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Hyperfine structures and isotopic shifts of uranium transitions using tunable laser spectroscopy of laser ablation plumes
摘要： We report isotopic shifts and hyperfine structures of selected U transitions employing tunable spectroscopy viz: laser-induced fluorescence and laser absorption spectroscopy of laser ablation plumes. The plasmas were produced during ns laser ablation on a natural U metal target which contains 0.73% 235U. Our results show that isotopic shifts between 238U and 235U are entangled with hyperfine structures of 235U. Measurements obtained using laser-induced fluorescence are affected by the high absorbance of 238U. Time-resolved laser absorption spectroscopy is carried out for evaluating the optical absorption and estimating the hyperfine constants.
关键词： LIBS,Hyperfine structure,Laser absorption spectroscopy,Isotopic analysis,Uranium,Laser-induced fluorescence,Laser ablation,Tunable laser spectroscopy
更新于2025-09-23 15:19:57
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Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets
摘要： The mass accommodation coefficient, αM, describes the liquid?vapor evaporation and condensation kinetics at interface. In spite of numerous experimental efforts, reliable values of αM are still not available for many substances. Here, we present a novel experimental technique, photothermal single-particle spectroscopy (PSPS), that allows for a robust retrieval of mass accommodation coefficients from three simultaneous independent measurements. PSPS combines resonant photoacoustic absorption spectroscopy with modulated Mie scattering measurements on single particles. We study the mass transport of water on organic aerosol droplets that are optically trapped using counter-propagating tweezers. We find the mass accommodation coefficient of water on a pure model organic that is fully miscible with water to be 0.021 at 296 K and to decrease by more than an order of magnitude when the temperature increases to 309 K. The experimentally observed temperature dependence of αM shows an Arrhenius behavior. Furthermore, the water content of the droplets is found to have a profound effect on αM is observed at low water concentrations, while at elevated water concentrations, we observe a 5-fold increase in αM. The technique presented in this work has the potential to become a reliable method for the retrieval of αM values at liquid?vapor interfaces, which are essential for accurate global climate and pharmaceutical aerosol inhalation modeling, to mention but a few.
关键词： temperature dependence,photoacoustic absorption spectroscopy,optical trapping,water transport,organic aerosol droplets,modulated Mie scattering,mass accommodation coefficient,Arrhenius behavior,PSPS,photothermal single-particle spectroscopy
更新于2025-09-23 15:19:57
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Study on the Simultaneous Measurement of O <sub/>2</sub> and CO Concentrations in the Exhaust Gas of a Methane/Air Flame Using Tunable Diode Laser Absorption Spectroscopy
摘要： Oxygen (O2) and carbon monoxide (CO) are produced in combustion reactions and are important gas species, which are closely related to combustion efficiency and production of air pollutants. O2 generates thermal nitrogen oxide (NOX) by reacting with nitrogen in the air at high temperatures, and the presence of excess O2 also affects the energy efficiency due to increasing exhaust heat energy. CO is generally well known for being a toxic gas, and is a crucial gas species produced by incomplete combustion. However, it is difficult to measure O2 and CO level variations in a huge combustion system, such as used in steel annealing and power plant boilers, because of their harsh environment. Therefore, as a multi-species measurement technique, which is non-intrusive, has a high sensitivity, and high response, tunable diode laser absorption spectroscopy was chosen as the optical method used to measure O2 and CO concentrations in exhaust gases. In this study, experiments were carried out to measure the O2 and CO concentrations in an electrical furnace and a combustion system using direct absorption spectroscopy and wavelength modulation spectroscopy. The measured results were compared with those of a gas analyzer of the electro-chemical (E/C) sensor type. The O2 and CO concentrations were measured in the exhaust gas produced from methane/air flame through adjustment of the equivalence ratio to form both, fuel-lean and rich conditions. In order to measure the O2 and CO concentrations precisely and without interference from other combustion products, visible and near-infrared wavelength regions at 760.8 and 2325.2 nm were selected, respectively.
关键词： Carbon Monoxide,Absorption Spectroscopy,Methane,Oxygen
更新于2025-09-23 15:19:57
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Ultrahigh resolution spectroscopy for dimethyl sulfide at the ??1- and ??8-bands by a distributed feedback interband cascade laser
摘要： The ultrahigh-resolution, air-broadened mid-infrared absorption spectrum of dimethyl sulfide (DMS) was recorded in the spectral region of 2994.17–2999.03 cm?1, where the strong ν1-/ν8-bands are located. Benefitting from the tunable laser absorption spectrometry with a distributed feedback interband cascade laser, the spectral resolution achieved 5.69 × 10?6 cm?1. The recorded spectra of DMS are very close to that in the Pacific Northwest National Laboratory (PNNL) database, however it has a much lower absorbance uncertainty of 0.38%. And the maximum relative difference of the full width at half maximum and the integrated area of spectral peaks between the recorded spectra and the PNNL data are as large as 16.7% and 27.9%, respectively, which could mainly come from the difference of the spectral resolution. The more accurate reference spectrum is hopeful to be applied to absolute measurement and remote sensing for gaseous DMS.
