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- ItemIn situ measurements of optical properties at Tinfou (Morocco) during the Saharan Mineral Dust Experiment SAMUM 2006(Milton Park : Taylor & Francis, 2017) Schladitz, A.; Müller, T.; Kaaden, N.; Massling, A.; Kandler, K.; Ebert, M.; Weinbruch, S.; Deutscher, C.; Wiedensohler, A.In situ measurements of optical and physical properties of mineral dust were performed at the outskirts of the Saharan Desert in the framework of the Saharan Mineral Dust Experiment part 1 (SAMUM-1). Goals of the field study were to achieve information on the extent and composition of the dust particle size distribution and the optical properties of dust at the ground. For the particle number size distribution, measured with a DMPS/APS, a size dependent dynamic shape factor was considered. The mean refractive index of the particles in this field study is 1.53–4.1 × 10-3i at 537 nm wavelength and 1.53–3.1 × 10-3i at 637 nm wavelength derived from measurements of scattering and absorption coefficients, as well as the particle size distribution. Whereas the real part of the refractive index is rather constant, the imaginary part varies depending on the mineral dust concentrations. For high dust concentration the single scattering albedo is primarily influenced by iron oxide and is 0.96 ± 0.02 and 0.98 ± 0.01 at 537 nm and 637 nm wavelength, respectively. During low dust concentration the single scattering albedo is more influenced by a soot-type absorber and is 0.89 ± 0.02 and 0.93 ± 0.01 for the same wavelengths.
- ItemMicrophysical and optical properties of dust and tropical biomass burning aerosol layers in the Cape Verde region - an overview of the airborne in situ and lidar measurements during SAMUM-2(Milton Park : Taylor & Francis, 2017) Weinzierl, Bernadett; Sauer, Daniel; Esselborn, Michael; Petzold, Andreas; Veira, Andreas; Rose, Maximilian; Mund, Susanne; Wirth, Martin; Ansmann, Albert; Tesche, Matthias; Gross, Silke; Freudenthaler, VolkerIn the framework of the Saharan Mineral Dust Experiment (SAMUM) airborne High Spectral Resolution Lidar and in situ measurements of the particle size, aerosol mixing state and absorption coefficient were conducted. Here, the properties of mineral dust and tropical biomass burning layers in the Cape Verde region in January/February 2008 are investigated and compared with the properties of fresh dust observed in May/June 2006 close the Sahara. In the Cape Verde area, we found a complex stratification with dust layers covering the altitude range below 2 km and biomass burning layers aloft. The aerosol type of the individual layers was classified based on depolarization and lidar ratios and, in addition, on in situ measured Ångström exponents of absorption åap. The dust layers had a depth of 1.3 ± 0.4 km and showed a median åap of 3.95. The median effective diameter Deff was 2.5 μm and the dust layers over Cape Verde yielded clear signals of aging: large particles were depleted due to gravitational settling and the accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The tropical biomass layers had a depth of 2.0 ± 1.1 km and were characterized by a median åap of 1.34. They always contained a certain amount of large dust particles and showed a median Deff of 1.1 μm and a fine mode Deff,fine of 0.33. The dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23 and 0.09, respectively. The median contributions to the AOD of the total atmospheric column below 10 km were 75 and 37%, respectively.
- ItemOptical and microphysical properties of smoke over Cape Verde inferred from multiwavelength lidar measurements(Milton Park : Taylor & Francis, 2017) Tesche, Matthias; Müller, Detlef; Gross, Silke; Ansmann, Albert; Althausen, Dietrich; Freudenthaler, Volker; Weinzierl, Bernadett; Veira, Andreas; Petzold, AndreasLidar measurements of mixed dust/smoke plumes over the tropical Atlantic ocean were carried out during the winter campaign of SAMUM-2 at Cape Verde. Profiles of backscatter and extinction coefficients, lidar ratios, and Ångstr¨om exponents related to pure biomass-burning aerosol from southern West Africa were extracted from these observations. Furthermore, these findings were used as input for an inversion algorithm to retrieve microphysical properties of pure smoke. Seven measurement days were found suitable for the procedure of aerosol-type separation and successive inversion of optical data that describe biomass-burning smoke. We inferred high smoke lidar ratios of 87 ± 17 sr at 355 nm and 79 ± 17 sr at 532 nm. Smoke lidar ratios and Ångstr¨om exponents are higher compared to the ones for the dust/smoke mixture. These numbers indicate higher absorption and smaller sizes for pure smoke particles compared to the dust/smoke mixture. Inversion of the smoke data set results in mean effective radii of 0.22 ± 0.08 μm with individual results varying between 0.10 and 0.36 μm. The single-scattering albedo for pure biomass-burning smoke was found to vary between 0.63 and 0.89 with a very low mean value of 0.75 ± 0.07. This is in good agreement with findings of airborne in situ measurements which showed values of 0.77 ± 0.03. Effective radii from the inversion were similar to the ones found for the fine mode of the in situ size distributions.
