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Reflection and transmission (refraction) of a homogeneous plane wave at the planar boundary of two dielectric media is a well known phenomenon commonly treated in nearly all standard textbooks. Here the analysis of reflection and refraction of evanescent plane waves on the planar boundary between various combinations of lossy, gainy and lossless media is performed. It is shown that by the appropriate choice of the profile of evanescence various effects can take place.

We present a quasinormal-mode (QNM) theory for coupled loss and gain resonators working in the vicinity of an exceptional point. Assuming linear media, which can be fully quantified using the complex pole properties of the QNMs, we show how the QNMs yield a quantitatively accurate model to a full classical dipole spontaneous-emission response in Maxwell’s equations at a variety of spatial positions and frequencies (under linear response). We also develop an intuitive QNM coupled-mode theory, which can be used to accurately model such systems using only the QNMs of the bare resonators, where the hybrid QNMs of the complete system are automatically obtained. Near a lossy exceptional point, whose general properties are broadened and corrected through use of QNM theory, we analytically show how the QNMs yield a Lorentzian-like and a Lorentzian-squared-like response for the spontaneous-emission line shape consistent with other works. However, using rigorous analytical and numerical solutions for microdisk resonators, we demonstrate that the general line shapes are far richer than what has been previously predicted. Indeed, the classical picture of spontaneous emission can take on a wide range of positive and negative Purcell factors from the hybrid modes of the coupled loss-gain system. The negative Purcell factors are unphysical and signal a clear breakdown of the classical dipole picture of spontaneous emission in such media, though the concept of a negative local density of states is correct. This finding has enabled a quantum fix to the decay of a two-level-system dipole emitter in amplifying and lossy media [Franke et al., Phys. Rev. Lett. 127, 013602 (2021)], and we further show and discuss the impact of this fix using the QNMs of the microdisk resonators. We also show the rich spectral features of the Green’s function propagators, which can be used to model various physical observables, such as photon detection.

In this paper, the potential of a broadband metasurface for ground penetrating radar (GPR) signal enhancement is investigated by simulation and experiments. Simulation results show that the reflection at the air-MUT interface can be reduced from 35% to 5% over a broad frequency range (relative bandwidth up to 44%) when the broadband metasurface is in place. Measured reflectance is consistent with the simulation results. Meanwhile, the electric field strength measurement results demonstrate that the transmitted electromagnetic signals can be amplified when the reflection is reduced over the same frequency range. GPR experiments verified that clear hyperbolic signals emerged for commonly undetectable pipes when the high-frequency signals are enhanced. The proposed broadband metasurface can be an effective solution for the detection of nonmetallic inclusions in high-lossy media.

Waves entering a spatially uniform lossy medium typically undergo exponential intensity decay, arising from either the energy loss of the Beer–Lambert–Bouguer transmission law or the evanescent penetration during reflection. Recently, exceptional point singularities in non-Hermitian systems have been linked to unconventional wave propagation. Here, we theoretically propose and experimentally demonstrate exponential decay free wave propagation in a purely lossy medium. We observe up to 400-wave deep polynomial wave propagation accompanied by a uniformly distributed energy loss across a nanostructured photonic slab waveguide with exceptional points. We use coupled-mode theory and fully vectorial electromagnetic simulations to predict deep wave penetration manifesting spatially constant radiation losses through the entire structured waveguide region regardless of its length. The uncovered exponential decay free wave phenomenon is universal and holds true across all domains supporting physical waves, finding immediate applications for generating large, uniform and surface-normal free-space plane waves directly from dispersion-engineered photonic chip surfaces.Exceptional points in nanostructured lossy photonic waveguides lead to uniformly distributed losses and linear amplitude decay.

In this work, the propagation characteristics of tripolar breather trial solution in nonlocal nonlinear media with loss are studied theoretically. The approximate equations of parameters of the tripolar breather are obtained analytically by the variational method. The analytical solution was verified by numerical simulation. Tripolar loss soliton and tripolar loss breather can be formed under suitable incident conditions. By analogy with Newton’s laws of motion in classical mechanics, we regard the evolution of the triple breather as a particle with a mass equal to 1. By studying the evolution law of the equivalent force and the equivalent potential energy, the in-depth physical reasons for the periodic evolution of the tripolar breather are analyzed.