关键词： Tunable laser absorption spectroscopy (TLAS),Dimethyl sulfide (DMS),Ultrahigh-resolution spectrum,Interband cascade laser (ICL),Mid-infrared
更新于2025-09-23 15:19:57
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Influence of Halide Ions on the Structure and Properties of Copper Indium Sulphide Quantum Dots
摘要： In the synthesis of CuInS2 quantum dots (QDs), the halide ions present in the copper salts influence the QD growth and optical properties. X-ray absorption spectroscopy allowed rationalizing the halide incorporation in the lattice and the dependency of electronic properties of the material on the ion’s polarizability and interaction with hydrophobic moieties.
关键词： optical properties,halide ions,CuInS2 quantum dots,X-ray absorption spectroscopy
更新于2025-09-23 15:19:57
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Gas distribution mapping for indoor environments based on laser absorption spectroscopy: Development of an improved tomographic algorithm
摘要： Gas distribution mapping (GDM) is an important technology for the study of indoor environment, which can be used to evaluate the efficiency of environmental control system and identify pollutant sources. Most recent studies have implemented GDM through contact sensors or a sensor network, which is difficult to calibrate all the sensors and cover the whole space. In this study, we introduced the non-contact tunable diode laser absorption spectroscopy (TDLAS) technology for GDM in the indoor environment. An improved tomographic algorithm, namely Least Square with Tikhonov Regularization (LSTR), was proposed and compared with two available tomographic algorithms using four validated computational fluid dynamics (CFD) simulations. We also analyzed the effects of the laser emitter placements and optical path densities on the concentration field reconstruction quantitatively. The results showed that the LSTR method could reduce the average relative root mean square error (RRMSE) of tomography by 52%, and the laser emitter at the long edge middle (LEM) can achieve better tomographic performance. The degree of the concentration dispersion from the source would mainly impact the tomographic results: when the sector dispersion (SD) value of concentration distribution was about 2.3 times larger, the average RRMSE value would be decreased by about 40%. The intersection matrix with a higher path density achieved a more accurately reconstructed map due to its lower condition number. In addition, the optical path density was suggested to twice the number of grid cells considering the trade-off between scanning time and accuracy.
关键词： Non-contact sensing,Tunable diode laser absorption spectroscopy (TDLAS),Concentration measurement,Indoor air,Air pollution
更新于2025-09-23 15:19:57
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Deepa??Blue Thiophenea??Based Steric Oligomers as a Lowa??Threshold Laser Gain and Host Material
摘要： Thiophene-based (Th-based) derivatives have received wide attentions in organic optoelectronics due to their excellent and tuneable optoelectrical properties as well as chemical modification. However, the low photoluminescence quantum yield in solid state limits their application in solution-processed light-emitting optoelectronic devices, especially in organic lasers. Herein, a novel blue-emitting steric Th-based fluorophore (MC8-Th) with excellent optical gain behavior for organic laser is reported. Interestingly, MC8-Th neat film exhibits efficient exceptional deep-blue amplified spontaneous emission (ASE) behavior with a remarkably low threshold of 6.0 μJ cm?2 and full-width-at-half-maximum value of 2.6 nm. Furthermore, random laser signals are also obtained with the lowest threshold of 4.1 μJ cm?2 when incorporating the compound into an inert polystyrene (PS) matrix. In addition, low threshold (16 μJ cm?2, fivefold lower than those of F8BT neat films) yellow–green ASE emission (560 nm) is achieved through F?rster resonance energy transfer. Meanwhile, ultrafast transient absorption spectroscopy is deployed here to observe the single-molecular excitonic behavior in solution and PS-blend, intermolecular excited state in neat film, and efficient energy transfer in MC8-Th:F8BT-blend films. As far as known, MC8-Th shows lower threshold ASE/lasing behavior for the Th-based conjugated materials.
