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Waveplates, used to modify polarization state of light, are integral part of high-power lasers. Classical approach to waveplate manufacturing is based on combination of birefringent crystalline materials and deposition of nonpolarizing antireflection (AR) coatings. Their limitation to withstand maximal peak power is determined by laser-induced damage (LID) phenomena, mainly determined by low band-gap materials used in AR coatings. In this study, a novel multi-layer approach of high band-gap birefringent coatings was proposed and investigated to overcome this limitation. Three eligible candidate materials, namely LaF3, Al2O3, and SiO2 are investigated. Structural and optical analysis reveal superior properties of silica for UV spectral range. Zero-order thin film retarders based on all-silica nano-structures are fabricated by oblique angle deposition process. Low optical losses and high transparency ( T ∼ 99%) are demonstrated while indicating potential to withstand high laser fluence of 40 J cm−2 in nanosecond regime at 355 nm wavelength. Such waveplates can essentially improve maximal tolerated peak power and thus allow production of more compact optical systems, even when high laser power is used. [ABSTRACT FROM AUTHOR]

ABSTRACT The advances in semiconductor fabrication technologies have enabled the integration of Lamb-wave resonator on silicon substrate. But such integration has led to additional parasitic effects to the Lamb-wave resonators. The availability of an efficient equivalent-circuit model is thus vital. This paper proposes a modified hybrid π-type/Butterworth-Van Dyke (PiBVD) model. Compared with the conventional PiBVD model, the modified PiBVD model accounts for the parasitic inductances of the bonding wires. It therefore provides better accuracy when characterizing Lamb-wave resonators over a wide frequency range. Experiment results have also verified that the modified PiBVD model has better fitting on Y11 (input reflection factor in Y-parameter matrix). This improvement is greatly beneficial for resonator analysis and circuit designs © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:703-706, 2017 [ABSTRACT FROM AUTHOR]

Cointegration has been recently brought to structural health monitoring (SHM) as a new methodology for dealing with the problem of environmental and/or operational variability in monitored structures. However, it is well known that the choice of lag length in cointegration analysis has a strong influence on damage detection results. The article presents a new approach for optimal lag length selection in cointegration analysis used for structural damage detection. This new method is based on stationarity analysis of data representing undamaged condition. The proposed method is validated using Lamb wave data under the effects of temperature variations and vibroacoustic data obtained from nonlinear vibroacoustic modulation experiments with different low-frequency vibration (or modal) excitations. The results demonstrate the effectiveness of the method for structural damage detection based on SHM data heavily affected by environmental or operational conditions. [ABSTRACT FROM AUTHOR]

Optical properties of a metasurface which can be considered a monolayer of uniaxial metamaterials - parallel-plate and nanorod arrays - are investigated. It is shown that such metasurface acts as an ultimately thin sub-100 nm wave plate. This is achieved via an interplay of epsilon-near-zero and epsilon-near-pole behavior along different axes in the plane of the metasurface allowing for extremely rapid phase difference accumulation in very thin metasurface layers. These effects are shown to not be disrupted by non-locality and can be applied to the design of ultrathin wave plates, Pancharatnam-Berry phase optical elements and plasmon-carrying optical torque wrench devices. [ABSTRACT FROM AUTHOR]

A table of contents for the 2016 issue of the journal "Annalen der Physik" is presented.

ABSTRACT A composite panel with a pre-introduced hole was repaired with an external repair patch and tested under tension-tension fatigue. X-ray radiography and microscopic analysis were employed to assess the developed damage which appeared first in the form of axial splitting at the hole and propagation until the final patch debonding. Piezoelectric transducers bonded on the top and bottom of the tested surface were utilised in-phase and out-of-phase in order to excite separately the symmetric and antisymmetric fundamental Lamb wave modes. The estimation of each mode's arrival time was performed through the Akaike information criterion which indicated that only the excitation of the antisymmetric mode was successful due to the possible corruption of the symmetric mode with the shear horizontal mode. The study investigated the problem of inadequate training data set that resulted in a negative Mahalanobis squared distance after outlier analysis application. The study suggested a pseudoinverse approach for the inverse of the covariance matrix and a reduction in the selected feature through the principal component analysis and the isolation of the most representative principal components. Finally outlier analysis was applied, which successfully represented the condition of the structural integrity. [ABSTRACT FROM AUTHOR]

