ABSTRACT
A terahertz beam imaging method was proposed that involves scanning a reflecting echelon with temporal-spatial mapping inversion based on self-developed translation-scan and rotation-scan temporal-spatial mapping (TTSM and RTSM) algorithms. The beam characteristics of a terahertz time-domain spectroscopy (TDS) system, such as its size, shape, and energy distribution, were obtained. Besides the weak terahertz beam emitted from a TDS system, this scheme is also suitable for imaging large-size terahertz or laser beams in time-domain systems where existing beam imaging is impractical.
ABSTRACT
A polarization-insensitive broadband terahertz (THz) metamaterial absorber is presented in this paper. The metamaterial absorber consists of several circular and rhombus metallic patches as a unit cell and a metallic ground plane separated by a polyimide dielectric layer. By increasing the number of circular and rhombus patches with different sizes, the operating bandwidth of the absorber is broadened because of the resonances of each single patch getting close enough and merging together in the frequency range. The simulated results show that the absorption bandwidth covers a broadband frequency range of 0.22-0.33 THz with the highest absorptivity of 99.93% at 0.3035 THz. The full width at half maximum is as wide as 0.155 THz, and the bandwidth of over 80% absorptivity is 0.1315 THz. This study promises applications in THz detection and communication systems, and the operation bandwidth is very convenient and compatible for electronic THz sources.
ABSTRACT
In this paper, we design a tunable strength multiband absorber consisting of a graphene metamaterial structure and a thick dielectric interlayer deposited on a metal ground plane. We investigate the tunable conductivity properties of the graphene metamaterial and demonstrate multiband absorbers with three absorption bands using a polyimide interlayer in the 0-2.25 THz range by numerical simulation. The results show that the mix absorptivity reached 99.8% at 1.99 THz, and the absorptive strength can be tuned with the modulation depth up to 84.2%. We present a theoretical interpretation based on a standing wave field, which shows that the field energy is localized inside the thicker spacer and then dissipated, effectively trapping the light in the metamaterial absorbers with negligible near-field interactions. The standing wave field theory developed here explains all the features of the multiband metamaterial absorbers and provides a profound understanding of the underlying physics.
ABSTRACT
Electromagnetic metasurface with many special electromagnetic properties can be utilized to manipulate electromagnetic wave propagation and reflection. If the metasurfaces were designed for coding, random, phase discontinuities, perfect absorber and so onï¼they can manipulate the scattering or the reflection of electromagnetic wave and achieve the reduction of the radar cross section(RCS). This paper mainly presents the recent progress concerning the reduction of RCS using non - directional scattering or the absorption characteristic in microwave and terahertz wave. The analysis results show that coding electromagnetic metasurface can disperse the reflection into a variety of direction by designing the specific coding sequences for different elements. The coding metasurface which are composed of different digital elements, and the reflection phase difference of these digital elements is constant in a wide frequency range, and higher bit coding metasurface can flexible manipulate electromagnetic wave. The random electromagnetic metasurface can achieve broadband phase shifter by adjusting the size parameters of array element, and can diffuse characteristic by scattering into random wave of the reflection peaks for metal target. Phase discontinuities metasurface can achieve anomalous or diffuse of wave because the phase distribution is not uniform at the surface. The absorber metasurfaces which are designed reasonably with the physical dimensions of the devices can reduce reflection by absorbing electromagnetic wave energy. So, the electromagnetic metasurfaces have a large potential application for radar stealth, broadband communications, imaging and so on. Finally, we discussed the future development of RCS reduction by using the electromagnetic metasurface. In order to satisfy the needs of practical application, the research of metasurface will continue development in broadband, flexible, large angle and other aspects.
ABSTRACT
In the present paper, the recent progress in terahertz metamaterials-based sensing is reviewed with the principle of metamaterial biosensor,metamaterial substrate, and structure design, respectively. The paper introduces the principle in detail, analyzes the sensitivity of the biosensor with the material and the thickness of the substrate and the structure of metamaterial. The analysis shows that we can enhance the sensitivity and resolution of biosensor by designing specific metamaterial structure, using low dielectric constant and low loss thin substrate, especially many materials have a specific response in the terahertz frequency. So, there is a large potential application for label-free sensing by using the terahertz metamaterials. This paper also presents the future development of THz metamaterial sensors.
