmission coefficient in the k-space.

Gyrotron devices are based on the principle of the relativistic electron cyclotron maser and capable of generating high-power coherent radiation in the millimeter-THz wave range, which are important in imaging, communication, biomedicine. However, traditional particle-in-cell software, simulating the beam-wave interaction of terahertz gyrotron devices, is of huge resource consumption due to massive particles and grid-size dependency of wavelength. Specialized theories need to be developed. In this paper, frequency-domain and time-domain nonlinear theories are introduced. Based on macro-particle assumption and 1-D analytic approximation, the resource consumption is dramatically reduced. The results of two theories coincide with each other. The accuracy of simulation result is demonstrated by comparison with particle-in-cell software. The investigation presented in this paper provides efficient and accurate method to analyze the terahertz gyrotron devices.

The interaction between unmodified CaCO3 nanoparticles and sodium dodecyl sulphate (SDS) in aqueous solution and the subsequent emulsification of the mixed dispersions are studied by means of zeta potential measurements, adsorption and emulsion characterization. Using toluene or octane as oil phase, hydrophilic CaCO3 nanoparticles stabilize only temporarily oil-in-water, O/W, emulsions. Upon the addition of trace amounts of SDS in the aqueous phase, the stability of the emulsions is greatly improved. Further increasing the SDS concentration results in a double phase inversion, O/W(1) to water-in-oil, W/O to O/W(2). It is suggested that the adsorption of SDS molecules on particle surfaces rendering them hydrophobic induces the first inversion. When the adsorption of SDS reaches a maximum, the surface of the particles are re-converted to hydrophilic due to a surfactant bilayer, and the equilibrium concentration of SDS in the continuous phase is high enough to stabilize a water continuous emulsion, promoting the second phase inversion. The O/W(2) emulsions however, are in general unstable, due to flocculation and sedimentation of the particles.