The influence of the geometry of micro-patterned thin films on the effective permeability and resonance frequency by domains development

For the application in high-frequency micromagnetic devices, the permeability and resonance frequency of ferromagnetic components is of high interest. It is dominantly influenced by different factors, the external field and direction and the domain distribution, shape and orientation. By the use of micromagnetic simulation, the domain pattern in films was determined and the effective permeability was calculated. The results of the calculations were compared with the domain shape of patterned microstructures of thin FeCoTaN-films, which were deposited onto oxidised silicon substrates by reactive r.f.-magnetron sputtering by employing 6-in Fe₃₇Co₄₆Ta₁₇ targets. To achieve a high-frequency suitability, the films have to be annealed in a static magnetic field of 50 mT between 400 and 500 °C, which are typical temperatures used in CMOS processes, to induce an in-plane uniaxial anisotropy needed for the high-frequency performance. Magnetic softness was obtained by producing amorphous or nanocrystalline films, and additionally, by aspiring low magnetocrystalline anisotropies for, e.g., certain Fe/Co fractions. The unpatterned films with a lateral dimension of 5×5 mm² were measured in a strip line permeameter in a frequency range up to 5 GHz and exhibited ferromagnetic resonance frequencies between 2 and 2.5 GHz within a low-loss permeability spectrum (low width of imaginary part of permeability). For possible integrations in passive microelectronic components the films were patterned to a few tenths of micrometers by near ultra-violet lithography and plasma beam etching, and then consequently annealed to obtain the static and dynamic magnetic properties. To influence the amount of closure domains, designs were conceived to influence the domain formation by creating additional internal boundaries. As a result, the ferromagnetic resonance frequency and the effective permeability are strongly driven by internal and external boundaries.     

Remote fiber sensor based on cascaded Fourier domain mode-locked laser

We propose a high-speed remote fiber Bragg grating (FBG) sensor interrogation system based on a 1.3-μm cascaded Fourier-domain mode-locked (FDML) laser. It consists of multiple FBGs connected to an optical circulator in the laser cavity. The cascaded FDML laser with these multiple FBGs is operational when the scanning frequency of the fiber Fabry-Perot tunable filter matches the fundamental frequency of the laser cavity. Each FBG provides a separate laser cavity for the FDML laser. The scanning frequencies of each laser cavity are 30.5314, 31.5393, 32.7108, and 33.8023 kHz. Using the cascaded FDML laser, we measure the performance of the long-distance static strain FBG sensor interrogation system in both the time and spectral domains. The slope coefficients of the measured relative wavelength difference and the relative time delay from the static strain are found to be 0.95 pm/μstrain and 0.15 ns/μstrain, respectively. We also demonstrate the dynamic response of the interrogation system with 80-Hz modulation strain using the cascaded FDML laser. Thus, an FBG sensor interrogation system for high-speed and high-sensitivity long-distance monitoring systems can be realized using a cascaded FDML laser.     

Synthesis of multi-wall carbon nanotubes by copper vapor laser

Synthesis of multi-wall carbon nanotubes in a 1473 K furnace using a copper vapor laser (CVL) is reported. The operating parameters of this laser, i.e. a high fluence at the focal point and an extremely high frequency of 10 kHz, distinguished it from common laser sources in the synthesis of CNTs. Therefore, the unexpected experimental findings, the formation of MWNTs instead of the generally reported SWNTs, would be verified by these two notable parameters. Electron microscopy beside Raman spectroscopy illustrates the presence of multi-wall carbon nanotubes in the resulting product.     

Acceleration of electrons by a Bessel-Gaussian beam in vacuum

The acceleration of electrons by using a Bessel-Gaussian (BG) beam in vacuum is studied. It is shown that the axial electric field of a linearly or circularly polarized BG beam of order n = 1 can be used to accelerate electrons. The general features of the acceleration of electrons by using a linearly or circularly polarized BG beam, such as the transversal and axial electric-field components, phase velocity, slippage distance, accelerating potential, and energy gain etc., are analyzed.     

Real-time focus control in broad flat field laser material processing

Broad flat field laser scanning is critical to the success of laser material processing, used in techniques such as rapid prototyping & manufacturing (RP&M) and micro-machining. For these techniques it is necessary to produce high-performance optical systems that can fulfill the need for a smaller focused spot size over broad, flat field scanning areas. This paper concentrates on the issues of defocus error compensation. A dynamic focusing system is designed, intended primarily for broad flat field galvanometric laser scanning applications. Key technologies are described in detail; corresponding solutions have been used to design and produce a CO₂ infrared optical focusing system, which is capable of scanning a focused spot size of 120 μm or less over areas up to 500 mm².     

