Reconfigurable Surface Micropatterns Based on the Magnetic Field-Induced Shape Memory Effect in Magnetoactive Elastomers

A surface relief grating with a period of 30 µm is embossed onto the surface of magnetoactive elastomer (MAE) samples in the presence of a moderate magnetic field of about 180 mT. The grating, which is represented as a set of parallel stripes with two different amplitude reflectivity coefficients, is detected via diffraction of a laser beam in the reflection configuration. Due to the magnetic-field-induced plasticity effect, the grating persists on the MAE surface for at least 90 h if the magnetic field remains present. When the magnetic field is removed, the diffraction efficiency vanishes in a few minutes. The described effect is much more pronounced in MAE samples with larger content of iron filler (80 wt%) than in the samples with lower content of iron filler (70 wt%). A simple theoretical model is proposed to describe the observed dependence of the diffraction efficiency on the applied magnetic field. Possible applications of MAEs as magnetically reconfigurable diffractive optical elements are discussed. It is proposed that the described experimental method can be used as a convenient tool for investigations of the dynamics of magnetically induced plasticity of MAEs on the micrometer scale.

Terahertz time-domain ellipsometry with high precision for the evaluation of GaN crystals with carrier densities up to 1020 cm−3

Gallium nitride (GaN) is one of the most technologically important semiconductors and a fundamental component in many optoelectronic and power devices. Low-resistivity GaN wafers are in demand and actively being developed to improve the performance of vertical GaN power devices necessary for high-voltage and high-frequency applications. For the development of GaN devices, nondestructive characterization of electrical properties particularly for carrier densities in the order of 1019 cm−3 or higher is highly favorable. In this study, we investigated GaN single crystals with different carrier densities of up to 1020 cm−3 using THz time-domain ellipsometry in reflection configuration. The p- and s-polarized THz waves reflected off the GaN samples are measured and then corrected based on the analysis of multiple waveforms measured with a rotating analyzer. We show that performing such analysis leads to a ten times higher precision than by merely measuring the polarization components. As a result, the carrier density and mobility parameters can be unambiguously determined even at high conductivities.

Miocene continental margin growth dominated by deposits from ocean currents – an example from offshore Norway

<p>The earliest Cenozoic evolution of the Mid-Norwegian and Lofoten-Vesterålen continental margin (~65-70<sup>o</sup> N) involved rifting, opening and finally seafloor spreading, initiating the Norwegian-Greenland Sea. These events resulted in large morphological and structural variations along the margin, creating accommodation space in a deep- to shallow-marine setting that allowed for accumulation of the Miocene sediments of the Kai- and Molo formations. The Cenozoic seismic stratigraphic correlation between the wide Mid-Norwegian and the narrow Lofoten-Vesterålen margin is poorly established. We therefore here analyze a large database of seismic data and exploration wellbores to give new insights on the sedimentary processes and paleo-environments during the Miocene evolution of this complex continental margin segment.</p><p>Steeply dipping clinoforms of the Molo Formation testify to a Miocene coastal outbuilding on the eastern part of the northern Mid-Norwegian margin. West of this, elongated sediment accumulations oriented in an along-slope SSW-NNE direction characterize the palaeo-slope. These are up to ~200 km long, between 40 and 110 km wide and up to ~520 m thick. An internal divergent reflection configuration characterize the elongated accumulations and they typically display a progressive upslope onlapping relationship onto an overall gently westward-dipping underlying morphology that includes domes, highs and ridges. Small incisions are frequently observed in association with the upslope onlap. These characteristics are altogether typical of contourites deposited from ocean currents. In the Vøring Basin, the internal seismic configuration can be described as consisting of low to moderate amplitude parallel-layered reflections, which are interpreted to represent a deep-water hemipelagic setting.</p><p>On the much narrower Lofoten-Vesterålen margin, parts of the Kai Formation show a seismic reflection configuration similar to what is observed on the northern Mid-Norwegian margin (e.g. elongated character, divergent internal reflections). These sediments are therefore also interpreted to be contouritic- and hemipelagic deposits. In contrast to the northern Mid-Norwegian contourites, the Lofoten-Vesterålen contourites are generally thinner, and they onlap onto an underlying steeply dipping continental slope, a slope which is also characterized by submarine canyons. Downslope of these, depocenters oriented perpendicular to the margin (i.e. slope-parallel), suggest influence of downslope processes through the canyons.</p><p>Our preliminary results show the presence of several contourite build-ups on the investigated margin, indicating the occurrence of a well-established ocean circulation with a persistent current direction along the Norwegian margin during deposition of the Kai Formation. The main source area for these sediments were likely south of the Mid-Norwegian margin. Coastal outbuilding in the Molo Formation and canyon-fed sediment input also testify to a sediment input from the east in the Miocene, and some of these were likely also re-distributed by ocean currents.</p>