Subject(s)
Biosensing Techniques , Terahertz ImagingABSTRACT
In order to obtain the different position temperature changes in the process of explosive casting accurate, stability and comprehensive, we designed the temperature monitoring system based on fiber Bragg grating spectral shift. Through the fiberoptic network, the system can monitor the different point temperature of melt-cast explosive real-time. According to the function of linear frequency shift of fiber Bragg grating wavelength with the grating of temperature, we get the temperature of different positions. Four channels share a broadband light source with a coupler. The Bragg wavelengths of the 5 gratings of each fiber are separated from each other. Using the gratings designed, spliced and packaged by our own, we can obtain temperature data through the demodulator. The temperature data was processed by the Origin to draw diagram time-temperature curve. The results show that the measured temperature data of the fiber Bragg grating can meet the requirements of experiment.
ABSTRACT
Study on surface-enhanced Raman scattering in the terahertz-band proved in that the terahertz-band Raman enhancement also exists. By studing principles of electromagnetic enhancement of surface-enhanced Raman scattering, using the finite difference time-domain method, the electromagnetic enhancement of surface enhanced Raman scattering of nano-particles irradiated by terahertz-wave was simulated, and the enhancement effect of terahertz waves was analyzed. Simulation experiments show that using finite-difference time-domain method could obtain effectively accurate simulation result of nano-particle scattering, proving that for terahertz waves, surface-enhanced effects on the surface of the nano-particle also exist. The results for surface enhanced Raman scattering extended from the visible and infrared to terahertz-band, and provide a basis for application of the combination of surface-enhanced Raman scattering and terahertz-wave.
ABSTRACT
In order to detect the content of a new kind of insensitive melting-cast explosive (DNAN), the system detected the THz characteristics wavelength of DNAN, and solved the content of DNAN by the Bill-Lambert law. Time coherent THz spectroscopy detection system was designed, in which the master system controlled stepper motor to get the micro-scanning of the photoelectric detector. The system parameters were calculated and derived for solving the content of DNAN, and THz characteristic spectrum of DNAN was obtained. Experiment used three methods to detect explosives samples with different content of DNAN, and the results show that the accuracy of this system is close to that of MINI-Z terahertz spectrometer currently broadly applied in THz spectroscopy detection equipment at home and abroad. On this basis, the optimization algorithm of characteristic absorption peak was designed, and by the origin software simulation analysis, it shows that the algorithm can further improve accuracy and stability of the detection system.
ABSTRACT
The authors present a one-dimensional calculation model of H3(+), and the time-dependent wavefunction was obtained by the symmetric split-operator method. The authors investigated the high-order harmonic generation (HHG) properties of H3(+) model exposed to 800 nm-wavelength ultrashort laser pulse. The effect of electron interaction on the HHG spectra is less profound than at the cut-off frequency. We also calculated the HHG spectra for different internuclear separation values close to realistic one. Most of the calculated cutoff frequencies are beyond the three-step model's prediction, and a preliminary scenario is suggested.
ABSTRACT
A large-mode-area polymer photonic crystal fiber made of polymethyl methacrylate with the cladding having only one layer of air holes near the edge of the fiber is designed and proposed to be used in surface plasmon resonance sensors. In such sensor, a nanoscale metal film and analyte can be deposited on the outer side of the fiber instead of coating or filling in the holes of the conventional PCF, which make the real time detection with high sensitivity easily to realize. Moreover, it is relatively stable to changes of the amount and the diameter of air holes, which is very beneficial for sensor fabrication and sensing applications. Numerical simulation results show that under the conditions of the similar spectral and intensity sensitivity of 8.3 × 10(-5)-9.4 × 10(-5) RIU, the confinement loss can be increased dramatically.
