Independent tuning of excitonic emission energy and decay time in single semiconductor quantum dots

Independent tuning of emission energy and decay time of neutral excitons confined in single self-assembled In(Ga)As/GaAs quantum dots is achieved by simultaneously employing vertical electric fields and lateral biaxial strain fields. By locking the emission energy via a closed-loop feedback on the piezoelectric actuator used to control the strain in the quantum dot, we continuously decrease the decay time of an exciton from 1.4 to 0.7 ns. Both perturbations are fully electrically controlled and their combination offers a promising route to engineer the indistinguishability of photons emitted from spatially separated single photon sources. © 2017 Author(s)

Independent tuning of excitonic emission energy and decay time in single semiconductor quantum dots

Independent tuning of emission energy and decay time of neutral excitons confined in single self-assembled In(Ga)As/GaAs quantum dots is achieved by simultaneously employing vertical electric fields and lateral biaxial strain fields. By locking the emission energy via a closed-loop feedback on the piezoelectric actuator used to control the strain in the quantum dot, we continuously decrease the decay time of an exciton from 1.4 to 0.7 ns. Both perturbations are fully electrically controlled and their combination offers a promising route to engineer the indistinguishability of photons emitted from spatially separated single photon sources

ALADINA – an unmanned research aircraft for observing vertical and horizontal distributions of ultrafine particles within the atmospheric boundary layer

This paper presents the unmanned research aircraft Carolo P360 "ALADINA" (Application of Light-weight Aircraft for Detecting IN situ Aerosol) for investigating the horizontal and vertical distribution of ultrafine particles in the atmospheric boundary layer (ABL). It has a wingspan of 3.6 m, a maximum take-off weight of 25 kg and is equipped with aerosol instrumentation and meteorological sensors. A first application of the system, together with the unmanned research aircraft MASC (Multi-Purpose Airborne Carrier) of the Eberhard Karls University of Tübingen (EKUT), is described. As small payload for ALADINA, two condensation particle counters (CPC) and one optical particle counter (OPC) were miniaturised by re-arranging the vital parts and composing them in a space-saving way in the front compartment of the airframe. The CPCs are improved concerning the lower detection threshold and the response time to less than 1.3 s. Each system was characterised in the laboratory and calibrated with test aerosols. The CPCs are operated in this study with two different lower detection threshold diameters of 11 and 18 nm. The amount of ultrafine particles, which is an indicator for new particle formation, is derived from the difference in number concentrations of the two CPCs (ΔN). Turbulence and thermodynamic structure of the boundary layer are described by measurements of fast meteorological sensors that are mounted at the aircraft nose. A first demonstration of ALADINA and a feasibility study were conducted in Melpitz near Leipzig, Germany, at the Global Atmosphere Watch (GAW) station of the Leibniz Institute for Tropospheric Research (TROPOS) on 2 days in October 2013. There, various ground-based instruments are installed for long-term atmospheric monitoring. The ground-based infrastructure provides valuable additional background information to embed the flights in the continuous atmospheric context and is used for validation of the airborne results. The development of the boundary layer, derived from backscatter signals of a portable Raman lidar POLLYXT, allows a quick overview of the current vertical structure of atmospheric particles. Ground-based aerosol number concentrations are consistent with the results from flights in heights of a few metres. In addition, a direct comparison of ALADINA aerosol data and ground-based aerosol data, sampling the air at the same location for more than 1 h, shows comparable values within the range of ± 20 %. MASC was operated simultaneously with complementary flight patterns. It is equipped with the same meteorological instruments that offer the possibility to determine turbulent fluxes. Therefore, additional information about meteorological conditions was collected in the lowest part of the atmosphere. Vertical profiles up to 1000 m in altitude indicate a high variability with distinct layers of aerosol, especially for the small particles of a few nanometres in diameter on 1 particular day. The stratification was almost neutral and two significant aerosol layers were detected with total aerosol number concentrations up to 17 000 ± 3400 cm−3 between 180 and 220 m altitude and 14 000 ± 2800 cm−3 between 550 and 650 m. Apart from those layers, the aerosol distribution was well mixed and reached the total number concentration of less than 8000 ± 1600 cm−3. During another day, the distribution of the small particles in the lowermost ABL was related to the stratification, with continuously decreasing number concentrations from 16 000 ± 3200 cm−3 to a minimum of 4000 ± 800 cm−3 at the top of the inversion at 320 m. Above this, the total number concentration was rather constant. In the region of 500 to 600 m altitude, a significant difference of both CPCs was observed. This event occurred during the boundary layer development in the morning and represents a particle burst within the ABL

The COTUR project: remote sensing of offshore turbulence for wind energy application