Generation of static and dynamic small calibration forces and their measurements by electromagnetic force compensation balance

The paper presents some of the results of the static and dynamic force measurements at 100 nN to sub-10 µN ranges which are generated due the photon-momentum. The force sensor with resolution about 20 nN and operating in differential measurement mode is developed by two electromagnetic force compensation balances. In order to generate these calibration forces, CW lasers with different operational modes, power levels, and wavelengths are used. Multi-reflection configuration of the laser beam inside the macroscopic cavity with highly reflective mirrors are used to test and variate the total amount of the forces.

Towards Fingerprint Spoofing Detection in the Terahertz Range

Spoofing attacks using imitations of fingerprints of legal users constitute a serious threat. In this study, a terahertz time domain spectroscopy (TDS) setup in a reflection configuration was used for the non-intrusive detection of fingerprint spoofing. Herein, the skin structure of the finger pad is described with a focus on the outermost stratum corneum. We identified and characterized five representative spoofing materials and prepared thin and thick finger imitations. The complex refractive index of the materials was determined in TDS in the transmission configuration. For dataset collection, we selected a group of 16 adults of various ages and genders. The reflection results were analyzed both in the time (reflected signal) and frequency (reflectivity) domains. The measured signals were positively verified with the theoretical calculations. The signals corresponding to samples differ from the finger-related signals, which facilitates spoofing detection. Thanks to deconvolution, we provide a basic explanation of the observed phenomena. We propose two spoofing detection methods, predefined time–frequency features and deep learning based. The methods achieved high true detection rates of 87.9% and 98.8%. Our results show that the terahertz technology can be successfully applied for spoofing detection with high detection probability.

TiOxNy Thin Film Sputtered on a Fiber Ball Lens as Saturable Absorber for Passive Q-Switched Generation of a Single-Tunable/Dual-Wavelength Er-Yb Double Clad Fiber Laser

The use of titanium oxynitride (TiOxNy) thin films as a saturable absorber (SA) element for generation of passive Q-switched (PQS) laser pulses, from a linear cavity Er-Yb double-clad fiber (EYDCF) laser, is demonstrated. Additionally, the deposition of the material as a thin film covering a fiber micro-ball lens (MBL) structure is reported for the first time. The TiOxNy coating is deposited by a direct current (DC) magnetron-sputtering technique. The MBL is inserted within the laser cavity in a reflection configuration, alongside a reflecting mirror. As a result, the coated fiber MBL simultaneously acts as a SA element for PQS laser pulses generation and as an interference filter for wavelength selection and tuning of the generated laser line. Tunable single-laser emission in a wavelength range limited by dual-wavelength laser generation at 1541.96 and 1547.04 nm is obtained. PQS laser pulses with a repetition rate from 18.67 to 124.04 kHz, minimum pulse duration of 3.57 µs, maximum peak power of 0.359 W, and pulse energy of 1.28 µJ were obtained in a pump power range from 1 to 1.712 W.