Output characteristics of a cataphoresis He–Sr recombination laser

A cataphoresis discharge tube of 7 mm inner diameter and 38 cm active length was designed and made for the He–Sr⁺ laser. The cataphoretic input of uniform distribution of strontium vapor concentrations along the active region was realized by the cataphoresis effect and the slow flowing (0.5 nl/h) of helium buffer gas. The strontium ionic recombination laser at 430.5 nm and the R–M transition laser at 1.03 μm were obtained with the modified Blumlein circuit by high-frequency longitudinal pulsed discharge. The laser components are concentrated on the 430.5 nm wavelength. Dependences of working parameters such as the pulse frequency, the supply voltage, and the helium pressure on laser output characteristics were measured and discussed. The maximum laser output power of 819 mW and specific power of 56 mW/cm³ were obtained, respectively.     

Ab-initio calculation of optical properties of AA-stacked bilayer graphene with tunable layer separation

Density functional theory based calculations revealed that optical properties of AA-stacked bilayer graphene are anisotropic and highly sensitive to the interlayer separation. In the long wave length limit of electromagnetic radiation, the frequency dependent response of complex dielectric function becomes vanishingly small beyond the optical frequency of 25.0 eV. Besides, static dielectric constant shows a saturation behaviour for parallel polarization of electric field vector when interlayer spacing is greater than 2.75 Å. As a consequence, an appropriate modification of effective fine structure constant is observed as a function of layer separation. Moreover, the bilayer systems are highly transparent in the optical frequency range of 7.0–10.0 eV. The electron energy loss function exhibits two different in-plane collective (plasmon) excitations and a single out of plane plasmon excitation. The spectral nature of different frequency dependent optical properties is observed to be very similar to that of the monolayer pristine graphene apart from their exact numerical values.     

A thin film magnetic field sensor of sub-pT resolution and magnetocardiogram (MCG) measurement at room temperature

We developed a very sensitive high-frequency carrier-type thin film sensor with a sub-pT resolution using a transmission line. The sensor element consists of Cu conductor with a meander pattern (20 mm in length, 0.8 mm in width, and 18 μm in thickness), a ground plane, and amorphous CoNbZr film (4 μm in thickness). The amplitude modulation technique was employed to enhance the magnetic field resolution for measurement of the high-frequency field (499 kHz), a resolution of 7.10×10^?13 T/Hz^1/2 being achieved, when we applied an AC magnetic field at 499 kHz. The phase detection technique was applied for measurement of the low frequency field (around 1 Hz). A small phase change was detected using a dual mixer time difference method. A high phase change of 130°/Oe was observed. A magnetic field resolution of 1.35×10^?12 T/Hz^1/2 was obtained when a small AC field at 1 Hz was applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signal including typical QRS and T waves, and compared the MCG with a simultaneously obtained conventional electrocardiogram (ECG) signal.     

Single pulse near field study on a Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure by using a femtosecond laser

Single pulse near field study on a Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure was experimentally investigated with a laser pulse width of 200 fs at a wavelength of 775 nm. For the near field experiments, we have used polystyrene colloidal particles of 700 nm diameter deposited by spin coating on top of the multilayer structure, as well on top of Co (50 nm) and Cu (50 nm) thin films. The diameter and the morphologies of the holes were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). We have estimated the fluence thresholds values for the near field and discuss their values in respect with the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. We compare the depths and the widths of the holes obtained at the same peak laser fluence for the Co thin film (50 nm), Cu thin film (50 nm) and Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure. Depending on the laser fluence, the ablation depth can reach the first, the second, or the third layer. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain (FDTD) by using the RSoft software. This type of a selective distribution of the ablation depth, in the near field regime, of a planar metal/dielectric interface can open new perspective in the excitation of propagating surface plasmons.     

