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Design and preliminary operation of a laser absorption diagnostic for the SPIDER RF source
摘要： The ITER Heating Neutral Beam (HNB) injector is required to deliver 16.7 MW power into the plasma from a neutralised beam of H?/D?, produced by an RF source and accelerated up to 1 MeV. To enhance the H? production, the surface of the acceleration system grid facing the source (the plasma grid) will be coated with Cs because of its low work function. Cs will be routinely evaporated in the source by means of specific ovens. Monitoring the evaporation rate and the distribution of Cs inside the source is fundamental to get the desired performances on the ITER HNB. In order to proper design the source of the ITER HNB and to identify the best operation practices for it, the prototype RF negative ion source SPIDER has been developed and built in the Neutral Beam Test Facility at Consorzio RFX. A Laser Absorption Spectroscopy diagnostic will be installed in SPIDER for a quantitative estimation of Cs density. By using a wavelength tunable laser, the diagnostic will measure the absorption spectrum of the 852 nm line along 4 lines of sight, parallel to the plasma grid surface and close to it. From the absorption spectra the line-integrated density of Cs at ground state will be measured. The design of this diagnostic for SPIDER is presented, with details of the layout and of the key components. A preliminary installation of the diagnostic on the test stand for Cs ovens is also described, together with its first experimental results; the effect of ground state depopulation on collected measurements is discussed and partially corrected.
关键词： Laser absorption spectroscopy,Negative ion source,Heating neutral beam,Caesium
更新于2025-09-11 14:15:04
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Proton-Coupled Electron Transfer Kinetics for the Photoinduced Generation of a Cobalt(III)-Hydride Complex
摘要： Studying the formation of transition metal hydride complexes via proton-coupled electron transfer is important for developing next-generation molecular catalysts for hydrogen evolution. We report herein the study of stepwise photoinduced reduction and protonation of [CoIICp-(dppe)]+ (Cp = cyclopentadienyl, dppe = 1,2-bis-(diphenylphosphino)ethane) to form the corresponding hydride complex [HCoIIICp(dppe)]+. Reaction intermediates were optically tracked using transient absorption spectroscopy, and a combination of experimental fitting and kinetic simulations was used to determine apparent rate constants for electron transfer and proton transfer with a range of acid sources. A linear free energy relationship is observed between measured apparent proton transfer rate constants and acid strength, but marked differences from previously electrochemically determined protonation rate constants are found. These deviations, which stem from ground-state reactivity present in photochemical experiments, highlight the challenges in comparing mechanistic studies using different techniques.
关键词： kinetic simulations,transient absorption spectroscopy,transition metal hydride complexes,proton-coupled electron transfer,hydrogen evolution
更新于2025-09-11 14:15:04
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Laser diagnostics for the electron density of helium low temperature plasmas using saturated absorption spectroscopy
摘要： Helium (He) low temperature plasma with an electron density higher than 10^11 cm^-3 was produced using an inductively coupled plasma source, and the electron density of this plasma was determined using a high-resolution laser spectroscopic technique. To remove the Doppler broadening which is the most dominant line broadening in low temperature plasmas, a saturated absorption spectroscopy system was configured. The Lamb dip was successfully separated from the Doppler broadening for the 2^1S - 4^1P transition of the He plasma using a high-resolution laser beam with a narrow spectral line width (below 1 MHz) at 396.5 nm. The estimated spectral line widths of natural broadening, van der Waals broadening, resonance broadening, and Stark broadening were 40.14 MHz, 0.93 MHz, 0.15 MHz, and 12.60 MHz, respectively, when the He gas pressure was 30 mTorr and 1 kW RF power was applied. The electron density of the He plasmas was determined to be ~3 x 10^11 cm^-3, which was comparable with those determined by a Langmuir probe and optical emission spectroscopy combined with a collisional-radiative model.
