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The theory of photoacoustic tomography imaging using an acoustic lens imaging system has been investigated, and the photoacoustic (PA) Fourier imaging property of an acoustic lens is presented. The theoretical results show that an acoustic lens is able to realize two-dimensional PA Fourier imaging and the focal depth of the acoustic lens is 20 mm. The PA signals with the advantage of time resolution can be resolved in time domain by time-resolved technique. Therefore, this long focal depth characteristic of the acoustic lens can be combined with time-resolved technique to realize PA tomography imaging. It is demonstrated by experiments that this method is able to provide PA tomography images of biological tissue. The images are clear and contrast sharply with their backgrounds. The depth resolution is 1.54 mm. [ABSTRACT FROM AUTHOR]

A tunable wavelength filter based on plasmonic metal-dielectric-metal waveguide with optofluidics pump system has been proposed and numerically investigated. The finite difference time domain method with perfectly matched layer-absorbing boundary condition is adopted to simulate and study their properties. An analytical solution to the resonant condition of the structure is derived by means of the cavity theory. It is found that the resonant wavelength of the filter is easily tuned in a broadband by manipulating the fluid filled in the cavity. Both analytical and simulative results reveal that the resonant wavelengths are proportional to the volume and refractive index of liquid in the cavity and are related to the structure of the filter. The resonant wavelengths of this structure can be changed from 1,106 to around 1,800 nm in this paper. The waveguide filter may become a choice for the design of devices in highly integrated optical circuits. [ABSTRACT FROM AUTHOR]

Abstract: We present and analyze novel vertical rectangular resonator filter based on metal–insulator–metal (MIM) structure. Finite difference time domain (FDTD) method is used in numerical analysis in this paper. Calculations and simulations reveal that the vertical rectangular resonator behaves as plasmonic filter. The free spectral range (FSR) for vertical rectangular resonator is twice as wide as that for transverse rectangular resonator. The aperture-coupled vertical rectangular resonator is also studied in detail. Investigation shows that the transmission curve contains narrow and high peaks, which can be up to 92%. [Copyright &y& Elsevier]

A graphene-based metamaterial structure with tunable plasmon induced transparency (PIT) effect is numerically and theoretically researched in this paper. Both the collinear and parallel graphene strips serve as bright mode and a PIT window emerges due to the weak hybridization between them. The transparency window can be tuned by not only adjusting the geometry parameter of the structure but also changing the chemical potential of the graphene strips. Different from the reported tunable PIT system, the spectra width and resonance strength can be tuned with the PIT peak at a fixed frequency in this research. Moreover, the Q factor can be affected by the distance between two bright modes and a figure of merit (FOM) as high as 15.20 can be achieved in this research. These properties expand the application for PIT phenomenon in mid-infrared metamaterial devices, such as filter, modulator and sensor. [ABSTRACT FROM AUTHOR]

Dynamically tunable plasmonic multi-functional is particularly desirable for various nanotechnological applications. In this paper, graphene nano-sheet pair arrays separated by a substrate, which can act as a dynamically tunable plasmonic band stop filter with transmission at resonance wavelength lower than 1%, a high sensitivity refractive index sensor with sensitivity up to 4879 nm/RIU, figure of merit of 40.66 and a two circuit optical switch with the modulation depth up to 0.998, are proposed and numerically investigated. These excellent optical performances are calculated by using FDTD numerical modeling and theoretical deduction. Simulation results show that a slight variation of chemical potential of the graphene nano-sheet can achieve significant resonance wavelength shifts. In additional, the resonance wavelength and transmission of this plasmonic device can be tuned easily by two voltages owing to the simple patterned graphene. These studies may have great potential in fabrication of multi-functional and dynamically tunable optoelectronic integrated devices. [ABSTRACT FROM AUTHOR]

A tunable terahertz filter based on graphene plasmonic all-dielectric metasurfaces is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Especially, hybrid all-dielectric metasurfaces are used to make a whole single-sheet graphene forms two different conductivity patterns with the same gate voltage. The simulated results show that resonance wavelength is shifted significantly with the change of gate voltage. Besides, the transmittance spectra are also shifted with the change of the width of SiC, and the filter shows a polarization-dependent modulation property for the length and the width of SiC being 480 and 320 nm, respectively. In addition, the filter can be applied for refractive sensing because the transmittance spectra are shifted with the change of the background refractive index. The study could provide availability for versatile tunable terahertz graphene plasmonic metasurfaces. [ABSTRACT FROM AUTHOR]

We report the observation of an analog of double electromagnetically induced absorption (EIA) in a plasmonic system consisting of two disk resonators side-coupled to a discrete metal-insulator-metal (MIM) waveguide. The finite-difference time-domain (FDTD) simulation calculations show that two absorption windows are obtained and can be easily tuned by adjusting the parameters of the two resonance cavities. The consistence between the coupled-model theory and FDTD simulation results verify the feasibility of the proposed system. Since the scheme is easy to be fabricated, our proposed configuration may thus be applied to narrow-band filtering, absorptive switching, and absorber applications. [ABSTRACT FROM AUTHOR]