The paper presents the measurement strategy and data set collected during the COTUR (COherence of TURbulence with lidars) campaign. This field experiment took place from February 2019 to April 2020 on the southwestern coast of Norway. The coherence quantifies the spatial correlation of eddies and is little known in the marine atmospheric boundary layer. The study was motivated by the need to better characterize the lateral coherence, which partly governs the dynamic wind load on multi-megawatt offshore wind turbines. During the COTUR campaign, the coherence was studied using land-based remote sensing technology. The instrument setup consisted of three long-range scanning Doppler wind lidars, one Doppler wind lidar profiler and one passive microwave radiometer. Both the WindScanner software and LidarPlanner software were used jointly to simultaneously orient the three scanner heads into the mean wind direction, which was provided by the lidar wind profiler. The radiometer instrument complemented these measurements by providing temperature and humidity profiles in the atmospheric boundary layer. The scanning beams were pointed slightly upwards to record turbulence characteristics both within and above the surface layer, providing further insight on the applicability of surface-layer scaling to model the turbulent wind load on offshore wind turbines. The preliminary results show limited variations of the lateral coherence with the scanning distance. A slight increase in the identified Davenport decay coefficient with the height is partly due to the limited pointing accuracy of the instruments. These results underline the importance of achieving pointing errors under 0.1∘ to study properly the lateral coherence of turbulence at scanning distances of several kilometres.publishedVersio

ALADINA - An unmanned research aircraft for observing vertical and horizontal distributions of ultrafine particles within the atmospheric boundary layer

This paper presents the unmanned research aircraft Carolo P360 "ALADINA" (Application of Light-weight Aircraft for Detecting IN situ Aerosol) for investigating the horizontal and vertical distribution of ultrafine particles in the atmospheric boundary layer (ABL). It has a wingspan of 3.6 m, a maximum take-off weight of 25 kg and is equipped with aerosol instrumentation and meteorological sensors. A first application of the system, together with the unmanned research aircraft MASC (Multi-Purpose Airborne Carrier) of the Eberhard Karls University of Tübingen (EKUT), is described. As small payload for ALADINA, two condensation particle counters (CPC) and one optical particle counter (OPC) were miniaturised by re-arranging the vital parts and composing them in a space-saving way in the front compartment of the airframe. The CPCs are improved concerning the lower detection threshold and the response time to less than 1.3 s. Each system was characterised in the laboratory and calibrated with test aerosols. The CPCs are operated in this study with two different lower detection threshold diameters of 11 and 18 nm. The amount of ultrafine particles, which is an indicator for new particle formation, is derived from the difference in number concentrations of the two CPCs (ΔN). Turbulence and thermodynamic structure of the boundary layer are described by measurements of fast meteorological sensors that are mounted at the aircraft nose. A first demonstration of ALADINA and a feasibility study were conducted in Melpitz near Leipzig, Germany, at the Global Atmosphere Watch (GAW) station of the Leibniz Institute for Tropospheric Research (TROPOS) on 2 days in October 2013. There, various ground-based instruments are installed for long-term atmospheric monitoring. The ground-based infrastructure provides valuable additional background information to embed the flights in the continuous atmospheric context and is used for validation of the airborne results. The development of the boundary layer, derived from backscatter signals of a portable Raman lidar POLLYXT, allows a quick overview of the current vertical structure of atmospheric particles. Ground-based aerosol number concentrations are consistent with the results from flights in heights of a few metres. In addition, a direct comparison of ALADINA aerosol data and ground-based aerosol data, sampling the air at the same location for more than 1 h, shows comparable values within the range of ± 20 %. MASC was operated simultaneously with complementary flight patterns. It is equipped with the same meteorological instruments that offer the possibility to determine turbulent fluxes. Therefore, additional information about meteorological conditions was collected in the lowest part of the atmosphere. Vertical profiles up to 1000 m in altitude indicate a high variability with distinct layers of aerosol, especially for the small particles of a few nanometres in diameter on 1 particular day. The stratification was almost neutral and two significant aerosol layers were detected with total aerosol number concentrations up to 17 000 ± 3400 cm−3 between 180 and 220 m altitude and 14 000 ± 2800 cm−3 between 550 and 650 m. Apart from those layers, the aerosol distribution was well mixed and reached the total number concentration of less than 8000 ± 1600 cm−3. During another day, the distribution of the small particles in the lowermost ABL was related to the stratification, with continuously decreasing number concentrations from 16 000 ± 3200 cm−3 to a minimum of 4000 ± 800 cm−3 at the top of the inversion at 320 m. Above this, the total number concentration was rather constant. In the region of 500 to 600 m altitude, a significant difference of both CPCs was observed. This event occurred during the boundary layer development in the morning and represents a particle burst within the ABL

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state.These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere.Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions.Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period.Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations