Properties of terahertz wave generated by the metallic carbon nanotube antenna

The properties of terahertz(THz)radiation pulses emitted by a metallic,large aspect ratio carbon nanotube antenna have been studied both in the THz waveforms and field distribution.The peak THz field up to 2.66 and 1.26 kV/cm are observed at the probe points.The proposed antenna is designed to operate for dual frequency applications from 2.36 to 2.58 THz and from 7.27 to 7.5 THz for less than-10 dB return loss.     

Full vectorial feature of second-harmonic generation with full Poincaré beams

We demonstrate the full vectorial feature of second-harmonic generation(SHG), i.e., from infrared full Poincarébeams to visible full Poincaré beams, based on two cascading type I phase-matching beta barium borate crystals of orthogonal optical axes. We visualize the structured features of the vectorial SHG wave by using Stokes polarimetry and show the interesting doubling effect of the polarization topological index, i.e., a low-order full Poincaré beam is converted to a high-order one. However, the polarization singularities of both C points and L lines are found to keep invariant during the SHG process. Our scheme could offer a deeper understanding on the interaction of vectorial light fields with media and can be generalized to other nonlinear optical effects.     

CČerenkov second-harmonic generation by nondiffracting Bessel beams in bulk optical crystals

A new method of optical second-harmonic generation (SHG) in bulk media is proposed, using Bessel beams which realize Cerenkov phase matching. Single-domain crystals are presently considered. For noncollinear emission the scheme has the advantage of achieving conversion efficiencies of typically about double those achieved with unfocused Gaussian beams, over the same temperature bandwidth. The harmonic radiation is analysed using a Hankel transform-based spectral method. Numerical examples are given based on the crystal KNbO3, and possible experimental arrangements are suggested for the practical implementation of this method.     

Theoretical analysis for sound wave scattering by parallel cylindrical tubes in boilers

1 IntroductionWith the constant increase of boiler load and fuel consumption in recent years, it is moreand more difficult for traditional soot cleaning techniques to solve the ajsh deposit and fossilsedimellt in boilers. Sonic soot cleaning has been proved to be a new and effective technique,but its application study is far in advance than the basic research because of its increasinglyand urgently marketing needs. Some unsolved basic problems would bring us more and moredifficulties before th…     

Composite vortex beams by coaxial superposition of Laguerre–Gaussian beams

We propose the generation of novel composite vortex beams by coaxial superposition of Laguerre–Gaussian (LG) beams with common waist position and waist parameter. Computer-generated holography by conjugate-symmetric extension is applied to produce the holograms of several composite vortex beams. Utilizing the holograms, fantastic light modes including optical ring lattice, double dark-ring and double bright-ring composite vortex beams etc. are numerically reconstructed. The generated composite vortex beams show diffraction broadening with some of them showing dynamic rotation around beam centers while propagating. Optical experiments based on a computer-controlled spatial light modulator (SLM) verify the numerical results. These novel composite vortex beams possess more complicated distribution and more controllable parameters for their potential application in comparison to conventional optical ring lattice.     

Calculation of ion energy distributions of argon excimer ions generated in helicon plasma

A program is developed to calculate the ion energy distributions （IEDs） of Ar2^＋ making use of a simplified kinetic model with a combination of Monte Carlo method. Several coefficients are used to realize good match between the calculated and measured results. Some important assumptions are confirmed： argon excimer ions have short lifetime, hence they are formed in a short range before the collecting electrode. The excimer ions that encounter collisions will be discarded because they turn to other ion species after they collide with argon atoms. From the calculated results some plasma parameters such as the cross section or neutral density in discharge could be evaluated.     

Investigation of KTiOPO_4 nanocrystals by means of second-harmonic light emission

The finding of nonlinear nanometric-sized probes is of key importance for the development of nonlinear microscopy in physical as well as biological sciences.We isolate nonlinear KTiOPO_4 nanocrystals and study them by second-harmonic generation microscopy(SHGM)and atomic force microscopy(AFM) independently.With both polarization analysis and defocused imaging of the emitted second harmonic field,we extract the Euler angles of the crystalline axes of a single nanocrystal.A balanced coherent optical homodyne detection shows tire coherent nature of the nanocrystal nonlinear emission and allows a phase measurement of the emitted second-harmonic field.These features make the KTiOPO_4 nanocrystal a good candidate for a vectorial probe of electromagnetic near fields.     

In situ observation of cell-detachment process initiated by femtosecond laser-induced stress wave

When a stress wave generated by focusing a femtosecond laser is loaded on an animal cell adhered on a substrate, the cell is detached from the substrate. There are two possible mechanisms for the cell detachment: (a) The cell is detached from a scaffold coated on a glass plate, and (b) the cell is detached from the glass plate with the scaffold. In this work, we have studied the cell-detachment mechanism by visualizing the scaffold with a fluorescence probe of quantum dots. When the cell was detached from the substrate, fluorescence from the scaffold simultaneously disappeared from the glass plate, although the scaffold was not irradiated by the laser. This indicates that detachment due to the stress wave is attributed to mechanism (a). On the other hand, when the cell was detached from the substrate by a trypsin treatment, the fluorescence from the scaffold remained, suggesting mechanism (b). By comparing both results, it is considered that physiological damage of the cell membrane during the detachment process by femtosecond laser-induced stress wave is less than that due to the trypsin treatment.     

Vortex and anti-vortex compositions of exact elegant Laguerre–Gaussian vector beams

Reformulation of conventional beam definitions into their bidirectional versions and use of Hertz potentials make beam fields exact vector solutions to Maxwell’s equations. This procedure is applied to higher-order elegant Laguerre–Gaussian beams of transverse magnetic and transverse electric polarization. Their vortex and anti-vortex co-axial compositions of equal and opposite topological charges are given in a closed analytic form. Polarization components of the composed beams are specified by their radial and azimuthal indices. The longitudinal components are common for beam compositions of both types; meanwhile, their transverse components are different and comprise two—nonparaxial and paraxial—separate parts distinguished by a paraxial parameter and its inverse, respectively. The new solutions may appear useful in modeling and tailoring of arbitrary vector beams.     

Three-dimensional tomographic reconstruction of ultrashort free electron wave packets

We present a tomographic technique based on Photoelectron Angular Distributions (PADs) measured by Velocity-Map-Imaging (VMI) to reconstruct the three-dimensional shape of ultrashort free electron wave packets obtained from 1+2 Resonance Enhanced Multi-Photon Ionization (REMPI) of potassium atoms. To this end the laser pulse is rotated about its propagation direction and a set of PADs are recorded at different rotation angles. The tomographic reconstruction technique is described and results for linear and elliptical polarization are presented. Results for linearly polarized light producing cylindrically symmetric electron wave packets confirm the validity of our method whereas elliptically polarized light serves as a prototype for polarization-shaped laser pulses.     

Characteristics of γ-Al2O3 nanoparticles generated by continuous-wave laser ablation in liquid

Laser ablation in liquid is one of the most widely investigated methods for generating various nanoparticles (NPs) that are difficult to produce using other means. In this paper, we report the generation of Al-oxide NPs by continuous-wave (CW) fibre laser ablation of corundum (α-Al₂O₃) target submerged in deionised water. The effects of CW fibre laser power and radiation time have been investigated. Characterisation of the NPs generated, in terms of size, size distribution, shape, chemical composition, and phase structure, was carried out by means of high-resolution transmission electron microscopy (HR-TEM), high angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the average size of Al-oxide NPs, in the range of 17 to 29 nm, increased with increasing the laser power and laser exposure time, and the NPs are dominated by stoichiometric γ-Al₂O₃ with a minor phase of α-Al₂O₃. The mechanism involved in the CWLAL is also discussed.     

Calculation of Aberrations Introduced by a Crystal Components

建立了折射光线轨迹的软件包和提出了波象差的计算方法．利用这个软件包，分析了双焦透镜的各类象差和象差与入射角的关系．这个软件包的特点是各种物理量的计算十分清晰，它为改进晶体元件的设计提供了理论依据．     

Rogue wave solutions of the vector Lakshmanan–Porsezian–Daniel equation

We use a nonrecursive Darboux transformation method to obtain a special hierarchy of rogue wave solutions of the vector Lakshmanan–Porsezian–Daniel equation, which can govern the propagation of ultrashort optical pulses in a long-haul telecommunication fiber. In terms of the exact rational solutions, we demonstrate several interesting rogue wave dynamics such as rogue wave doublets, quartets and sextets. The modulation instability responsible for the excitation of rogue waves from an unstable continuous background in such a complex nonlinear system is also discussed.     

