Unidirectional Photonic Reflector Using a Defective Atomic Lattice

Based on the broken spatial symmetry, we propose a novel scheme for engineering a unidirectional photonic reflector using a one-dimensional atomic lattice with defective cells that have been specifically designed to be vacant. By trapping three-level atoms and driving them into the regime of electromagnetically induced transparency, and through the skillful design of the number and position of vacant cells in the lattice, numerical simulations demonstrate that a broad and high unidirectional reflection region can be realized within EIT window. This proposed unidirectional reflector scheme provides a new platform for achieving optical nonreciprocity and has potential applications for designing optical circuits and devices of nonreciprocity at extremely low energy levels

The fermi arc and fermi pocket in cuprates in a short-range diagonal stripe phase

In this paper we studied the fermi arc and the fermi pocket in cuprates in a short-range diagonal stripe phase with wave vectors $(7\pi/8, 7\pi/8)$, which reproduce with a high accuracy the positions and sizes of the fermi arc and fermi pocket and the superstructure in cuprates observed by Meng et al\cite{Meng}. The low-energy spectral function indicates that the fermi pocket results from the main band and the shadow band at the fermi energy. Above the fermi energy the shadow band gradually departs away from the main band, leaving a fermi arc. Thus we conclude that the fermi arc and fermi pocket can be fully attributed to the stripe phase but has nothing to do with pairing. Incorporating a d-wave pairing potential in the stripe phase the spectral weight in the antinodal region is removed, leaving a clean fermi pocket in the nodal region.Comment: 5 pages, 6 figure

A Study on Improving the Efficacy of Nanoparticle-Based Photothermal Therapy: From Nanoscale to Micron Scale to Millimeter Scale

Photothermal therapy based on nanoparticles is a promising method for cancer treatment. However, there are still many limits in practical application. During photothermal therapy, improving therapeutic effect is contradictory to reducing overheating in healthy tissues. We should make the temperature distribution more uniform and reduce the damage of healthy tissue caused by overheating. In the present work, we develop a simple computational method to analyze the temperature distribution during photothermal therapy at three levels (nanoscale, micron scale, and millimeter scale), and investigate the effects of nanoparticle size, volume fraction, light intensity, and irradiation shape on temperature distribution. We find that it is difficult to achieve good therapeutic effect just by adjusting the volume fraction of nanoparticles and light intensity. To achieve good therapeutic effect, we propose a new irradiation shape, spot array light. This method can achieve a better temperature distribution by easily regulating the positions of spots for the tumor with a large aspect ratio or a small one. In addition, the method of irradiation with spot array light can better reduce the overheating at the bottom and top of the tumor than the full-coverage light or others such as ring light. This theoretical work presents a simple method to investigate the effects of irradiation shape on therapy and provides a far more controlled way to improve the efficacy of photothermal therapy

Controllable transition between optical bistability and multistability in graphene/dielectric/graphene structure

We theoretically investigated the controllable transition between optical bistability and multistability in graphene/dielectric/graphene structure for TE and TM polarizations. We show such a transition strongly depends on the Fermi energy of graphene, and thus, it can be controlled by adjusting the gate voltage applied on the graphene. In addition, we also show that the transition can be tuned by changing the thickness and permittivity of the dielectric layer, or by varying the wavelength and the incident angle of the input light. Furthermore, three S-type curves appear in our studied structure, which result in quadristability. Our results may find potential applications in optoelectronic devices

Theory for optical activity in monolayer black phosphorus under external magnetic field

We derive an analytical model for calculating the optical activity in monolayer black phosphorus under an external magnetic field. By optimizing the parameters, the circular dichroism can be comparable to that in previously reported chiral metamaterials in a broad angle range. Besides, the optical activity including the circular dichroism, the circular conversion dichroism and the circular birefringence can be tuned almost linearly via changing the applied magnetic field magnitude. These results show that our proposed model would possess potential applications in polarization optics, stereochemistry, and molecular biology

Thermal emission of one-dimensional conjugated photonic crystals heterojunction embedded with graphene

By means of characteristic matrix method, we make a theoretical investigation on the properties of thermal emission from one-dimensional conjugated photonic crystals heterojunction embedded with graphene. We find that the emissivity plots show sharp spectral peaks and narrow antenna-like angular lobes which show the excellent temporal coherence and spatial coherence. By optimizing the parameters, a close-to-unity emissivity can be achieved in our proposed structure. Furthermore, we demonstrate that the emissivity peak wavelength and emissivity values can be tuned by changing the chemical potential of graphene layer and the center wavelength of conjugated photonic crystals. The study shows that our proposed structure may find great application in infrared spectrometers and infrared gas sensors

Angle-insensitive mid-infrared photonic bandgap in one-dimensional photonic crystal containing single-material semiconductor hyperbolic metamaterial layers

Based on the phase variation compensation theory, we realize an angle-insensitive mid-infrared photonic bandgap (PBG) in a one-dimensional photonic crystal (1DPC) containing single-material semiconductor hyperbolic metamaterial layers. Under proper design, the bandwidth of the angle-insensitive (omnidirectional) mid-infrared PBG can reach 2.438 \upmu \hbox {m}. The designed 1DPC is a simple single-material system composed of undoped and doped InAs, which can be fabricated by the molecular beam epitaxy technology under the current experimental conditions. Besides, the angle-insensitive property of the designed mid-infrared PBG is quite robust against the layer thickness. This broadband angle-insensitive mid-infrared PBG would possess potential applications for mid-infrared quantum cascade lasers, mid-infrared gas detectors, mid-infrared photothermal imaging, and protein analysis