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Metrology dedicated to electricity and magnetism has changed considerably in recent years. It encompasses almost all modern scientific, industrial, and societal challenges, e.g. the revision of the International System of Units, the profound transformation of industry, changes in energy use and generation, health, and environment, as well as nanotechnologies (including graphene and 2D materials) and quantum engineering. Over the same period, driven by the globalization of worldwide trade, the Mutual Recognition Arrangement (referred to as the CIPM MRA) was set up. As a result, the regional metrology organizations (RMOs) of national metrology institutes have grown in significance. EURAMET is the European RMO and has been very prominent in developing a strategic research agenda (SRA) and has established a comprehensive research programme. This paper reviews the highlights of EURAMET in electrical metrology within the European Metrology Research Programme and its main contributions to the CIPM MRA. In 2012 EURAMET undertook an extensive roadmapping exercise for proposed activities for the next decade which will also be discussed in this paper. This work has resulted in a new SRA of the second largest European funding programme: European Metrology Programme for Innovation and Research.

There have been controversial reports about the type of magnetic coupling and hence ferromagnetism in ZnMnO. We have investigated the magnetic properties of ZnxMn1−xO layers grown by Molecular Beam Epitaxy (MBE) on sapphire substrates. At first sight, the investigated ferromagnetism in our ZnMnO layers deposited on Al2O3 substrates seemed trivial, but the results of extensive analyses of the layers and also data from the Al2O3 substrates used strongly indicate that the influence of the substrate on magnetic property measurements needs to be considered when confirming ferromagnetism in Mn-doped ZnO layers. Our ZnMnO layers showed a paramagnetic behaviour.

Induced transmittance is observed with polycarbonate laser filters when they are irradiated by laser pulses with a width of 200 fs. These results are compared with measurements in the nanosecond time domain. Calculations by a simple absorption model show, that single photon absorption is dominating the light-matter interaction at the pulse widths used in this study, at least at radiant exposure levels at which the filter material is not damaged. The use of eyewear showing induced transmittance can lead to a risk for the user, if the filter is irradiated by a strong laser beam in an accident. This situation can be even worse when an additional temperature effect is taken into account, which shifts the transmittance characteristics to lower optical densities when the temperature of the laser filter is maintained at a lower level. An example for this effect is given for nanosecond-pulse laser interactions.

We demonstrate an optical limiter for ultra-short (∼100-fs) laser pulses. The device has a dynamic range (= damage energy/onset-of-limiting energy) of more than 10000 and an onset-of-limiting energy of only ∼10 nJ. The output-pulse energy is kept below 1.3 μJ. The limiting mechanism is based on two-photon absorption and refractive nonlinearities in a 20-mm piece of ZnSe. We discuss the importance of the different nonlinearities, damage issues, and guidelines for the construction of the device.

We investigate the nonlinear optical properties of low-temperature-grown (LT) GaAs. It is shown that the strength of the absorptive nonlinearity is weak in as-grown undoped LT-GaAs with a fast recovery time of the nonlinear absorption. The reason for this behavior is revealed by a quantitative study of the nonlinear optical properties of the most important defect transition from the neutral As antisite to the conduction band. Based on this analysis, we demonstrate two methods for the improvement of the ultrafast nonlinearity of LT-grown semiconductors: post-growth annealing or Be doping of LT-GaAs yields a material with a strong ultrafast nonlinear optical response.

We present a combined atomic force microscopy (AFM) and magnetic force microscopy (MFM) study of bacterial magnetosomes, consisting of membrane-covered magnetite particles. AFM imaging unambiguously demonstrates the existence of single isolated magnetosomes with a size of about 40 nm, in addition to various clusters of magnetosomes. With MFM we have particularly addressed the magnetic properties of single magnetosomes. These nanoparticles behave like single mono-domain nanomagnets, as shown by the comparison of the MFM data to simple simulations. These simulations also provide information on the size of the magnetic kernel of the magnetosomes. Moreover, the invasiveness of the MFM tip is addressed.