- ItemHybrid soliton dynamics in liquid-core fibres(Berlin : Nature Pulishing, 2017) Chemnitz, Mario; Gebhardt, Martin; Gaida, Christian; Stutzki, Fabian; Kobelke, Jens; Limpert, Jens; Tünnermann, Andreas; Schmidt, Markus A.The discovery of optical solitons being understood as temporally and spectrally stationary optical states has enabled numerous innovations among which, most notably, supercontinuum light sources have become widely used in both fundamental and applied sciences. Here, we report on experimental evidence for dynamics of hybrid solitons—a new type of solitary wave, which emerges as a result of a strong non-instantaneous nonlinear response in CS2-filled liquid-core optical fibres. Octave-spanning supercontinua in the mid-infrared region are observed when pumping the hybrid waveguide with a 460 fs laser (1.95 μm) in the anomalous dispersion regime at nanojoule-level pulse energies. A detailed numerical analysis well correlated with the experiment uncovers clear indicators of emerging hybrid solitons, revealing their impact on the bandwidth, onset energy and noise characteristics of the supercontinua. Our study highlights liquid-core fibres as a promising platform for fundamental optics and applications towards novel coherent and reconfigurable light sources.
- ItemUniaxial stress flips the natural quantization axis of a quantum dot for integrated quantum photonics(London : Nature Publishing Group, 2018) Yuan, X.; Weyhausen-Brinkmann, F.; Martín-Sánchez, J.; Piredda, G.; Křápek, V.; Huo, Y.; Huang, H.; Schimpf, C.; Schmidt, O.G.; Edlinger, J.; Bester, G.; Trotta, R.; Rastelli, A.The optical selection rules in epitaxial quantum dots are strongly influenced by the orientation of their natural quantization axis, which is usually parallel to the growth direction. This configuration is well suited for vertically emitting devices, but not for planar photonic circuits because of the poorly controlled orientation of the transition dipoles in the growth plane. Here we show that the quantization axis of gallium arsenide dots can be flipped into the growth plane via moderate in-plane uniaxial stress. By using piezoelectric strain-actuators featuring strain amplification, we study the evolution of the selection rules and excitonic fine structure in a regime, in which quantum confinement can be regarded as a perturbation compared to strain in determining the symmetry-properties of the system. The experimental and computational results suggest that uniaxial stress may be the right tool to obtain quantum-light sources with ideally oriented transition dipoles and enhanced oscillator strengths for integrated quantum photonics.
- ItemA comparison of aerosol chemical and optical properties from the 1st and 2nd Aerosol Characterization Experiments(Milton Park : Taylor & Francis, 2016) Quinn, P.K.; Bates, T.S.; Coffman, D.J.; Coffman, Derek J.; Miller, T.L.; Johnson, J.E.; Covert, D.S.; Putaud, J.- P.; Neusüß, C.; Novakov, T.Shipboard measurements of aerosol chemical composition and optical properties were made during both ACE-1 and ACE-2. ACE-1 focused on remote marine aerosol minimally perturbed by continental sources. ACE-2 studied the outflow of European aerosol into the NE Atlantic atmosphere. A variety of air masses were sampled during ACE-2 including Atlantic, polar, Iberian Peninsula, Mediterranean, and Western European. Reported here are mass size distributions of non-sea salt (nss) sulfate, sea salt, and methanesulfonate and submicron and supermicron concentrations of black and organic carbon. Optical parameters include submicron and supermicron aerosol scattering and backscattering coefficients at 550 nm, the absorption coefficient at 550±20 nm, the Ångström exponent for the 550 and 700 nm wavelength pair, and single scattering albedo at 550 nm. All data are reported at the measurement relative humidity of 55%. Measured concentrations of nss sulfate aerosol indicate that, relative to ACE-1, ACE-2 aerosol during both marine and continental flow was impacted by continental sources. Thus, while sea salt controlled the aerosol chemical composition and optical properties of both the submicron and supermicron aerosol during ACE-1, it played a relatively smaller role in ACE-2. This is confirmed by the larger average Ångström exponent for ACE-2 continental aerosol of 1.2±0.26 compared to the ACE-1 average of -0.03±0.38. The depletion of chloride from sea salt aerosol in ACE-2 continental air masses averaged 55±25% over all particle sizes. This compares to the ACE-2 marine average of 4.8±18% and indicates the enhanced interaction of anthropogenic acids with sea salt as continental air masses are transported into the marine atmosphere. Single scattering albedos averaged 0.95±0.03 for ACE-2 continental air masses. Averages for ACE-2 and ACE-1 marine air masses were 0.98±0.01 and 0.99±0.01, respectively.
- ItemAttosecond time-resolved photoelectron holography([London] : Nature Publishing Group UK, 2018) Porat, G.; Alon, G.; Rozen, S.; Pedatzur, O.; Krüger, M.; Azoury, D.; Natan, A.; Orenstein, G.; Bruner, B.D.; Vrakking, M. J.J.; Dudovich, N.Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography - all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds.
- ItemHighly-efficient extraction of entangled photons from quantum dots using a broadband optical antenna(London : Nature Publishing Group, 2018) Chen, Y.; Zopf, M.; Keil, R.; Ding, F.; Schmidt, O.G.Many quantum photonic technologies require the efficient generation of entangled pairs of photons, but to date there have been few ways to produce them reliably. Sources based on parametric down conversion operate at very low efficiency per pulse due to the probabilistic generation process. Semiconductor quantum dots can emit single pairs of entangled photons deterministically but they fall short due to the extremely low-extraction efficiency. Strategies for extracting single photons from quantum dots, such as embedding them in narrowband optical cavities, are difficult to translate to entangled photons. Here, we build a broadband optical antenna with an extraction efficiency of 65% ± 4% and demonstrate a highly-efficient entangled-photon source by collecting strongly entangled photons (fidelity of 0.9) at a pair efficiency of 0.372 ± 0.002 per pulse. The high brightness achieved by our source represents a step forward in the development of optical quantum technologies.