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Direct Determination of Ground-State Transition Widths and Natural Level Widths with the Method of Relative Self Absorption
摘要： The method of relative self absorption is based on the technique of nuclear resonance ?uorescence measurements. It allows for a model-independent determination of ground-state transition widths, natural level widths, and, consequently, of branching ratios to the ground state for individual excitations. Relative self-absorption experiments have been performed on the nuclei 6Li and 140Ce. In order to investigate the total level width for the 0+1 , T = 1 level at 3563 keV in 6Li, a high-precision self-absorption measurement has been performed. In the case of 140Ce, self absorption has been applied for the ?rst time to study decay widths of dipole-excited states in the energy regime of the pygmy dipole resonance.
关键词： 6Li,natural level widths,nuclear resonance fluorescence,ground-state transition widths,140Ce,branching ratios,relative self absorption,pygmy dipole resonance
更新于2025-09-23 15:21:21
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Double-passage mechanical cooling in a coupled optomechanical system
摘要： We consider a three-mode optomechanical system where two cavity modes are coupled to a common mechanical oscillator. We focus on the resolved sideband limit and illustrate the relation between the significant parameters of the system and the instantaneous-state mean phonon number of the oscillator optical coupling set up a correlation between the two cavity modes, which has significant effect on the cooling process. Using numerical solutions, we find that the inter-cavity coupling will decrease the cooling effect when both cavities have the same effective optomechanical coupling. However, when the effective optomechanical couplings are different, the cooling effect will be strongly improved by selecting appropriate range of inter-cavity coupling.
关键词： Ground-state cooling,Optomechanical system,Quantum optics
更新于2025-09-19 17:13:59
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Neutral ground state particle density measurement of xenon plasma in microwave cathode by two-photon laser-induced fluorescence spectroscopy
摘要： This paper reports the first study to measure xenon neutral ground state particle density of microwave cathode by two-photon laser induced fluorescence spectroscopy (TALIF). Xenon is commonly used as a propellant in electric propulsion like Hall thrusters, ion thrusters, and their cathodes. For electric propulsion, information about neutral particles is important such as the ionization degree and the charged exchange collisions (CEX). The measurement target is XeI 6p[3/2]2, which absorbs at a wavelength of 224.29 nm and emits fluorescence of 834.7 nm. The measurement system was demonstrated for three cases: cold gas, without electron extraction, with electron extraction. From three cases, the measurement system can detect a neutral ground state particle density of order without and with a plasma. In a cold gas, the neutral ground state particle density is 8.4 × 10^19 m^-3 at 0.098 mg/s. Without electron extraction, the neutral ground density decreases by ionization and excitation With electron extraction, the density varied from 0.6 to 2.3 times compared to without electron extraction depending on anode voltage.
关键词： electric propulsion,TALIF,neutral ground state particle density,microwave cathode,xenon
更新于2025-09-16 10:30:52
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Resolved-Sideband Cooling of a Levitated Nanoparticle in the Presence of Laser Phase Noise
摘要： We investigate the influence of laser phase noise heating on resolved sideband cooling in the context of cooling the center-of-mass motion of a levitated nanoparticle in a high-finesse cavity. Although phase noise heating is not a fundamental physical constraint, the regime where it becomes the main limitation in Levitodynamics has so far been unexplored and hence embodies from this point forward the main obstacle in reaching the motional ground state of levitated mesoscopic objects with resolved sideband cooling. We reach minimal center-of-mass temperatures comparable to Tmin ? 10 mK at a pressure of p ? 3 × 10?7 mbar, solely limited by phase noise. Finally we present possible strategies towards motional ground state cooling in the presence of phase noise.
关键词： levitated nanoparticle,laser phase noise,resolved sideband cooling,ground state cooling,optomechanical cooling
更新于2025-09-16 10:30:52
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Study on Solvent Effect and Estimation of Dipole Moments of Laser Dye 3ADHC
摘要： In this paper solvent effect of 3-acetyl-7-(diethylamino)-2H-chromen-2-one (3ADHC) dye molecule have been studied by solvatochromic shift method. The electronic absorption and emission spectra of the dye molecule were recorded in a variety of polar protic and polar aprotic solvents at room temperature (298K). Solvatochromic shifts, specifically bathochromic (red) shifts were observed in the absorption and emission spectra as a result of solvent polarity, it signifies the π→π* transition involved. The ground state dipole moment and excited state dipole moment of 3AHDC is calculated using solvent correlation methods. Obtained results are in good agreement with the ground state dipole moment calculated by Gaussion computational methods. The ground and excited state dipole moment of the 3ADHC have also been computed from ab initio calculations and compared with those determined experimentally. It has been found that excited-state dipole moment (μe) is greater than ground-state dipole moment (μg) for the title molecule. The increase in dipole moment in the excited singlet states ranges between 3.93 to 8.60D for 3ADHC. This demonstrates that test molecule is more polar in excited states than in ground states for all the solvents used. The spectral changes were analyzed by Kamlet-Taft parameters.
关键词： Stokes shift,Solvatochromic,Molecular Structure of 3-acetyl-7-(diethylamino)-2H-chromen-2-one (3ADHC),Ground state and excited state dipole moment
更新于2025-09-12 10:27:22
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Discussion of Photovoltaic Mechanisms of Organic Semiconductor Solar Cells; 有機半導体太陽電池の発電機構に関する一考察;
摘要： We have studied photovoltaic mechanisms of an organic solar cell using phthalocyanine for a p-type semiconductor and fullerene C60 for an n-type semiconductor in quantum chemistry simulation. This study examines computation of the electronic state of the phthalocyanine–fullerene C60 bimolecular system in the ground state by the DFT method using long-range corrected hybrid functional CAM-B3LYP. Some double bonds in unimolecular phthalocyanine become semi-double bonds in the bimolecular system. Furthermore, some carbon atoms in a fullerene molecule are negatively charged in the bimolecular system. These results suggest the generation of positive holes and conduction electrons in the bimolecular system. Investigation of reports about simulation in an excited state and the actual measurement of electric conductivity has revealed that these positive holes and conduction electrons in the ground state facilitate the migration of positive holes and conduction electrons generated in a photoactive layer by light irradiation.
