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Atom-Varied Side Chains in Conjugated Polymers Affect Efficiencies of Photovoltaic Devices Incorporating Small Molecules
摘要： We synthesized three conjugated polymers involving sulfur(S)-inserted and chlorine(Cl)-substituted side chains of the parent two-dimensional conjugated polymer—poly(benzodithiophene-thiophene-benzooxadiazole) (BO)—to form S-inserted (BO2S), Cl-substituted (BO2Cl) and S-inserted with Cl-substituted (BO2S2Cl) polymers for tuning their surface energies and, thus, interaction with IT-4F small molecule in their binary blends. In the BO:IT-4F blend, the bulk heterojunction (BHJ) structure was constituted mainly from the long-rod BO domains along with a few IT-4F domains that dispersed well in the blend; in contrast, favorable networks for charge transport existed in the BO2S or BO2S2Cl with IT-4F blend. The disk sizes of IT-4F in the BO2S2Cl:IT-4F blend were larger than that in the BO2S:IT-4F blend (23.3 vs. 18.1 nm). As the extent of atom variation increased from BO to BO2S to BO2S2Cl, the induced IT-4F crystallinity increased, and the orientation of molecular packing of the polymer varied. The highest PCE (12.06%) was that for the device based on the double sulfur-inserted/chlorine-substituted side chain polymer and IT-4F acceptor (BO2S2Cl:IT-4F), owing to the more balanced hole-to-electron mobility, being consistent with the value predicted (11.8%) using the random forest machine learning model. This study not only provides insight into the photovoltaic performance of the polymers with atom-inserted or -substituted side chain but also reveals that the effects of molecular packing.
关键词： organic photovoltaics,small molecule acceptor,machine learning,packing orientation,atom-varied polymer side chain
更新于2025-09-12 10:27:22
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AIP Conference Proceedings [AIP Publishing LLC OPTOELECTRONIC MATERIALS AND THIN FILMS: OMTAT 2013 - Kochi, Kerala, India (3–5 January 2013)] - Dynamics of atom-field probability amplitudes in a coupled cavity system with Kerr non-linearity
摘要： We have investigated the dynamics of two cavities coupled together via photon hopping, filled with Kerr non-linear medium and each containing a two level atom in it. The evolution of various atom (field) state probabilities of the coupled cavity system in two excitation sub space are obtained numerically. Detailed analysis has been done by taking different initial conditions of the system, with various coupling strengths and by varying the susceptibility of the medium. The role of susceptibility factor, on the dynamics atom field probability has been examined. In a coupled cavity system with strong photon hopping it is found that the susceptibility factor modifies the behaviour of probability amplitudes.
关键词： Two level atom,Kerr medium,Coupled cavity
更新于2025-09-12 10:27:22
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Single atom laser in normal-superconductor quantum dots
摘要： We study a single-level quantum dot strongly coupled to a superconducting lead and tunnel coupled to a normal electrode which can exchange energy with a single-mode resonator. We show that such a system implements a single atom laser. We employ both a semiclassical treatment and a quantum master-equation approach to characterize the properties of this laser. In particular, we ?nd that this system can be operated with ef?ciency approaching unity; that is, a single photon is emitted into the cavity for every Cooper pair participating in the charge current. We ?nd also that lasing in the proposed setup is clearly identi?able in the transport properties: in the lasing state, the electrical current through the quantum dot is pinned to the maximum value achievable in this hybrid nanostructure, and hence, the onset of lasing can be detected simply by a current measurement.