关键词： Low temperature plasma,Spectral line broadening,Saturated absorption spectroscopy,Helium
更新于2025-09-11 14:15:04
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Measurement of pressure shift and broadening for Ar and Kr 4s[3/2]2?→?4p[5/2]3 transition in rare gases using diode-laser spectroscopy
摘要： In this work simultaneous measurements of pressure broadening and shift coe?cients for 811.5 nm Ar and 811.3 nm Kr spectral lines of the 4s[3/2] 2 → 4p[5/2] 3 transition were performed. Assessment of gas temperature was done by determining Doppler width components of the lines’ Voigt pro?les. Pressure shift coe?cients for the mixtures Ar:Ne, Kr:Ne and Kr:Ar were determined for the ?rst time. Their values in units of 10 -10, reduced to 300 K are: β Ar:Ne = -0.51 ± 0.05, β Kr:Ne = -0.65 ± 0.01, β Kr:Ar = -2.07 ± 0.08. Additionally we demonstrated the use of easily available starters for ?uorescent lamps as sealed Ar discharge cells for reference optical frequency.
关键词： Spectral line pressure shift,Radio-frequency discharge,Metastable argon and krypton atoms,Optically pumped all-rare-gas laser,Diode-laser absorption spectroscopy
更新于2025-09-11 14:15:04
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Charge transfer dynamics in chlorophyll-based biosolar cells
摘要： We fabricated a chlorophyll (Chl)-based biosolar cell with H2Chl-sensitized TiO2 as an acceptor and (ZnChl)n as a donor. This solar cell gives a relatively high quantum yield from the absorption spectral contribution from both the donor and acceptor species. We employed subpicosecond time-resolved absorption spectroscopy (TAS) to study the excited state dynamics at the Chl interface. A charge transfer (CT) state between TiO2–H2Chl and (ZnChl)n was observed at 640 nm after excitation at the Qy peaks, 680 nm and 720 nm. This CT state is entirely different from the CT states observed for either TiO2–H2Chl (TiO2–H2Chl/spiro-OMeTAD) or TiO2–(ZnChl)n systems. Due to the slower charge transfer process from H2Chl+ to TiO2 as compared to that from (ZnChl)n+ to H2Chl, the CT lifetimes of H2Chl–(ZnChl)n+ (t1 = 0.1 ps, t2 = 1.4 ps) excited at 720 nm are slightly shorter than that excited at 680 nm (t1 = 0.2 ps, t2 = 5.6 ps). The TAS results suggest that the interface of TiO2–H2Chl and (ZnChl)n not only transfers holes as spiro-OMeTAD does, but also provides a built-in field for charge dissociation between the two Chl species.
关键词： TiO2,charge transfer,biosolar cell,chlorophyll,time-resolved absorption spectroscopy
更新于2025-09-11 14:15:04
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Single-step formation of Cr 2 N nanoparticles by pulsed laser irradiation
摘要： Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr2N, which is commonly reported together with the conversion of Cr2N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0:35–0:05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr2N with a hexagonal structure corroborate the formation of surface plasmons.
关键词： transmission electron microscopy,liquid nitrogen,chromium nitride nanoparticles,density functional theory,laser irradiation,UV-Vis absorption spectroscopy
更新于2025-09-11 14:15:04
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Improved Charge Separation and Photovoltaic Performance of BiI <sub/>3</sub> Absorber Layers by Use of an In Situ Formed BiSI Interlayer
摘要： Stable and nontoxic bismuth iodide (BiI3) is emerging as a promising absorber material for solar cell applications as it possesses favorable optical properties such as a narrow bandgap (1.7 eV) and a high absorption coe?cient (105 cm?1) in the visible region. Despite these promising features, solar cells employing this material have only achieved power conversion e?ciencies in the region of 1% as of yet, which is distant from the theoretical e?ciency limit of 28%. It is reasonable to suppose that the relatively low performance of BiI3-based solar cells may originate from very short carrier lifetimes (180?240 ps) in BiI3, which makes e?cient separation of mobile charges a crucial factor for the improvement of the photovoltaic performance of this material. Herein, transient optical spectroscopy is employed to show that the use of a bismuth sul?de iodide interlayer between the electron transport layer (ETL) and the bismuth iodide absorber promotes e?cient charge separation. On the basis of this knowledge, we report BiI3 solar cells with a power conversion e?ciency of 1.21% using a solar cell architecture comprised of ITO/SnO2/BiSI/BiI3/organic HTM/Au.