In der hier vorgestellten Arbeit wird die Materialermüdung von Stahlproben anhand der Verzerrung von Lamb-Wellen untersucht. Gekerbte Stahlproben werden zyklisch auf Zug bis zum Bruch im Low-Cycle-Fatigue (LCF) belastet. In Abständen von 1000 Lastzyklen wird die Prüfmaschine angehalten. Ein Aktuator regt Lamb-Wellen bei einzelnen Frequenzen und Frequenzbändern im Bereich von 1 bis 500 kHz an. Nachdem die Lamb-Wellen die Kerbe durchlaufen haben, werden sie von einem Sensor aufgenommen. Die Auswertung der gemessenen Spektren zeigt, dass die mittlere Amplitude mit zunehmender Materialermüdung kleiner wird. Diese Ergebnisse bieten die Grundlage zur Entwicklung eines möglichst robusten Verfahrens zur Risserkennung. Ein wesentlicher Vorteil eines solchen Ansatzes ist, dass kurz vor der Entstehung sichtbarer Risse die Materialermüdung erkannt werden kann, ohne dass dafür Referenzmessungen des ungeschädigten Bauwerks nötig sind. Lamb-wave distortion as approach to detect cracks in steel plates The work presented here examines fatigue of steel specimens based on harmonic-distortion of Lamb-waves. Cyclic tension load is applied on notched steel specimens until failure under Low-Cycle-Fatigue (LCF) occurs. The fatigue test is interrupted every 1000 load cycles. An actuator excites Lamb-waves with singular frequencies and frequency bands in a range from 1 to 500 kHz. After the Lamb-waves passed the notch they are recorded by a sensor. Analysing the spectra shows a declining of the average amplitude with increasing material fatigue. These results provide an approach to develop a robust crack detection methodology. A major advantage of such an approach is the ability to detect cracks at least shortly before they become visible without requiring reference measurements of the undamaged structure. [ABSTRACT FROM AUTHOR]

This paper is devoted to the energy decay estimates for the two‐dimensional coupled wave‐plate system with local frictional damping in a bounded domain. The frictional damping is only distributed in the part of the plate's or wave's domain, and the other is stabilized by the transmission through the interface of the plate's and wave's domains. Using the frequency domain approach and the multiplier technique, we show respectively that the energy of the system decays polynomially under some geometric condition when the frictional damping only acts on the part of the plate, and the energy of the system is exponentially stable when the frictional damping acts only on the other part of the wave. [ABSTRACT FROM AUTHOR]

A temperature‐responsive polarization converter, which reversibly changes from a full‐wave to a half‐wave plate upon heating, is developed. The polymer wave plate has a controlled thickness and is based on a uniaxial aligned nematic semi‐interpenetrating network coating containing a specific concentration of a non‐crosslinked liquid crystal elastomer. Upon heating, the effective birefringence of the wave plate halves without changing the thickness. The function of the wave plate is demonstrated by sandwiching the tunable polarization converter between two identical right‐handed circular polarized light reflective films with a wavelength around 770 nm. At low temperatures, this optical device reflects 50% of light at 770 nm, whereas at elevated temperature 81% is reflected. Such temperature‐responsive optical devices have potential applications for both aesthetic purposes as well as energy saving windows. [ABSTRACT FROM AUTHOR]

The delay‐and‐sum (DaS) methodology is implemented in the current study to depict the probability of damage presence on an aluminum plate. Compared to previous researches, the introduced modification in this work attempts to decrease the dependency of the method on the chosen frequency. Firstly, the propagation of the Lamb waves in the plate is modeled numerically employing commercial finite element package, ABAQUS. Additionally, an experimental setup is built, in which piezo patches are utilized to excite the Lamb wave and to measure the corresponding response on the plate as well. Analysis of the experimental results shows the feasibility of the method for damage detection. [ABSTRACT FROM AUTHOR]

