Generation of terahertz (THz) radiation has been a hot research topic in recent years. Plasmonic quantum cascade lasers (QCLs) are among the most compact and efficient sources to generate THz radiation. In this paper, we comprehensively study plasmonic QCLs designed based on the antenna-feedback structure to generate efficient radiation about the center frequency of 3 THz. By changing the geometric structure of the plasmonic cavity and using two-dimensional simulation, a minimum loss less than 5.9 cm?1 is achieved at the lasing frequency. It is also possible to control the orientation of the output beam either vertically or tilted by changing the geometry of the antenna design via chirped or non-chirped grating scheme. Moreover, the output characteristics of the QCL are simulated based on the three-level rate equations through which the dynamics of the laser, as well as the P-I curve, are investigated. Also, the gain spectra for two laser designs (with chirped and non-chirped gratings) are simulated and compared to each other. The results of this paper may provide deep insight into designing efficient laser sources in the THz region.
相似文献In this article, we demonstrate a tunable ultra-broadband metamaterial absorber (TUMA) in terahertz (THz) band which is based on the multilayered structure composed of an Au reflective layer, polyimide dielectric layers, and vanadium dioxide (VO2) periodic structures, respectively. We gain the tunable absorption spectra because of the room temperature phased-changed character of VO2. The relative bandwidth reaches to 81.2% and the absorption rate is over 90% at the frequency range of 1.63–3.86 THz when the temperature (t1) is 350 K, but when t1 = 300 K, the presented absorber is acted as a reflector whose absorption is small besides the frequency points of 9.75 THz and 9.81 THz. For the sake of comprehending the physical mechanism in-depth, the electric field (E-field) diagrams, the surface current distributions and the power loss density (PLD) of the TUMA are investigated. The influences of structural arguments and incident angle (θ) on the absorption are also analyzed. The emulated consequences show that the absorption spectrum can be regulated by changing structural parameters and incident angle and the tunable absorption regions can be obtained by altering the external temperature.
相似文献Understanding the mechanisms of light–matter interactions in ultra-small plasmonic nanoparticles (USNP) represents a major challenge because of the importance of size dependence and quantum effects. The plasmon resonance in such small metallic nanoparticles (< 5 nm) exhibits substantial deviation from classical theory predictions, with evident frequency shifts to a higher energy. This is due to the quantum nature of the free charge carriers and the dynamic response of metallic nanoparticle to the self-consistent electromagnetic fields. Such phenomena have so far been poorly understood in experiments while classical theory has mostly focused on nanostructures and sidestepped the size dependence. Here we report a quantum mechanical model of the metal permittivity to describe the USNP behaviour and experimental evidence. The proposed non-local quantum model of the permittivity for the propagation of plasmon waves in quantum-confined silver nanoparticles has no size limitations in the UNSP range.
相似文献We propose the use of the electron cloud generated by quasi-particle waves called polariton dipoles, which oscillated within a silicon microring-embedded gold grating system for quantum consciousness processing model. An embedded gold grating is coupled by a whispering gallery mode beam generated by a soliton pulse, from which the polariton waves oscillated with the plasma frequency at the Bragg wavelength. The excited polariton cloud by the external stimuli can be detected at the system output ports. The two states of the polariton (electron) are spin-up and spin-down that can process automatically and deliver to the network and cloud. In manipulation, the results obtained show the electron density increased by increasing the input power into the system. In application, the cell polariton cloud coupled by the external stimuli and patterned by the quantum cellular automata results, which localized in the cloud network and connected to the nerve cell access nodes. The coded polaritons connected to the nerve cell memory clouds, while the required commands are delivered to resonant cells via the network link. More stenographic codes can also be generated by other external stimuli sources, which can process similarly.
相似文献Terahertz metamaterial absorbers (MMA) have found wide scope of research prospective, remarkably in the development of multiband absorbers. Considerable applications are established using these multiband absorbers in THz imaging, wireless communication and bolometric detectors. The MMA was built on a GaAs substrate of 30 µm thickness and the hexagonal metallic pattern was etched out on a gold layer of 0.4 µm thickness on the top surface. The underlying ground layer is metallic backed. This design realizes the multiband (9-bands) of absorption in the spectral region from 0.56 to 0.92 THz. The multiband absorption mechanism of the absorber was examined by electric field dispersion analysis and impedance matching concept. From the established results, the absorber exhibits nine bands within a narrow frequency range and secures promising applications in hyperspectral imaging, clinical sensing and detection.
相似文献A metal nanowire placed in a dielectric hole is proposed to guide THz modified surface plasmon polaritons (MSPPs). In theory, the MSPP waveguide can guide THz wave with nano-scale mode width (570 nm) and simultaneously ultra-long propagation distance (2.4 m). Compared with conventional surface plasmon polaritons (SPPs) on a bare metal nanowire, the MSPPs’ mode nanoconfinement can be maintained by keeping a part of the mode field nearly unchanged. On the other hand, by modifying the rest of the mode field, the THz power inside the metal nanowire can be significantly reduced for MSPPs, which dramatically decreases the propagation loss (3 orders of magnitude).