The rapid prototyping of textured amorphous surfaces for the graphoepitaxial deposition of CdTe films using focused ion beam lithography

Cadmium telluride films deposited on amorphous substrates exhibit a grain structure characterized by [111]-oriented grains, but where the in-plane grain orientation is randomized due to the absence of epitaxy. Here, we explore the viability of promoting an in-plane grain alignment through graphoepitaxy. Fifteen different substrate surface textures were fabricated using focused ion beam lithography. This approach allows for the side-by-side deposition of surface textures where both the areal extent and depth of the surface features are varied in a systematic manner. CdTe films deposited overtop these textures show grain structures with dramatic variations, revealing that particular length scales have the most pronounced effect on the grain structure.     

Enhancement of resolution and quality of nano-hole structure on GaN substrates using the second-harmonic beam of near-infrared femtosecond laser

By using a second harmonic of near infrared femtosecond (fs) laser (λ=387 nm, 150 fs) with high NA objective lens, fabrication resolution has been greatly improved in nano-fabrication of wide band-gap semiconductor gallium nitride (GaN). We have carried out a wet-chemical-assisted fs laser ablation method, in which the laser beam is focused onto a single-crystal GaN substrate immersed in a concentrated hydrochloric (HCl) acid solution. A two-step processing involving irradiation with a fs laser beam in air followed by wet chemical treatment is also performed for comparison. In the wet-chemical-assisted ablation, theoretical diameters of ablation craters are calculated as a function of pulse energy by assuming that the reaction is based on two-photon absorption. In lower energy, the calculated curve is close to the experimental value, while the actual measured diameters in the region of higher energy are larger than calculated values. In the condition of the highest fabrication resolution, we obtained ablation craters smaller than 200 nm at full width at half maximum. We have also demonstrated the fabrication of two-dimensional (2D) periodic nanostructures on surface of a GaN substrate using the second harmonic single fs-laser pulse. Uniform ablation craters with the size as small as 410 nm in diameter are arranged with a periodicity of 1 μm. Such structures are applicable to 2D photonic crystals which improve the light extraction efficiency for blue LEDs in the near future.     

VPγ radiative decay of resonances dynamically generated from the vector meson–vector meson interaction

We evaluate the radiative decay into a vector, a pseudoscalar and a photon of several resonances dynamically generated from the vector–vector interaction. The process proceeds via the decay of one of the vector components into a pseudoscalar and a photon, which have an invariant mass distribution very different from phase space as a consequence of the two vector structure of the resonances. Experimental work along these lines should provide useful information on the nature of these resonances.     

Flexible and high-efficiency generation of arbitrary vector vortex beams on hybrid-order Poincaré sphere

We propose theoretically and verify experimentally a compact optical configuration to directly generate arbitrary vector vortex beams on a hybrid-order Poincaré sphere with good flexibility and high efficiency based on a reflective phase-only liquid crystal spatial light modulator(LC-SLM). The conversion system, consisting of an LC-SLM and a quarter-wave plate, can be considered a flexible dielectric metasurface to simultaneously modulate inhomogeneous polarization and helical phase-front. This approach has some advantages, including a simple experimental setup, good flexibility, and high efficiency. Orthogonally polarized modes alignment and an explicit superposition existing in the conventional method are not necessary in the proposed method, which exhibits potential applications in many advanced domains.     

Study of characteristics of ultrasound pulse generated by a laser pulse

I.IntroductionThegenerationofacousticpulsebylaserirradiationofametalsurfacewasfirstsuggestcdbyWhitein1963[1l.SincethatdateLaserU1trasoundtechniquchasbeendcvclopedrapidly.Becausethistechniquehasanumberoftechnicalfcatures,suchasnon-contact,highbandwidth,highhme-spacia1resolution,quantitativeteshng,generationoflongitudinal,shcarandRay1cighwaves(simu1taniously),andsoon,ithasbccnwidelyapp1icdtomcasurementsofmatcrialproperties,detectionofdefects,andcalibrationoftransd.ccrsl'-'o].Inordertodcve1opth…     

Effect of vectorial nature on spectral anomalies of ultrashort pulsed beams from a hard-edged aperture

Based on the vectorial Rayleigh–Sommerfeld diffraction integrals, the analytical expression for the spectral intensity of a vectorial nonparaxial ultrashort pulsed Gaussian beam diffracted at a rectangular hard-aperture is derived. The results of the far-field and paraxial cases can be regarded as special cases of the general expression. Effect of vectorial nature on spectral anomalies of ultrashort pulsed beams passing through a hard-edged aperture is analyzed in detail. It is shown that the spectral switch near the phase singularity, which is predicated under the condition of the scalar paraxial theory, disappears with the increasing effect of the vectorial and nonparaxial nature.