关键词： semiclassical treatment,quantum dot,Cooper pair,transport properties,superconducting lead,charge current,single atom laser,quantum master-equation approach,single-mode resonator,normal electrode
更新于2025-09-12 10:27:22
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[Advances In Atomic, Molecular, and Optical Physics] Volume 68 || Collective motion of an atom array under laser illumination
摘要： We develop a theoretical formalism for the study of light-induced motion of atoms trapped in a two-dimensional (2D) array, considering the effect of multiple scattering of light between the atoms. We find that the atomic motion can be described by a collective diffusion equation, wherein laser-induced dipole–dipole forces couple the motion of different atoms. This coupling leads to the formation of collective mechanical modes of the array atoms, whose spatial structure and stability depend on the parameters of the illuminating laser and the geometry of the 2D array. We demonstrate the application of our formalism for the analysis of light-induced heating of the 2D array. The presented approach should be useful for treating the optomechanical properties of recently proposed quantum optical platforms made of atomic arrays.
关键词： laser illumination,dipole–dipole interactions,optomechanics,atom array,collective motion
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Fast Photon Storage in a Fiber-Based Atom-Cavity System
摘要： Miniaturized ?ber-based optical resonators are emerging as a robust and scalable technology for realizing ?ber-based quantum networks. First demonstrated in [1], these cavities have been integrated with a variety of emitters, e.g. atoms, ions and solid-state systems, to build single-photon quantum interfaces. Our system consists of a single 87Rb atom coupled to a high bandwidth (κ = 2π×40 MHz (cid:2) γ), single-sided ?ber Fabry-Perot cavity (FFPC), Fig. 1(a). The unique system of four in-vacuum lenses, with their focal points coinciding with the ?ber-cavity center, provides the necessary optical access for 3D-cooling and trapping, addressing and high resolution ?uorescence imaging of the atoms, Fig. 1(b). For the D2-transition of 87Rb, the strongly coupled atom-cavity system shows a sixfold Purcell broadening and 90% emission into the cavity mode [2]. Here we present deterministic generation and storage of fast photon pulses. For single-photon generation the atomic state is prepared in F = 1 ground state. A π?polarized classical control laser pulse creates a single photon in the cavity mode with an ef?ciency of ～80%, Fig. 1(c). The pulse shape of the emitted single photon can be tailored by the temporal shape of the control pulse on a time scale lower than the atomic excited state lifetime of ～26 ns, Fig. 1(d). For the storage of fast (short) coherent light pulses, the atomic system is prepared in the |F = 2, m f = ?2(cid:4) state by optical pumping. The temporally shaped input coherent laser pulse at the single-photon level incidents on the cavity mirror while a π?polarized control classical laser pulse with an optimized temporal pro?le, dresses the atom-cavity system such that the storage ef?ciency of the input pulse is maximised. We store photon pulses with a temporal width down to 10 ns with an overall ef?ciency of ～5%.
关键词： 87Rb atom,single-photon quantum interfaces,photon storage,fiber Fabry-Perot cavity,fiber-based optical resonators,quantum networks
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Structural transformations revealed by in-situ HRTEM observations
摘要： With the recent advance of In-Situ Transmission Electron Microscopy (In-Situ TEM), it has become a very essential technique to understand the structure-property relationships of materials. Here, we demonstrate that the formation mechanism of 1D-Si nanowires is initiated by the atom intrusion into the Si lattice at the interfaces, and the formation process is advanced by the atom intrusion into the Si lattice at the interfaces. The formation mechanism of 1D-Si nanowires is also discussed by the thermodynamic analysis. It is found that the 1D-Si nanowires are formed at the triple junction at the interfaces, and the formation process is advanced by the atom intrusion into the Si lattice at the interfaces. The formation mechanism of 1D-Si nanowires is also discussed by the thermodynamic analysis.
关键词： formation mechanism,atom intrusion,In-Situ TEM,thermodynamic analysis,1D-Si nanowires
更新于2025-09-11 14:15:04
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
摘要： Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to densify the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is necessary, and development of new post processing regimes guaranteeing the best performance of the material is required.