We investigate the ultrashort coherent dynamics of one-dimensional Fano andvLorentzian magnetoexcitons in GaAs using temporally and spectrally resolved four-wave mixing (FWM). The dephasing time of a Fano resonance is intrinsically limited by the coupling between discrete states and continua which is responsible for Fano interference. In contrast, the coherent emission from Lorentzian magnetoexcitons dephases solely due to quasi-particle scattering, dominated by exciton-exciton scattering at low temperatures. We find a very fast decay of the time-integrated FWM signal from Fano magnetoexciton resonances. This decay is not due to dephasing. The quenching of the FWM signal for non-overlapping excitation pulses is the result of quantum interference. This destructive quantum interference is not observed for purely Lorentzian dynamics. For the simultaneous excitation of Lorentzian and Fano magnetoexciton resonances, destructive quantum interference also quenches the coherent emission from Lorentzian magnetoexcitons due to quantum mechanical coupling between the different resonances.

Using transient four-wave mixing spectroscopy, we study the ultrafast nonlinear optical response of magnetoexcitons in GaAs at 1.6 K. By spectrally and temporally resolving the coherent emission, we measure the magnetic field dependence of Coulomb interactions between magnetoexcitons. Contrary to experiments performed in quantum wells, these interactions persist for field strengths up to 10 T.

The dynamics of optical excitations in a PPP-type ladder polymer have been investigated by means of femtosecond pump-probe experiments. Stimulated emission (SE) is observed around the S 1 → S 0 transition while photoinduced absorption (PA) dominates the differential transmission at lower energies. The stimulated emission is due to singlet exciton recombination. Comparative studies of the temporal behaviour of the SE and the PA demonstrate that the SE and the PA signals originate from different species. Our results provide evidence that the PA is due to spatially separated electron-hole pairs (indirect excitons).

We study the dynamics of coherent emission of a semiconductor within the framework of the semiconductor Bloch equations, both in the time domain and in real space for various excitation conditions. We find that the spatial properties of the four-wave-mixing (FWM) response reflect the well-known temporal dynamics. For excitation high above the band edge, the FWM signal is emitted as a photon echo. This photon echo from continuum states of a semiconductor has the same dynamical properties as a photon echo from inhomogeneously broadened uncoupled two-level systems. However, unlike the case of two-level atoms, the polarization of the photon echo from the semiconductor continuum extends over macroscopic distances in real space. The implications of the large spatial extent of the photon echo polarization are discussed. In particular, we show that, in spite of the macroscopic size of the photon echo polarization, the wavelength of the exciting light can still be neglected.

We study the dynamics of optical excitations in solid films of ladder-type poly(para-phenylene) (LPPP). A low-energy emission band is observed in the photoluminescence spectrum of solid films of this π-conjugated polymer, which is absent in LPPP solutions. We show that the low-energy luminescence can be attributed to aggregates between subunits of the polymer chains. Energy transfer into aggregate states strongly affects the dynamics of excitations in solid LPPP. We further discuss the influence of non-radiative defects on the dynamics.

The coherent dynamics of Fano resonances in GaAs are studied under magnetic field using femtosecond four-wave mixing (FWM). In this system Coulomb coupling between magnetoexciton and continuum states gives rise to Fano interference. By time-resolving the FWM signal it is shown that dephasing or the coherent emission from a Fano resonance is dominated by the coupling to the continuum. Unlike Lorentzian resonances, the decay of the time-integrated FWM signal is not related to dephasing. This surprising behavior is due to the interplay between Fano interference and Coulomb correlation in a semiconductor

We present the first investigation of the ultrafast dynamics of the coherent emission from Fano resonances in semiconductors. Time-resolved femtosecond four-wave mixing (FWM) in GaAs under high magnetic field shows that dephasing is dominated by the coupling between discrete states and continua responsible for the Fano interference. In striking contrast to atomic systems and Lorentzian excitations in semiconductors, the decay of the time-integrated FWM signal is not related to dephasing. This decay is due to quantum interference originating from the interplay between semiconductor many-body effects and Fano interference.