关键词： transient absorption spectroscopy,optical gain behavior,organic laser,thiophene-based derivatives,F?rster resonance energy transfer
更新于2025-09-23 15:19:57
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Strong Spin-Selective Optical Stark Effect in Lead Halide Perovskite Quantum Dots
摘要： The optical Stark effect (OSE) stems from a coherent, nonlinear interaction between a transition and a non-resonant light field, which usually causes a blue-shift of the transition energy. This shift can be understood using the picture of so-called photon-dressed states or Floquet states. The perturbation induced by a light filed which is periodical in time results in a series of quasi-static Floquet eigenstates periodically spaced in units of the photon energy. The repulsion (hybridization) between the Floquet and equilibrium states causes a blueshift of the transition between the equilibrium states, as schematically shown in Fig. 1a. The OSE effect is intrinsically helicity-selective, that is, a left circularly polarized light couples only to the |0> to |+1> but not the |0> to |-1> transition and vice versa (the number in the ket is the azimuthal quantum number of the total angular momentum). Experimentally, the OSE can be conveniently observed using circularly polarized transient absorption (TA) spectroscopy. With a co-circularly polarized pump-probe configuration, the probe pulse measures a blue-shifted transition in the duration of the pump pulse and a derivative-like difference spectrum (with respect to the unpumped spectrum) can be detected (Fig. 1b), whereas with a counter-circularly polarized configuration nothing can be detected if multi-photon absorption is negligible.
关键词： transient absorption spectroscopy,optical Stark effect,spin-selective,lead halide perovskite,quantum dots
更新于2025-09-23 15:19:57
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Delocalization boosts charge separation in organic solar cells
摘要： Organic solar cells (OSCs) utilizing π-conjugated polymers have attracted widespread interest over the past three decades because of their potential advantages, including low weight, thin film flexibility, and low-cost manufacturing. However, their power conversion efficiency (PCE) has been far below that of inorganic analogs. Geminate recombination of charge transfer excitons is a major loss process in OSCs. This paper reviews our recent progress in using transient absorption spectroscopy to understand geminate recombination in bulk heterojunction OSCs, including the impact of polymer crystallinity on charge generation and dissociation mechanisms in nonfullerene acceptor-based OSCs. The first example of a high PCE with a small photon energy loss is also presented. The importance of delocalization of the charge wave function to suppress geminate recombination is highlighted by this focus review.
关键词： Polymer crystallinity,Power conversion efficiency,Organic solar cells,Transient absorption spectroscopy,Dissociation mechanisms,Photon energy loss,π-conjugated polymers,Charge generation,Nonfullerene acceptor,Geminate recombination
更新于2025-09-23 15:19:57
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Symmetry controlled photo-selection and charge separation in butadiyne-bridged donora??bridgea??acceptor compounds
摘要： Electron transfer (ET) in donor-bridge-acceptor (DBA) compounds depends strongly on the structural and electronic properties of the bridge. Among the bridges that support donor - acceptor conjugation, alkyne bridges have attractive and unique properties: they are compact, possess linear structure permitting access to high symmetry DBA structures, and allow torsional motion of D and A, especially for longer bridges. We report conformation dependent electron transfer dynamics in a set of novel DBA compounds featuring butadiyne (C4) bridge, N-isopropyl-1,8-napthalimide (NAP) acceptors, and donors that span a range of reduction potentials (trimethyl silane (Si-C4-NAP), phenyl (Ph-C4-NAP), and dimethyl aniline (D-C4-NAP)). Transient mid-IR absorption spectra of the C≡C bridge stretching modes, transient spectra in the visible range and TD-DFT calculations were used to decipher the ET mechanisms. We found that the electronic excited state energies and, especially, the transition dipoles (S0→Sn) depend strongly on the dihedral angle (θ) between D and A and the frontier orbital symmetry, offering an opportunity to photo-select particular excited states with specific ranges of dihedral angles by exciting at chosen wavelengths. For example, excitation of D-C4-NAP at 400 nm predominantly prepares an S1 excited state in the planar conformations (θ ~ 0) but selects an S2 state with θ ~ 90o, indicating the dominant role of the molecular symmetry in the photophysics. Moreover, the symmetry of the frontier orbitals of such DBA compounds not only defines the photo-selection outcome, but also determines the rate of the S2→S1 charge separation reaction. Unprecedented variation of the S2-S1 electronic coupling with θ by over four orders of magnitude results in slow ET at θ ca. 0o and 90o but extremely fast ET at θ of 20-60o. The unique features of high-symmetry alkyne bridged DBA structures enable frequency dependent ET rate selection and make this family of compounds promising targets for the vibrational excitation control of ET kinetics.
关键词： transient absorption spectroscopy,electron transfer,donor-bridge-acceptor,TD-DFT calculations,butadiyne bridge
更新于2025-09-23 15:19:57