关键词： Hot isostatic pressing (HIP),Atom probe tomography,Transmission electron microscopy,Maraging steel,Precipitation hardening,Laser powder bed fusion
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - The Role of Trap Symmetry in an Atom-Chip Interferometer above the Bose-Einstein Condensation Threshold
摘要： Cold atom interferometers have demonstrated excellent performance and hold great prospects for time, gravity, acceleration and rotation measurements. Trapped interferometers, for example using atom chips, can potentially enable portable applications of theses sensors. Atom chip interferometers have been successfully demonstrated using Bose-Einstein condensates but are subject to the effect of atom-atom interactions which cause phase decoherence. In this study, we proposed an atom chip interferometer using a gas just above the condensation threshold to reduce the interaction effects. This proposal is similar to white light interferometry in the sense that the difference between the optical paths of the two arms must be close to zero to observe fringes. In a trapped interferometer this condition is analogous to maximizing the degree of symmetry between the two trapping potentials. We demonstrated that if the two trapping potentials are harmonic with slightly different curvatures inhomogeneous dephasing arises. This leads to a typical contrast decay time. Here we use 87Rb in the two states |a>=|F=1,mF=-1> and |b>=|F=2,mF=2>. Both states are trapped by the same magnetic field created by an atom chip. As described by the Breit-Rabi formula, the energies of the two levels |a> and |b> have a slightly different magnetic field dependence. We can use this difference to fine tune the curvature difference between the two trapping potentials. We perform Ramsey sequences and record the fringes as a function of the Ramsey time for several temperatures and values of curvature difference. We find a good agreement with the above formula. Coherence times of order 1s have been observed. We will describe the experiment, the model used to extract the contrast decay time and the limitations of this model due to atom interactions. The results open the way for experimental demonstration of atom chip accelerometers and gyroscopes.
关键词： trap symmetry,Ramsey sequences,atom-chip interferometer,Bose-Einstein condensation,coherence times
更新于2025-09-11 14:15:04
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Atom-photon bound states and non-Markovian cooperative dynamics in coupled-resonator waveguides
摘要： We study the properties of atom-photon bound states and single-photon cooperative dynamics in a waveguide system which consists of a finite-bandwidth channel with model dispersion and an ensemble of two-level atoms whose size is ignorable when compared with the lattice constant. The bound states are formed by all atoms and a localized photonic excitation. We find that the effect of atomic collection is equivalent to the case of one atom by rescaling the coupling strength with the square root of the atom number, as far as the eigenenergy equation is concerned. Besides, it is found there is a quantum phase transition when more than one type of atom are present. The characteristic lengths and wave functions are analyzed near the phase transition point. The exact analytical results for the cooperative dynamics at the single excitation level are obtained and we point out the dark state in this system leads to a universal population trapping in the time evolution process. This type of trapping obeys a simple law that is only associated with the atom number. A direct conclusion that results from the trapping law is that the single-photon cooperative emission is suppressed when the number of atoms is large enough.
关键词： coupled-resonator waveguides,quantum phase transition,non-Markovian cooperative dynamics,atom-photon bound states,dark state
更新于2025-09-11 14:15:04
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[IEEE 2019 Joint Conference of the IEEE International Frequency Control Symposium anEuropean Frequency and Time Forum (EFTF/IFC) - Orlando, FL, USA (2019.4.14-2019.4.18)] 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC) - A Novel Laser Activated Atom Source for Portable Strontium Optical Lattice Atomic Clocks
摘要： Atomic clocks have been in common use since the 1950s and over this period the clock community has had two main goals: increasing the performance of the clocks and increasing their portability. At Birmingham we aim to compress a strontium optical lattice clock, a clock with an extremely high accuracy, into a portable package. Many novel approaches need to be employed to allow such a clock to operate with a favorable SWaP while maintaining the low instability and uncertainty that makes optical clocks a desirable frequency standard. The focus of this work is to use laser activation of a strontium compound as the atomic source for the clock. Previously work published by this group [1] demonstrated that it is possible to release the strontium atoms from strontium oxide successfully load a magneto-optical trap (MOT).
关键词： Ultra-stable Laser Sources and Optical Frequency References,Optical Ion and Neutral Atom Clocks
更新于2025-09-11 14:15:04