关键词： solar cell,charge separation,transient absorption spectroscopy,BiSI,BiI3
更新于2025-09-11 14:15:04
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Simultaneous two cross-sectional measurements of NH<sub>3</sub> concentration in bent pipe flow using CT-tunable diode laser absorption spectroscopy
摘要： Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NOx by NH3 which is provided by a hydrolysis of urea water. Concentration distribution of NH3 in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH3 slip and urea deposit. Therefore, it is necessary to measure two-dimensional (2D) concentration of NH3 in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH3 concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). Theoretical NH3 concentration distribution which was reconstructed by CT agreed to CFD results and quadruple pipe’s results showed good resolution by 14th order reconstruction. Therefore, this method has enough resolution and accuracy for measuring the concentration distribution of NH3. And this method was employed in a bent pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH3 show differences of the concentration distribution of NH3 each cross-section and flow pattern like swirl flow. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH3 and observe characteristics of flow. In addition, observing flow pattern enable to validate CFD results, and it helps to improve efficiency of after treatment system.
关键词： Urea selective catalytic reduction,NH3 concentration measurement,Exhaust aftertreatment,CT tunable diode laser absorption spectroscopy,Measurement and instrumentation
更新于2025-09-11 14:15:04
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Symmetry of molecular Rydberg states revealed by XUV transient absorption spectroscopy
摘要： Transient absorption spectroscopy is utilized extensively for measurements of bound- and quasibound-state dynamics of atoms and molecules. The extension of this technique into the extreme ultraviolet (XUV) region with attosecond pulses has the potential to attain unprecedented time resolution. Here we apply this technique to aligned-in-space molecules. The XUV pulses are much shorter than the time during which the molecules remain aligned, typically <100 fs. However, transient absorption is not an instantaneous probe, because long-lived coherences re-emit for picoseconds to nanoseconds. Due to dephasing of the rotational wavepacket, it is not clear if these coherences will be evident in the absorption spectrum, and whether the properties of the initial excitations will be preserved. We studied Rydberg states of N2 and O2 from 12 to 23 eV. We were able to determine the polarization direction of the electronic transitions, and hence identify the symmetry of the final states.
关键词： transient absorption spectroscopy,extreme ultraviolet,attosecond pulses,molecular alignment,Rydberg states
更新于2025-09-11 14:15:04
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Influence of Light Coupling Configuration and Alignment on the Stability of HWG-Based Gas Sensor System for Real-Time Detection of Exhaled Carbon Dioxide
摘要： A mid-infrared tunable diode laser absorption spectroscopy (TDLAS) gas sensor based on hollow waveguide (HWG) gas cell for real-time exhaled carbon dioxide (eCO2) detection is reported. A 2.73 μm distributed feedback (DFB) laser was used to target a strong CO2 absorption line, and wavelength modulation spectroscopy (WMS) with the second harmonic (WMS-2 f ) was used to retrieve the CO2 concentration with high sensitivity. The influence of different parameters, including coupling configuration of HWG, laser-to-HWG and HWG-to-detector coupling alignment on the stability of the HWG sensor is systematically studied. The HWG eCO2 sensor showed a fast response time of 2.7s, detection limit of 17 ppmv, and measurement precision of 20.9 ppmv with a 0.54 s temporal resolution. The eCO2 concentrations changed in breath cycles were measured in real time. The Allan variance indicated that the detection limit can reach 1.7 ppmv, corresponding to a detection sensitivity of 1.3×10?8 cm?1 Hz?1/2, as the integration time increases to 26 s. This work demonstrates the performance characteristics and merits of HWG eCO2 sensor for exhaled breath analysis and potential detection for other exhaled gases.
关键词： hollow waveguide,distributed feedback laser,carbon dioxide,Tunable diode laser absorption spectroscopy
更新于2025-09-11 14:15:04