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International audience; Control over spin transport in antiferromagnetic systems is essential for future spintronic applications with operational speeds extending to ultrafast time scales. Here, we study the transition from the gigahertz (GHz) to terahertz (THz) regime of spin transport and spin-to-charge current conversion (S2C) in the prototypical antiferromagnet IrMn by employing spin pumping and THz spectroscopy techniques. We reveal a factor of 4 shorter characteristic propagation lengths of the spin current at THz frequencies (~ 0.5 nm) as compared to the GHz regime (~ 2 nm) which may be attributed to the ballistic and diffusive nature of electronic spin transport, respectively. The conclusion is supported by an extraction of sub-picosecond temporal dynamics of the THz spin current. We also report on a significant impact of the S2C originating from the IrMn/non-magnetic metal interface which is much more pronounced in the THz regime and opens the door for optimization of the spin control at ultrafast time scales.

Because of commercial availability in urban areas the market share of wood briquettes is increasing steadily. In 2009 nearly 350.000 to of wood briquettes were sold on the German market [1]. In Austria the amount of sold briquettes increased by 34 % from 2012 to 2013 [2]. Briquettes are predominantly used in conventional log wood stoves. The consequences can be higher emissions and lower efficiency than possible with briquettes. The characteristics of briquettes (geometry, homogeneous fuel composition, etc.) are similar to wood pellets. They therefore offer (semi)automatic combustion which has a high potential to reduce negative influences on emissions and efficiency caused by user behavior or fuel quality. In the COMET-project FOWS II a small scale combustion system which is adapted for characteristics and combustion behavior of briquettes was developed. The innovative small scale combustion system allows the combustion of a vertical briquette which burns like a candle from top to bottom while permanently being hold at the same position in the combustion chamber by a mechanism., Proceedings of the 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp. 1778-1781

Fabrication, spectroscopic properties, and laser performance of a Yb:SiO2 multicomponent glass have been investigated in this paper. The glass system composed of SiO2, Al2O3, and La2O3 excels in terms of a high thermal stress resistance compared to other laser glasses. The laser experiments were conducted with a 3.4 mm thick and 0.9 mol. % Y2O3 doped sample. A maximum slope efficiency of 51%, a maximum optical to optical efficiency of 42%, and a tuning range from 1010–1090 nm was realized. Due to the promising laser properties and a straightforward fabrication technique it may well qualify as an alternative gain medium in high-energy, ultrashort pulse laser systems.

International audience

We successfully demonstrated cw lasing of ytterbium-doped silica multicomponent glass bulk material. A slope efficiency of 43% and a tuning range from 1010-1080 nm have been achieved.

26th European Photovoltaic Solar Energy Conference and Exhibition; 3735-3738, EMC emission measurements on photovoltaic inverters are carried out according to the generic standard IEC61000-6-3. Since edition 2.0 published in 2006, changes have been made in the test setup for conducted radiofrequency measurements. The DC-side of the inverter shall be connected with a CISPR AC-Line Impedance Stabilization Network (LISN). In the first edition, a 150 Ohm LISN according to IEC50022 has been prescribed. Many AC-LISN available on the EMC market include large earth capacities between the lines and PE. For many transformerless inverters, these large capacities in the range of several microfarads will lead to malfunctions or saturation effects in the EMC filters which will never occur if the inverter is connected to a photovoltaic generator whose earth capacity is orders of magnitude lower. Because of these facts, an EMC test according to the actual edition of EN 61000-6-3 on transformerless photovoltaic Inverters is not possible anymore. This disadvantage of the standardization has been discovered in 2007 by Fraunhofer IWES. The investigation results have been discussed with members of national and international standardization organizations. As an overcoming of this disadvantage, a new test setup and a special PV-LISN will be included in the next edition of CISPR11/IEC55011.

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24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 3660-3663, A new measurement technology for automated long term measurement evaluations of photovoltaic (PV) modules has been invented by IWES. The measuring card ISET-mpp meter (Figure 1) not only allows the measurement of the main module parameters but also enables the complete I-V characteristics of the modules to be measured. Especially for newly developed modules this approach offers great potential for performance-tests, derivation of model parameters and new model equations. By using standardized communication commands it is possible to include the measuring board in a data acquisition system. Thus long-term measurements of PV modules in different operating modes and in different environments become possible. The I-V curves of the modules can be determined at specified intervals, or initiated by a trigger signal. Hereby for example, the influence of various weather conditions and shadowing situations to the module performance can be assessed. The measurement results can be sent via a serial port to a PC for further data processing.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 3695-3698, Every PV inverter and electricity meter available on the market is tested according to the standards which are valid for the individual product. Nevertheless, malfunctions of some electronic electricity meters have been detected, when used in conjunction with special PV inverters. In one case, the meter displayed only 85% of the real energy fed into the public grid by the PV inverter [1]. The meter was checked in a calibration laboratory without negative results. Investigations by ISET have shown that the RF ripple current of the inverter influenced the meter. In most inverters, the frequency of the ripple current lies between 3 kHz and 150 kHz. Unfortunately, no emission and immunity requirements exist for inverters and meters within this frequency range [2] [3] [4]. ISET/IWES has developed a special test setup, which can simulate electric ripple currents, similar to those generated by inverters. Investigations on inverter EMC test setups with low differential mode impedance AC artificial mains networks (AMN) are in progress.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 3107-3111, For the quality assurance of photovoltaic inverters, different test procedures must be applied. These are partly defined in standards; however there are partially large uncertainties with application of these procedures, since the photovoltaic specific characteristics in some standards were considered so far only insufficiently. This leads to the problem, that results which are based on these procedures can not be compared with each another. On the other hand, many aspects of the human and system safety as well as the technical function and reliability are normative not regulated! The goal of the project OPTINOS is, to point out and eliminate these deficits by specifying and improving the technical, organizational and normative demands. Thus the project supports the demands of the industry to create uniform test procedures for photovoltaic inverters. The work takes place in coordination with the responsible committees of the DKE. Cooperation with CENELEC and IEC is planned. This paper shows main work items of the project and describes actual research results.

Stresses developing in a planar waveguide resulting from the different thermal expansion coefficients of the substrate and the three glass layers (buffer, core and cladding) were analyzed using a finite element method. It can be shown that mainly the thermal expansion of the overcladding determines the birefringence in the finished waveguide. Based on that result, recipes for an overcladding made with the flame-hydrolysis-deposition-(FHD)-process were devised. We demonstrate the absence of birefringence in a commercial waveguide layer overclad with this glass. The high doping levels required for the cladding to have a thermal expansion coefficient sufficient for this raises concerns about the moisture sensitivity of such a glass. We examined the depth dependent composition of the glass using WD-ESCA (wavelength dispersive electron microprobe) and show, that at the surface a layer depleted of dopants is formed during the higth temperature sintering process. This layer can serve as a protective coating to isolate the underlying, higher doped layer from the effects of moisture. Analysis of the stresses shows that this does not effect the birefringence behavior of the waveguide.