ABSTRACT
A kind of surface plasmon resonance sensor based on grapefruit photonic crystal fiber (PCF) filled with different numbers of silver nanowires has been studied in this paper. The surface plasmon resonance modes and the sensing properties are investigated comprehensively using the finite element method (FEM). The simulation results show that the intensity sensitivity is related to nanowire numbers and the distance between two nanowires. The optimum value obtained is 2,400 nm/RIU, corresponding to a resolution of 4.51 × 10(-5) RIU with a maximum distance of 2 µm. To a certain extent, the PCF filled with more nanowires is better than with just one. Furthermore, the air holes of grapefruit PCF are large enough to operate in practice. Moreover, the irregularity of the filled nanowires has no effect on sensitivity, which will be very convenient for the implementation of experiments.
Subject(s)
Biosensing Techniques/instrumentation , Citrus paradisi/chemistry , Equipment Design/instrumentation , Fiber Optic Technology/instrumentation , Nanowires/chemistry , Silver/chemistry , Surface Plasmon Resonance/instrumentationABSTRACT
A high-efficiency 1342 nm Nd:YVO4 laser in-band pumped at 914 nm is demonstrated for the first time. Using an all-solid-state Nd:YVO4 laser operating at 914 nm as pump source, 0.86 W output was obtained with 1.82 W absorbed pump power. Corresponding slope efficiency of 65.4% was the highest of Nd:YVO4 lasers operating at 1342 nm to the best of our knowledge. Effects of crystal's doping concentration and temperature on laser power and conversion efficiency were also investigated.
ABSTRACT
Single-shot laser induced breakdown spectroscopy (single-shot LIBS) has become one of the most important branches of material detection. The present article mainly focuses on analysis of the emission spectra of lead by quantitative methods. In the experiment, both qualitative and quantitative analysis are made to detect the content of lead in different material using single-shot LIBS with Q-switched Nd:YAG lasers whose pulse width is 10ns. In quantitative analysis, detections of the emission lines of pure lead with different pulse energies: 107, 139.2 and 171.5 mJ and different wavelengths: 1064, 532 and 1064/532 nm are made. Spectra under three conditions (1: same wavelengths and different pulse energies for single pulse lasers; 2: same pulse energy and different wavelength for single pulse lasers and 3: same wavelengths and different pulse energies for double pulse lasers) are acquired and compared.
ABSTRACT
We propose a novel photonic crystal fiber refractive index sensor which is based on the selectively resonant coupling between a conventional solid core and a microstructured core. The introduced microstructured core is realized by filling the air-holes in the core with low index analyte. We show that a detection limit (DL) of 2.02×10â»6 refractive index unit (RIU) and a sensitivity of 8500 nm/RIU can be achieved for analyte with refractive index of 1.33.
Subject(s)
Fiber Optic Technology/instrumentation , Manufactured Materials , Refractometry/instrumentation , Transducers , Crystallization , Equipment Design , Equipment Failure AnalysisABSTRACT
We designed a compact terahertz (THz) wave polarizing beam splitter based on a periodic bilayer structure, which operates over a wide THz wavelength range. Within a short length (about 1 mm), this polarizing beam splitter separates THz wave TE- and TM-polarized modes into orthogonal output waveguides. Results of simulations with the finite-element method show that 99.99% of the TE-polarized THz wave is deflected by the periodic bilayer structure (with 39.9 dB extinction ratio), whereas 99.58% of the TM-polarized THz wave propagates through the structure (with a 23.7 dB extinction ratio). Tolerance analysis reveals a large tolerance to fabrication errors.
ABSTRACT
Time-resolved optoacoustic technique offers a new ingredient in noninvasive monitoring of biological tissues. Due to the heterogeneous property of biotissue, different level of optical energy depositions generates different strength of the acoustic signal across the tissue. This makes it possible to probe the functional information tomographically inside the biological tissue. It becomes increasingly attractive as a hybrid non-invasive monitoring technique because it takes the advantages of high contrast feature delivered by the optical techniques and high penetration depth and resolution offered by the acoustical techniques. After a brief introduction of its theory, this paper reviews the state-of-the-art time-resolved optoacoustic methods that have been successfully applied in biomedicine, with a concentration on analytical monitoring and tomography.
