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After more than 3 years of operational experiences with the Transportable Adaptive Optical Ground Station (T-AOGS) it is not any more the question whether optical communication through atmosphere is possible for Geo to ground applications. It is important to understand the performance of optical communication under different atmospheric-conditions and which the key parameters are to improve simplicity, robustness and availability of optical bi-directional satellite to ground links (SGL). We report within this paper on the characterization of the atmospheric channel for ground to GEO optical communication without adaptive optics correction in the uplink. Besides the telemetry data of the space segment and the T-AOGS, also a special measurement campaign was carried out using the 1m telescope of the ESA-OGS in parallel. An outlook for further analysis and activities is given.

Laser Communication Links in Orbit have become routine for Alphasat TDP1 GEO data relay and Sentinel-1A LEO satellite. Since November 2014, an extensive campaign has demonstrated stable and bit-error free links over distances of up to 45.000km with 1.1W optical transmit power and data rates of up to 1.8Gbps. Link acquisition is achieved reliably within less than 55s. Links with low grazing altitude investigate the impact of atmosphere to link performance. The optical links between Sentinel-1A and Alphasat are in collaboration of ESA, DLR, and TESAT Spacecom. Alphasat TDP1 is the precursor for European Data Relay Satellite System EDRS [1].

The microwave-assisted magnetization reversal is modeled in a permalloy micron-sized magnetic ellipsoid. Our simulations confirm that this process requires less field than magnetization reversal under a static field. This is due to a different reversal mode which in the case of the microwave-assisted process is always a ripple structure. During the magnetization reversal, two stages, nucleation and relaxation, are distinguished. The nucleation process is governed by spin-wave instabilities. The relaxation process is related to the domain expansion through domain-wall propagation determined by the precessional motion of magnetic moments in the center of the domain walls. As a consequence, the switching time is a complex oscillating function of the microwave frequency.

In this study quasi-static switching behavior of a Ni81Fe19 ellipsoid (long axis 160mum, short axis 80mum, thickness 10 nm) under the influence of a microwave field by longitudinal magneto-optic Kerr effect magnetometry. The external quasi-static magnetic field is applied parallel to the long axis of the ellipsoid. The uniaxial anisotropy induced during the growth process is also orientated parallel to the long axis of the ellipsoid. The switching behavior of the Ni81Fe19 element is studied by measuring hysteresis curves with an applied microwave field perpendicular to the quasi-static magnetic field. The frequency of the microwave field was varied in the range of 500 MHz to 2.0 GHz in steps of 100 MHz. The microwave power is increased from 3.2 mW to 3.2 W for each frequency, which can be estimated as a field range from 0.2 Oe (3.2 mW) to 7.3 Oe (3.2 W). A strong reduction of the coercive field from 4 Oe to 0.5 Oe is observed in the microwave field range from 2.9 Oe (501.2 mW) to 7.3 Oe (3.2 W) for microwave frequencies between 700 MHz and 900 MHz.

We study microwave assisted magnetization reversal of elliptical Ni81Fe19 thin film elements employing Kerr microscopy. A microwave field is applied along the short axis of the element and orthogonally to a quasistatic magnetic field, which is parallel to the long axis of the element. The reversal process is characterized by the formation of a complex multidomain structure. We demonstrate that the reversal process in total is compressed by applying a sufficiently high microwave field, which assists to overcome the effective energy barrier of the domain nucleation, and thus reduces the coercive field.

The authors demonstrate the stimulation of the magnetization switching process of a Ni81Fe19 ellipsoid, which is dominated by domain nucleation and propagation, by applying a transverse microwave field. The study of the quasistatic switching behavior under the influence of a microwave field was performed using longitudinal magneto-optic Kerr effect magnetometry. A strong reduction of the coercive field for microwave frequencies between 500 and 900MHz has been observed, which can be attributed to two different mechanisms: microwave stimulated enhancement of domain nucleation and microwave stimulated growth of the reversed domain. The authors prove that heating is not the origin of the reduction of the coercive field.

A crossed coplanar waveguide design using polymer insulation layers is developed as a tool to experimentally investigate fast, precessional switching phenomena in view of applications in magnetic random access memory. The photosensitive polymer Cyclotene 4024™ (benzocyclobutene) is used as an electric insulation layer to realize a multilayer sample consisting of several different conducting and insulating layers. We report on the processing of Cyclotene 4024™ multilayers with optimized surface and electric insulating properties after hard cure. The micropatterned impedance matched coplanar waveguides have a bandwidth of 8.5GHz according to −2dB criterion, and for the −3dB criterion the bandwidth exceeds the measurement range of up to 15GHz. These values allow for short rise and fall times of the pulse for ultrafast magnetization dynamics measurements.

A writing scheme is presented for Savtchenko-type magnetic random access memory (MRAM) cells, which allows for ultrafast direct writing with high stability against half select switching, using two orthogonally oriented unipolar magnetic field pulses with time delay, which allows for backswitching by reversing the temporal sequence of the two pulses. The numerical simulations are based on the Stoner–Wohlfarth model and a Runge Kutta integration of the Landau–Lifshitz and Gilbert equation.