相似文献In the fields of communication and sensing, resonance bandwidth is a very critical index. It is very meaningful to implement a broadband resonance device with a simple metamaterial structure in the terahertz band. In this paper, we propose a simple metamaterial structure which consists of one horizontal metal strip and two vertical metal strips. This structure can achieve an electromagnetically induced transparency-like (EIT-like) effect in the frequency range of 0.1~3.0 THz to obtain a transparent window with a resonance bandwidth as high as 1.212 THz. When the relative distance between two vertical metal strips is changed, the bandwidth can be effectively controlled. Furthermore, we found that the EIT-like effect can be actively adjusted by replacing vertical metal strips with photosensitive silicon.
相似文献Ensuring a good trade-off between high-quality factor (Q-factor) and polarization independency is a key challenge for designing practicable terahertz metamaterial devices. We propose a symmetric composite aluminum-structured metamaterial absorber to achieve high Q-factor beyond 80 and near-unity absorbance of arbitrary polarization waves in the terahertz regime. Ultrahigh Q-factor reaches 84, and polarization-independent absorption is as high as 99% for resonant frequency tuning from 7.58 to 8.97 THz, covering 14% of the standard THz gap. The geometric effect of the symmetric sublattice on resonant frequency tuning is analyzed. The large Q-factor and strong absorption by oblique incidence is discussed. Designed high-Q metamaterial perfect absorber has various applications, including terahertz hyperspectral imaging, filtering, and sensing.
相似文献A five-band polarization-insensitive perfect metamaterial absorber (PMA) is reported in this paper for THz detection and sensing applications. The proposed absorber is constructed using interconnected circular ring elements enclosed by a square loop. The ring elements are interconnected using short strip lines which increases the electrical length to offer resonance at the lower frequencies of the THz regime without increasing the electrical length. The proposed absorber has a footprint of 0.12 λeff?×?0.12 λeff where λeff is the effective wavelength calculated at the lowest operating frequency. The absorber provides 92%, 84%, 90%, 100%, and 100% absorption at 0.24, 0.56, 0.65, 0.82, and 0.95 THz, respectively. The proposed structure offers structural symmetry, and hence, it is polarization-insensitive. The proposed five-band absorber has good angular stability consistent with many research works reported in the literature and has a small frequency ratio of 1:2.3:2.7:3.4:3.9. The proposed absorber can be used as a permittivity sensor and its sensitivity is estimated to vary from 5.8 GHz/permittivity unit (PU) to 23.56 GHz/PU.
相似文献Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.
相似文献In this article, the design of a frequency reconfigurable broadband THz antenna based on vanadium dioxide (VO2) is investigated. Instead of being fed by the microstrip line directly, a windmill-shaped feeding structure is designed to provide a proximity-coupled feeding method. Many modes with contiguous resonant frequencies can be excited to obtain the wideband performance. The proposed antenna combines gold with metamaterial VO2. Thanks to insulator-metal phase transition characteristic of VO2 at phase transition temperature (68 °C), we can change the length of the resonant branches to realize frequency reconfiguration by changing the external temperature (T). The simulated results illustrate that when T = 50 °C (State I), such an antenna has a bandwidth of 35.2% (7.01–10 THz) with S11 below − 10 dB, and a maximum gain of 6.62 dBic. When T = 80 °C (State II), it has a bandwidth of 21.8% (5.77–7.18 THz) with S11 below − 10 dB, and a maximum gain of 4.49 dBic. Thus, we realize a design of a proximity-coupled antenna with reconfigurable wideband over the THz band.
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In this article, a terahertz absorber tuned by temperature field with a newfangled structure is presented, which comprises the mercury resonators. In this scheme, temperature (T) build-up will lead the mercury stored in the bottom slot to expand through the columniform hole and be full of the upper central cross container, which can transform the absorption bands of such an absorber. The simulated results manifest that when T is increased from 0 to 25 °C, the dual-frequency absorption points (2.59 THz, 3.03 THz) and a narrow absorption region over 90% (6.54–7.10 THz), whose relative bandwidth (RB) is 7.9%, will be tailored to a single-frequency point absorption (3.12 THz) and a broadband absorption area (6.00–7.21 THz, and RB = 18.3%). For figuring out the property of the absorber mentioned above, the impacts of incident and polarization angles along with some relevant parameters of the structure on the absorption property are investigated. In addition, for plainly expounding the physical mechanism of absorption, the distributions of the surface current diagrams of the presented absorber are calculated, as well as the electric field diagrams, the magnetic field diagrams, the power loss density diagrams, and the power flow density diagrams. The proffered scheme in this article may offer a novel idea for realizing the reconfigurable absorbers.
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