We have observed Fano resonances in linear absorption experiments on GaAs under a magnetic field. In a bulk semiconductor in a magnetic field, Fano interference is the result of the coupling of higher-order magnetoexcitons and energetically degenerate one-dimensional continuum states. We show that these experimental findings can be described by the model of a two-band semiconductor in the effective-mass approximation. Numerical calculations of the linear magnetoabsorption are presented that demonstrate that the coupling between magnetoexcitons and continuum states is due to Coulomb interaction.

Time-resolved demonstration of picosecond photon echoes due to intrinsic optical excitations of a semiconductor is presented. Phase relaxation times up to several hundred picoseconds are found for excitons localized by chemical disorder in ${\mathrm{CdS}}_{\mathrm{x}}$${\mathrm{Se}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ mixed crystals. These long dephasing times are attributed to reduced scattering of the localized excitons as compared to free excitons. Dephasing is identified as due to energy relaxation of the excitons.

We report on the optical properties of tris-(stilbene)amine (TSA) and its application as a light-emitting layer in a microcavity. Time-resolved photoluminescence spectroscopy on a blend of TSA in polycarbonate (PC) demonstrates that the dynamics of the optical excitations significantly depend on the detection energy and temperature. This behaviour is characteristic for hopping relaxation within an inhomogeneously broadened density of states. We have realized a microcavity based on TSA where the emission shows spectral narrowing, intensity enhancement and a change of the radiative lifetime at the wavelength resonant to the cavity mode.

Summary form only given. We present the first practical optical limiter for ultrashort, /spl sim/100 fs, laser pulses. Optical limiters show decreased transmittance with increasing laser pulse energy so that the transmitted energy is kept small. These devices are characterized by the onset-of-limiting energy E/sub on/ (pulse energy at which the transmittance T has fallen to T/sub lin//2, T/sub lin/ transmittance in the linear regime), the "dynamic range" = E/sub D//E/sub on/ (E/sub D/ damage energy), and the maximum transmitted output energy E/sub max/. A practical device for the protection of the human eye or sensitive photodetectors combines a low E/sub on/ with a high dynamic range, small E/sub max/, and a large linear transmittance. With our concept, a low threshold E/sub on/ = 11 nJ, a large dynamic range of 10750, and sufficient linear transmittance T/sub lin/ = 28% are obtained. Moreover, the transmitted energy E/sub max/ is restricted to 1.3 /spl mu/J. Our concept builds on two-photon absorption (TPA) and refractive index effects in ZnSe.

We have quantitatively studied the optical nonlinearity in annealed and in beryllium doped low-temperature grown (LT) GaAs. This study has been complemented by measurements of the temporal decay of the absorption modulation on the 20-fs time scale. Our results show that both be doping and annealing of LT GaAs yield a material with superior properties for ultrafast all-optical switching applications.

We present a combined experimental and theoretical study of the spatio-temporal carrier dynamics in photoconductive switches. Experimental photoluminescence patterns demonstrate substantially different electron-hole dynamics across the excitation laser spot. The density dependence of screening combines with the lateral variation of the carrier density to produce the observed effects. These conclusions are also reached from self-consistent calculations of the drift-diffusion equation and Poisson's equation. Moreover, the theoretical studies show that the current density transients substantially vary over the excitation laser spot. Hence, the inhomogeneous current distribution should be taken into account for future switch optimization.

We have investigated optical dephasing in CdSSe mixed crystals by means of time resolved four-wave mixing. Dephasing times of the order of 200 ps are observed for photon energies corresponding to localized exciton transitions. The inhomogeneous nature of these transitions is clearly resolved by the time asymmetry of the four-wave mixing signal.

Using femtosecond four-wave mixing (FWM), we study the coherent dynamics of Lorentzian and Fano magnetoexciton resonances in GaAs. For unperturbed Lorentzian magnetoexcitons, we find that the time-integrated FWM signal decays due to dephasing processes as expected for Lorentzian resonances. The time-integrated FWM signal from a single Fano magnetoexciton resonance, however, decays quasi-instantaneously although the dephasing time of the Fano resonance is much longer than the time resolution of the experiment. This fast decay is the manifestation of destructive quantum interference. Although destructive quantum interference in our system is closely related to the dynamics of Fano resonances, for the simultaneous excitation of Lorentzian and Fano magnetoexciton resonances destructive quantum interference also strongly affects the dynamics of Lorentzian magnetoexcitons due to quantum-mechanical coupling between the two types of resonances.