We firstly investigate plasmon induced transparency (PIT) effect in a metal–dielectric–metal (MDM) waveguide coupled to a single loop stub resonator by finite difference time domain method (FDTD). Compared with previous PIT sup based on MDM waveguide, PIT phenomena can be realized in a single plasmonic composite nanocavity without employment of additional optical elements. Plasmon induced transparency windows can be controlled by adjusting the geometrical parameters of the vertical branches or the horizontal branch in the plasmonic structure. The red-shift of PIT peak is almost linearly proportional to the refractive index of the horizontal branch. This plasmonic system takes the advantages of easy fabrication and compactness. The results may pave a way for the dynamic control of light in highly integrated optical circuits, which can realize ultrafast switching, light storage and nanosensor devices. [ABSTRACT FROM AUTHOR]

A method of the analog of electromagnetically induced transparency (EIT) in plasmonic metal–dielectric–metal (MIM) waveguide is proposed by using two asymmetric side-coupled cavities and simulated by Finite-difference time-domain (FDTD). The simulation results show that the transparency peak of EIT is very sensitive to the width difference of two cavities and the difference of coupling distances of two cavities with the bus. Furthermore, we find that high transmission of EIT-peak usually accompanies a relatively low quality factor. These properties of our novel plasmonic structure would pave the way for highly integrated optical circuits and optical information processing. [ABSTRACT FROM AUTHOR]

The third-order nonlinearity of five stable organic radical species with nitronyl nitroxide group was investigated using a femtosecond optical Kerr gate method. The magnitudes of their second hyperpolarizability were measured at around 10[sup -34]-10[sup -32] esu. The influence of the subtle chemical change of the molecular structure was explored. The experimental results were compared with theoretical calculation. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) is a temperature phase change material that has metallic properties at high temperatures and insulation properties at room temperature. In this article, a novel device has been designed based on the dielectric metasurface consisting of VO2 and graphene array, which can achieve multiple functions by adjusting temperature and voltage. When the temperature is high (340 K), the device is in the absorption state and its absorptivity can be dynamically controlled by changing the temperature. On the other hand, the device is in the polarization state under room temperature, and the polarization of electromagnetic waves can be dynamically controlled by adjusting the voltage of graphene. This device can achieve a broadband absorber (the maximum absorptance reaches 99.415% at wavelengths ranging from 44 THz to 52 THz) and high polarization conversion efficiency (>99.89%) in the mid-infrared range, which has great advantages over other single-function devices. Our results demonstrate that this multifunctional device may have widespread applications in emitters, sensors, spatial light modulators, IR camouflages, and can be used in thermophotovoltaics and wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrated a low-loss and high-transmission analogy of electromagnetically induced transparency based on all-dieletric metasurface. The metamaterial unit cell structure is composed of two mutually perpendicular silicon nanoscale bars. Under the joint effects of the neighboring meta-atoms' coherent interaction and significant low absorption loss, the transmission and the Q-factor can reach up to 93 % and 139, respectively. Moreover, we use the coupled harmonic oscillator model to analyze the near field interaction between the two elements in the electromagnetically induced transparency (EIT) metamaterial unit cell qualitatively and the effects of parameters on EIT. The figure-of-merit of 42 and the group delay of 0.65 ps are obtained. These characteristics make the metamaterial structure with potential to apply for ultrafast switches, sensor, and slow-light devices. [ABSTRACT FROM AUTHOR]

We have demonstrated the analogy of electromagnetically induced transparency in plasmonic nanodisk with a square ring resonator. A reasonable analysis of the transmission feature based on the temporal coupled-mode theory is given and shows good agreement with the Finit-Difference Time-Domain simulation. The transparency window can be easily tuned by changing the geometrical parameters and the insulator filled in the resonator. The transmission of the resonator system is close to 80% and the full width at half maximum is less than 46 nm. The sensitivity of the structure is about 812 nm/RIU. These characteristics make the new system with potential to apply for optical storage, ultrafast plasmonic switch and slow-light devices. [ABSTRACT FROM AUTHOR]

In a single quantum dot (QD) system connected with ferromagnetic electrodes, the electron transport properties, assisted by the thermal and Fock state optical fields, are theoretically studied by the Keldysh nonequilibrium Green's function approach. The results show that the evolution properties of the density of state and tunneling current assisted by the Fock state optical field, are quite different from those of the thermal state. The photon sideband shift decreases monotonously with the increase in the electron–photon coupling strength for the case of the thermal state, while the shift is oscillatory for the case of the Fock state. Negative differential conductance (NDC) appears obviously in a QD system contacted with parallel (P) and antiparallel (AP) magnetization alignment of the ferromagnetic electrode leads, assisted by the Fock state optical field in a wide range of electron–photon interaction parameters. Evident NDC usually only arises in an AP configuration QD system assisted by the thermal state optical field. The results have the potential to introduce a new way to actively manipulate and control the single-electron tunneling transport on a QD system by the quantum states of the optical field. [ABSTRACT FROM AUTHOR]

In this paper, using the particle-number-resolved master equation, the properties of full counting statistics (FCS) are investigated for a single quantum dot (QD) system interacting with optical fields in the thermal state, Fock state, coherent state, and coherent state with random phase. In these diverse quantum states of optical fields, average tunneling currents have different step shoulder heights at a lower bias voltage with the same light intensity, and a staircase-shaped current can be induced unexpectedly in vacuum state optical field. The characteristics of the Fano factor and skewness in the coherent state differ from those in all of the other cases. For avalanche-like transport at a lower bias voltage, the mechanism is a dynamical channel blockade in a moderate electron–photon interaction regime. There is a pronounced negative differential conductance that results from tuning the phase of the coherent state optical field in a symmetric QD system. [ABSTRACT FROM AUTHOR]