JPEG images are widely used in multimedia transmission, such as on social media platforms, owing to their efficiency for reducing storage and transmission requirements. However, because such images may contain sensitive information, encryption is essential to ensure data privacy. Traditional image encryption schemes face challenges when applied to JPEG images, as maintaining compatibility with the JPEG structure and managing the effects of lossy compression can distort encrypted data. Existing JPEG-compatible encryption methods, such as Encryption-then-Compression (EtC) and Compression-then-Encryption (CtE), typically employ a single encryption stage, either before or after compression, and often involve trade-offs between security, storage efficiency, and visual quality. In this work, an Encryption–Compression–Encryption algorithm is presented that preserves full JPEG compatibility while combining the advantages of both EtC and CtE schemes. In the proposed method, pixel-block encryption is first applied prior to JPEG compression, followed by selective coefficient encryption after compression, in which the quantized DC coefficient differences are permuted. Experimental results indicate that the second encryption stage enhances the entropy achieved in the first stage, with both stages complementing each other in terms of resistance to attacks. The addition of this second layer does not significantly impact storage efficiency or the visual quality of the decompressed image; however, it introduces a moderate increase in computational time due to the two-stage encryption process.

The subgridding finite-difference time-domain (FDTD) method has a great attraction in ground penetrating radar (GPR) modeling. The challenge is that the interpolation of the field unknowns at the multiscale grid interfaces will aggravate the asymmetry of the numerical system which results in its instability. In this paper, an explicit unconditionally stable technique for a lossy object is introduced into the subgridding FDTD method. It removes the eigenmodes of the coefficient matrix which make the algorithm unstable. Therefore, the proposed approach not only maintains the advantages of simple implementation of the traditional FDTD method but also adopts a relatively large time step in both coarse and fine grid, which breaks through the restriction of the Courant-Friedrichs-Lewy (CFL) stability condition. The proposed method is applied in simulating the transverse magnetic (TM) wave backscattering of the two-dimensional buried objects in lossy media. Its accuracy and efficiency are examined by comparison with conventional FDTD and subgridding FDTD approaches.

With the wide use of social media platforms, the critical matter is to reduce the image size while maintaining the image quality to achieve faster transfer speeds over the networks and save space on storage devices. The compression techniques are categorized into lossless and lossy. Lossless techniques produced high-quality compressed images with no loss of any part of the images, but it has low performance compared to the lossy technique with high distortion rates. This paper studies the effects of applying the Minimum Decreasing Technique (MDT) over a set of lossy compression techniques and evaluates the impact on the image quality and size. This was achieved by applying specific steps that decrease the minimum pixel values from the pixel values inside the image. We implemented the MDT technique first before using the lossy ones on several images wildly used in the image processing field. The results were obtained based on quality standard metrics (MSE, MAE, PSNR, and CR). The MDT technique managed to keep the image quality as is without increasing or decreasing in the metrics when used with the lossy techniques, whether alone or hybrid; it also managed to reduce the compression ratio due to the MDT mechanism, which depends on the other arrays included with the compressed image. Moreover, the results showed the highest compression ratio obtained by the proposed technique with 2–8% impartments compared to the other single or hybrid methods.

There exist multiple different even non-equivalent expressions describing characteristics of electromagnetic wave energy flow and momentum in media, which makes the issue confusing. For simplicity (without loss of generality), we shall consider a case where a harmonic homogeneous plane wave (HHPW) travels in a homogeneous isotropic linear medium (HILM); thus, both time-dependent Poynting’s vector S⃑(t) and time-dependent momentum density G⃑(t) are rigorously derived from continuity equations. Then, referring to recent studies of stored and dissipated energies of electromagnetic waves in lossy media, time-averaged Poynting’s vector and time-averaged momentum density are obtained according to the time dependence of the terms arising in the expressions of S⃑(t) and G⃑(t), respectively. On this basis, a new way is proposed to determine the direction relation between and of HHPWs in an HILM, and it is demonstrated that, in an HILM, the propagation direction of is always consistent with that of , which may be applied to explain why the predicted reversal of electromagnetic wave momentum in a left-handed material has not been observed up to now. This work may be helpful to further discuss, and even eliminate, the confusion arising in related issues, and deepen the understanding of the energy flow and momentum of electromagnetic waves in media.

The persistently unsolved Abraham–Minkowski controversy (A-MC) is usually associated with division of the total energy–momentum density tensor into electromagnetic and material components. In this work, characteristics of energy and momentum of electromagnetic waves in free space, lossless and lossy media are, respectively, addressed non-relativistically based on conservation or continuity equations. Combining progress of relativistic studies on A-MC and related topics, we demonstrate that, comparing with the treatment of dividing total momentum into electromagnetic and material components, to self-consistently describe properties of both electromagnetic energy and momentum, it is more favorable to take the electromagnetic wave arising in media as a natural whole, i.e., both energy and momentum are no longer to be divided into electromagnetic and material components. This work may be useful to properly describe energy and momentum of electromagnetic waves in media, find reasonable solution of A-MC, and further develop theory of electrodynamics of moving media.