Surface treatment of CFRP composites using femtosecond laser radiation

In the present work, we investigate the surface treatment of carbon fiber-reinforced polymer (CFRP) composites by laser ablation with femtosecond laser radiation. For this purpose, unidirectional carbon fiber-reinforced epoxy matrix composites were treated with femtosecond laser pulses of 1024 nm wavelength and 550 fs duration. Laser tracks were inscribed on the material surface using pulse energies and scanning speeds in the range 0.1–0.5 mJ and 0.1–5 mm/s, respectively. The morphology of the laser treated surfaces was investigated by field emission scanning electron microscopy. We show that, by using the appropriate processing parameters, a selective removal of the epoxy resin can be achieved, leaving the carbon fibers exposed. In addition, sub-micron laser induced periodic surface structures (LIPSS) are created on the carbon fibers surface, which may be potentially beneficial for the improvement of the fiber to matrix adhesion in adhesive bonds between CFRP parts.     

Interaction of ultrashort elliptically polarized laser pulses with nonlinear helical photonic metamaterial

The effect of nonlinear properties of a material with a periodic structural cell (three-dimensional spiral) on the specificity of transmission and reflection of elliptically polarized laser pulses normally incident on the metamaterial is studied using the finite-difference time-domain method. An analysis of the hodograph of electric-field strength vector showed that an increase in the peak intensity of a linearly polarized laser pulse incident on a sample leads to an increase in the orthogonal component of the electric-field strength vector in the pulse transmitted through the medium. When pulses containing few electric-field periods are incident on a metamaterial, the latter demonstrates radically different optical properties for right- and left-handed circularly polarized light passing through the medium. It was shown that an increase in the intensity of a right-handed (left-handed) circularly polarized ultrashort pulse, incident on a sample composed of a rather large number of right-handed (left-handed) spirals made of nonlinearmaterial, widens the frequency range within which the incident light is almost entirely reflected from the medium.     

Nearly constant loss effect in sodium borate and silver meta-phosphate glasses: New insights

We present new insights into the Nearly Constant Loss (NCL) effect, which are based on a study of conductivity as a function of temperature and frequency in 0.3Na₂O · 0.7B₂O₃ and 0.5AgI · 0.5AgPO₃ glasses. In these systems, the ionic conductivity has been measured over a temperature range from 4 K to 475 K and in a frequency range from a few mHz to a few MHz. The conductivity spectra taken at various temperatures have then been mapped on to a representation of conductivity versus temperature (or inverse temperature) at fixed frequency. Indeed, such plots are often published in studies of the NCL effect. For a given system and a given frequency, an equivalent mapping is achieved by using suitable scaled model conductivity spectra derived from the MIGRATION concept. This enables us to identify, at fixed frequency, the temperature of transition from the ionic conductivity caused by the “ordinary” correlated hopping motion of the mobile ions (now known as the “first” universality) to the classical NCL behaviour (which Nowick termed “new” or “second” universality). We describe the details of our procedure and show that insights emerge with regard to both the high-frequency plateau of the conductivity component due to “ordinary” hopping and the NCL effect itself.     

Highly efficient magnetically tunable high frequency spur-line notch filter

We report a cobalt ferrite nanorods (CFO NRs) based magnetically tunable spur-line notch filter where vertically aligned CFO NRs has been grown on silver nanoparticles coated silicon substrate. The CFO NRs are coupled with high frequency spur-line bandstop filter in flip-chip configuration and the device showed excellent tunable microwave properties in the presence of a low bias magnetic field. The center frequency of the tunable filter is ~16.4 GHz which is shifted to ~14.9 GHz with ~8.7% tunability by applying bias magnetic field ~320 Oe. The magnetic field tuning of the center frequency is explained on the basis of the change in permeability value of the CFO NRs with bias magnetic field as the NRs are used in the partially magnetized state. For validation, permeability value is also calculated by using numerical equations. The experimental reflection of the device has been supported with a simulation using CST microwave studio software.     

Structure and optical properties of carbon films obtained by multipulse pulsed laser deposition

We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm². We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films.     

Limited volume thin film deposition on geometrically complicated substrates

In this paper we report a study on the elastic scattering of electrons by lithium and sodium atoms in the presence of circularly polarized resonant laser field within the framework of the two-state rotating wave approximation. The effect of laser on projectile electrons is described by Volkov states. The frequency of the laser field is chosen to match with the 2s–3p (3s–3p) transition frequency in lithium (sodium) atoms. The total and differential elastic cross sections with single photon exchange are calculated for intermediate energies (50–150 eV) and laser intensity (10⁷–10¹¹ W cm^-2). An erratum to this article can be found online at http://dx.doi.org/. An erratum to this article can be found at     