A bulk semiconductor provides an excellent system for optically studying the ultrafast dynamics of Coulomb correlated magnetoexcitons. The applications of magnetic field to a 3-D system quantizes the energy levels of states with momentum perpendicular to B and, in contradistinction to experiments performed on 2-D quantum well systems, leaves a 1-D continuum of states with momentum parallel to B. The presence of the continuum states has a dramatic influence on both the linear and nonlinear optical properties. Thus, the experiments described blow track the evolution of the semiconductor from a 3-D to a 1-D system and reveal surprising optical properties not observed in the previously reported studies in quantum wells. Using ultrashort pulsed wave mixing spectroscopy, the authors investigate coherent emission from magnetoexcitons in GaAs. By spectrally resolving the emission, they relate the non periodic beat observed temporally to quantum interferences, which they attribute to Coulomb interactions between magnetoexcitons. Contrary to experiments in quantum wells, these interactions persist for fields strengths up to 10T.

The influence of disorder and localization on optical dephasing of excitons in the semiconductor mixed crystals ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As has been investigated by means of time-resolved four-wave mixing and photon echo experiments. A dephasing time of several hundreds of picoseconds is found for resonantly excited localized excitons in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ while the dephasing time in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As amounts to only a few picoseconds. In ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ dephasing results mainly from hopping processes, i.e., exciton-phonon interaction. The contribution of disorder is negligible in terms of phase relaxation in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$. In contrast, in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As elastic disorder scattering yields an essential contribution to the dephasing rate. We present a theoretical model, which treats dephasing of optical excitations in a disordered semiconductor, including the influence of disorder as well as exciton-phonon interaction. On the base of this model, the experimentally observed differences in the dephasing behavior of excitons in ${\mathrm{CdS}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Se}}_{\mathit{x}}$ and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As are related to the microscopic structure of the disorder potential and the mechanism of exciton localization.

Phase relaxation of optical excitations in condensed matter can be studied by coherent four—wave—mixing experiments in the time domain without requiring assumptions on the spectral properties of the material. For inhomogeneously broadened transitions, three laser pulses at times t = 0, t = t21 and t = T with wave vectors k1, k2 and k3, respectively, generate a stimulated photon echo pulse, emitted time—delayed at t = T+t21 in the momentum—matching direction according to k3+k2−k1. As a function of t21 the echo amplitude decays due to scattering events, described by the dephasing time constant T2 [1].

We study the ultrashort dynamics and the dephasing processes of one-dimensional Lorentzian and Fano magnetoexcitons in GaAs, using temporally and spectrally resolved four-wave mixing. The dephasing of the Lorentzian magnetoexcitons is determined by quasi-particle scattering, dominated by exciton – exciton scattering at low temperatures. In contrast, the dephasing time of the Fano magnetoexcitons is intrinsically limited by the Fano coupling to the continuum. Quantum interference is observed if Fano magnetoexcitons contribute to the four-wave mixing signal. This effect is absent in the case of purely Lorentzian dynamics. We show that Lorentzian and Fano magnetoexciton resonances are coupled by Coulomb correlation and discuss the consequences of this coupling.

We have set up a laser system which simultaneously provides synchronized picosecond pulses in the visible and at a wavelength of 1.06 μm with a repetition rate of 76 MHz. The set-up consists of a dye laser synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser and a fiber-grating compressor for the fundamental wavelength of the Nd;YAG laser. Crosscorrelation measurments reveal the time jitter between the two pulse trains to be less than 10 ps. As a first application we have performed non-degenerate transient grating experiments in semiconductors. The non-degenerate technique allows to use excitation energies well above the bandgap energy and to separate non-linear refractive index effects from photoinduced absorption or transmission changes.