Higher harmonics are sensitive to micro‐defects, which can be utilized in the development of nonlinear ultrasonic techniques (NLUTs). Thus, the higher harmonic generation by material nonlinearity has attracted considerable attention. However, few works have been done on the elastic wave propagation in a finite structure with a localized region of material nonlinearity. The propagation of the SH wave in a plate with a localized region of quadratic material nonlinearity is investigated in this paper. The nonlinear governing equations are reduced to a set of linear equations at different orders by using the perturbation method. The incident plane SH wave satisfies the zero‐order equations. The elastic waves generated by the nonlinear material region can be obtained by solving the first‐order equations, whose inhomogeneous terms can be regarded as the equivalent body forces and surface tractions. In the first‐order approximation, only the Lamb wave can be generated by the interaction of the SH wave with a region of quadratic material nonlinearity. In this paper, the analytical solution for the generated backward Lamb wave is obtained, whose amplitude varies with a material‐dependent constant linearly and with the length of the nonlinear region in the form of a sine function. [ABSTRACT FROM AUTHOR]

The developments of personalized medicine, ultrasound imaging, and contactless "microscopic handle" techniques are pushing ultrasonic transducers toward features of high frequency, device miniaturization, and even novel function. However, the conventional ultrasonic transducer has severely limited the development of novel ideas for applications due to its ordinary ultrasonic field. Although transducer arrays and monolithic acoustic holograms are capable of producing the complicated ultrasonic field, it is still difficult to achieve high frequency, device miniaturization, and novel function simultaneously. Here, a simple but effective approach is introduced that aims at reconstructing the complicated and high‐frequency ultrasonic field via a compact single‐element ultrasonic transducer. The 3D ultrathin piezoelectric element with a complex configuration is demonstrated theoretically and experimentally to produce the desired complicated ultrasonic field. With helical‐like configuration, the single‐element ultrasonic transducer offers efficient noncontact trapping and manipulation of suspended microparticles and biological cells. Moreover, its strong trapping capability leads to the 3D stacking of microparticles, which is a novel and interesting phenomenon achieved by a single‐element ultrasonic transducer. This work brings the possibility of a complicated ultrasonic field for achieving novel high‐frequency ultrasound applications through the design of smart structure ultrathin piezoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract: The results of theoretical and experimental investigation into resonance phenomena accompanying guided wave propagation in a metallic plate with a finite regular system of rectangular deep notches are presented. While the expected intensification of wave blocking by a system of notches comparing to the case of a single defect is confirmed, the resonance transmission at the predicted frequencies within these forming stop bands is also observed. Noticeable motion localization in the waveguide area between the notches at these frequencies is visualized with experimental surface B‐scans. Their patterns coincide with the theoretical predictions obtained on the basis of a semi‐analytical computer model for the notched infinite plate. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Theoretical calculations of the Lamb shift provide the basis required for the determination of the Rydberg constant from spectroscopic measurements in hydrogen. The recent high‐precision determination of the proton charge radius drastically reduces the uncertainty in the hydrogen Lamb shift originating from the proton size. As a result, the dominant theoretical uncertainty now comes from the two‐ and three‐loop QED effects, which calls for further advances in their calculations. The present status of theoretical calculations of the Lamb shift in hydrogen and light hydrogen‐like ions with the nuclear charge number up to Z=5 is reviewed. Theoretical errors due to various effects are critically examined and estimated. [ABSTRACT FROM AUTHOR]