Second harmonic generation of a self-focused Hermite-Gaussian laser in plasma

Second harmonic generation (SHG) using intense Hermite-Gaussian laser beam (HGLB) propagating through the plasma for mode-indices m = 0 and m = 1 is reported in the present work. Ponderomotive force induced density perturbation beats with the oscillatory velocity of electrons at incident laser frequency, generate the second harmonic nonlinear current that give rise to SHG. Using paraxial approximations, we have derived the coupled equations for the beam width parameter of HGLB and second harmonic's normalized amplitude. Resonance condition is obtained by considering wiggler magnetic field which providing an extra momentum to the second harmonic photon and this result a significant increase in the amplitude of SHG. Our analysis shows the prominent rise in normalized amplitude of second harmonic on increasing the value of the intensity of fundamental laser pulse, normalized wiggler magnetic field and normalized density of plasma. It is notified that the gain of SHG is more prominent for m = 1. Dependency of laser and plasma parameters on SHG is also reported in the current work.     

Centrifugal electron-ion recombination

Transient electric-field pulses have been used to stimulate electron/ion recombination in a low density plasma in the presence of a static electric field. The measured recombination rates exhibit a strong dependence on the relative orientation of the pulsed and static fields. For weak pulses, the recombination rate is significantly higher for orthogonal as opposed to parallel or antiparallel field configurations. The enhanced recombination rate is attributed to the dynamic stabilization of high-m Rydberg levels that are populated during the pulse. Classical simulations confirm the importance of angular momentum rather than energy transfer.     

Realization of an advanced nozzle concept for compact chemical oxygen iodine laser

Conventional supersonic chemical oxygen–iodine lasers (SCOIL) are not only low-pressure systems, with cavity pressure of 2–3 Torr and Mach number of approximately 1.5, but also are high-throughput systems with a typical laser power per unit evacuation capacity of nearly 1 J/l, thus demanding high capacity vacuum systems which mainly determine the compactness of the system. These conventional nozzle-based systems usually require a minimum of a two-stage ejector system for realization of atmospheric pressure recovery in a SCOIL. Typically for a 500 W class SCOIL, a first stage requires a motive gas flow (air) of 120 gm/s to entrain a laser gas flow of 3 g/s and is capable of achieving the pressure recovery in the range of 60–80 Torr. On the other hand, the second stage ejector requires 4.5 kg/s of motive gas (air) to achieve atmospheric pressure recovery. An advanced nozzle, also known as ejector nozzle, suitable for a 500 W-class SCOIL employing an active medium flow of nearly 12 g/s, has been developed and used instead of a conventional slit nozzle. The nozzle has been tested in both cold as well as hot run conditions of SCOIL, achieving a typical cavity pressure of nearly 10 Torr, stagnation pressure of approximately 85 Torr and a cavity Mach number of 2.5. The present study details the gas dynamic aspects of this ejector nozzle and highlights its potential as a SCOIL pressure recovery device. This nozzle in conjunction with a diffuser is capable of achieving pressure recovery equivalent to a more cumbersome first stage of the pressure recovery system used in the case of a conventional slit nozzle-based system. Thus, use of this nozzle in place of a conventional slit nozzle can achieve atmospheric discharge using a single stage ejector system, thereby making the pressure recovery system quite compact.     

干涉型光纤水听器调制光源的一种实现方法

直接调制光源(多量子阱激光器)的相位载波零差检测方式，在干涉型光纤水听器的信号检测技术中具有明显的优越性。详细描述了采用高频正弦波，对多量子阱分布反馈激光器进行直接驱动调制的一种实现方法。实验表明达到了水听器对光源高频稳定的要求。该调制技术也可应用于光纤通信等领域。     

An experimental investigation of inhomogeneities in resonant infrared matrix-assisted pulsed-laser deposited thin polymer films

Thin polymer films are deposited using matrix-assisted pulsed-laser evaporation and subsequently are characterized by scanning electron and atomic force microscopies. An Er : YAG laser (2937 nm, 350 μs) is used as a light source and the effect of the energy density supplied by the laser on the morphology of the deposited films is investigated. It is found that the appearance of undesirable non-uniform morphological features arises from either poor solubility of the guest molecules or insufficient energy density provided by the laser to vaporize the entire ejected volume. In addition, the surface roughness of two guest–host systems is found to depend linearly on the polymer concentration. These results allow us to better understand earlier work in the field and to establish a framework by which MAPLE films may be improved.