Honeycomb sandwich composites are extensively used in military shelters, aerospace structures, ground transportation structures, auto‐racing bodies, ship panels, and other special purpose structures requiring lightweight construction materials. But debondings at the face‐sheet‐to‐core junctions frequently occur due to the variable operating and loading conditions, which may menace the safety and overall integrity of the structural assembly. This paper aims to effectively identify such hidden debonding regions in these advanced structures, using Lamb wave‐based monitoring technique. A semianalytical analysis of Lamb wave dispersion in a healthy sandwich structure is carried out to identify various Lamb modes and to study their propagation phenomenon. A combined finite element‐based simulation and experimental analysis of Lamb wave propagation in sandwich panels (healthy and with debonding) are then carried out using piezoelectric transducer networks. It is observed that the presence of debonding significantly reduces the propagating Lamb wave mode amplitudes. A debonding detection algorithm, which uses the differential changes in Lamb mode amplitudes, is applied to efficiently identify single and multiple debonding regions in the structure. [ABSTRACT FROM AUTHOR]

No abstract is available for this article. [ABSTRACT FROM AUTHOR]

The adoption of charge-mode amplification, rather than the classical voltage-mode, to interface piezoelectric interdigital transducers made of polymer film to the data acquisition electronics is described. The circuit and operating principles of a charge amplifier are briefly explained, followed by the experimental comparison of a charge amplifier implementation with a solution based on an instrumentation amplifier. The experiments, based on A0-mode Lamb wave transmission over an aluminium plate, demonstrate the effectiveness of chargemode interfacing and its insensitivity to cable loading. [ABSTRACT FROM AUTHOR]

The complex internal structure of modern laminate composite materials, for example, carbon fiber reinforced plastics (CFRP), has a pronounced influence on the propagation of elastic guided waves (GWs). Along with the well‐known anisotropy‐conditioned amplitude and dispersion directivity of source‐induced wavefields and their remarkable attenuation due to the polymer matrix viscosity, continuous mode conversion (CMC) of GWs in multilayered composites fabricated from unidirectional prepregs has been recently observed experimentally. The latter means that the symmetric fundamental mode continuously converts into the antisymmetric one without passing a damage, that is, even in an intact structure. Being strongly related to the inhomogeneous CFRP microstructure and possessing remarkable intensity for specific propagation directions, this phenomenon should be accounted for in ultrasonic nondestructive testing and structural health monitoring systems. In this work, we investigate the CMC phenomenon in an important class of laminates, namely cross‐ply ones, experimentally as well as numerically. In the computational model it is addressed through the concept of spatially varying material properties, and the finite element method (FEM) is employed for the GW propagation simulation. Experimental measurements are performed for piezoelectrically excited GWs with scanning laser Doppler vibrometry technique, allowing clear visualization of the CMC phenomenon and confirming theoretically predicted dependence of its intensity from propagation direction. [ABSTRACT FROM AUTHOR]

Recently, oblique angle deposition has been extensively used to form advanced optical coatings for high power lasers. In present work (article No. 201700764), a novel approach to form multilayer zero‐order all‐silica based waveplates is demonstrated. Study shows the superior optical performance of tested sample and capabilities to withstand high laser fluence of 40 J cm−2 in nanosecond regime at 355 nm wavelength. Such elements can essentially improve compact optical systems, even when high laser power is used. [ABSTRACT FROM AUTHOR]

The presence of magnetic fields in Be stars is highly controversial and still under debate. In this work, we report the results of our search for the presence of a magnetic field and its short-time variability in the well-known non-radially-pulsating single bright Be star λ Eri using several low-resolution spectropolarimetric time series obtained with the ESO FORS 1/2 instruments in 2006, 2007, and, most recently, in 2016. The longitudinal magnetic field for the individual measurements, each using a combination of observations with the quarter-wave plate positions +45° and −45°, oscillates between +470 and −540 G with rather high standard errors of the measurements, up to 200-300 G. Still, a few measurements indicate the presence of a signal at 2.5-4 σ significance. A search for periodicity in the time series from 2006 to 2016 indicates the potential presence of a magnetic variability modulation with a period of ∼13.7 min, which possibly can be taken as a hint for the presence of a small-scale magnetic field on the stellar surface. [ABSTRACT FROM AUTHOR]

A review of the article ``High-power random distributed feedback fiber laser: From science to application'' by Hanwei Zhang, "Ultimately Thin Metasurface Wave Plates" by David Keene and "Large circular dichroism and optical rotation in titanium doped chiral silver nanorods" by Jitto Titus.