关键词： The ground state,Semi-double bond,Negative charge,DFT method,Organic solar cell,Photovoltaic mechanisms
更新于2025-09-11 14:15:04
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Computational Investigations about the Ground and Excited States?￠????Properties of Trans-4-N,N-Dimethylamino-4?￠????-Nitro-Stilbene (DNS) and Trans-4-N,N-Dimethyl-Amino-4?￠????-Cyanostilbene (DCS) Derivatives
摘要： The ground and lowest-lying singlet excited state geometries and dipole moments of trans-4-N,N-dimethylamino-4’-nitro-stilbene (DNS) derivative and the trans-4-N,N-dimethyl-amino-4’-cyanostilbene (DCS) derivative are calculated at the B3LYP level of theory for the first time in this work. The vertical excitation energies and the fluorescence emission energies are obtained for the two species. The calculated results are compared with available experimental results and show good consistency. The molecular orbital analyses in these molecules have been performed. The comparison of the atomic charge distributions in the ground and excited states of both the DNS derivative and DCS derivative implies the intra molecular charge transfer (ICT) process during the excitation period.
关键词： Ground state,Excitation energy,Fluorescence emission,Molecular orbital,Charge transfer
更新于2025-09-10 09:29:36
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Influence of stacking on the ground and excited states of 2-aminopyridine
摘要： In the present work, the ground and excited electronic state properties of seven isomers of 2-aminopyridine (2AMP) stacked dimer have been investigated at the estimated CCSD(T)/CBS limit and RI-CC2/def2-TZVP levels of theory, respectively. The interaction energy values for the seven isomers fall in the range of -7.7 to -4.9 kcal/mol. The most stable dimer is stabilized by two weak hydrogen bonds as well as by stacking interaction between the two moieties. The performance of several density functional theoretical methods has been tested for the ground state as well as the excited states. For the ground state, the functionals B3LYP-D3 and B97D were found to perform the best, giving a mean absolute deviation of 0.3 kcal/mol. For the excited states, the use of the functionals M06-2X and CAM-B3LYP led to results in good agreement with those of the RI-CC2 method, giving a mean absolute deviation of 2.3 kcal/mol. In addition, the vertical excitation energy values for a single proton transfer in the hydrogen bonded (planar) 2-aminopyridine dimer and double proton transfer in the stacked dimer of (2AMP)2 are also reported.
关键词： stacked dimer,2-aminopyridine,ground state geometry,electronic excited states
更新于2025-09-09 09:28:46
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Improving the cooling of a mechanical oscillator in a dissipative optomechanical system with an optical parametric amplifier
摘要： The ground-state cooling of a macroscopic mechanical oscillator is a crucial prerequisite for implementing the quantum manipulation of the mechanical oscillator. Here we show that a degenerate optical parametric amplifier (OPA) can significantly improve the cooling of the mechanical membrane in the purely dissipative coupling system in the unresolved sideband regime. In the presence of the OPA with a parametric phase π/2, the mechanical membrane can be cooled from room temperature 293 K to 10 mK, a factor of 112 lower than that in the absence of the OPA. If the mechanical oscillator is precooled to 0.1 K, the mechanical membrane can be cooled into the microkelvin regime.
关键词： optical parametric amplifier,dissipative optomechanical system,ground-state cooling,mechanical oscillator
更新于2025-09-04 15:30:14
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Metal-organic frameworks as SERS substrates with high tailorability
摘要： Surface enhanced Raman scattering (SERS) is a widely used analytical technique for detecting trace-level molecules based on an indispensable SERS substrate. SERS substrates with high tailorability are assumed to be attractive and desirable for SERS detection, because the substrates match the need for the selective detection of different species. Nevertheless, the rational design of such SERS substrates is rather challenging for both noble-metal and semiconductor substrates. Herein, expanding beyond conventional SERS substrates, we demonstrate that metal-organic framework (MOF) materials can serve as a type of SERS substrate with molecular selectivity, which are rarely realized for SERS detection without any special pretreatment. A salient structural characteristic of MOF-based SERS substrates benefiting the SERS selectivity is their high tailorability. By controlling the metal centers, organic ligands, and framework topologies of our MOF-based SERS substrates, we show that the electronic band structures of MOF-based SERS substrate can be purposively manipulated to match those of the target analytes, thus resulting in different detectable species. Going further, the SERS enhancement factors (EFs) of the MOF-based SERS substrates can be greatly enhanced to as high as 106 with a low detection limit of 10-8 M by pore-structure optimization and surface modification, which is comparable to the EFs of noble metals without “hot spots” and recently-reported semiconductors. This selective enhancement is interpreted as being due to the controllable combination of several resonances, such as the charge-transfer, interband and molecule resonances, together with the ground-state charge-transfer interactions. Our study opens a new venue for the development of SERS substrates with high-design flexibility, which is especially important for selective SERS detection towards specific analytes.
关键词： Surface enhanced Raman scattering (SERS),tailorability,charge-transfer,molecular selectivity,interband and molecule resonances,enhancement factors (EFs),metal-organic framework (MOF),ground-state charge-transfer interactions,SERS substrates
更新于2025-09-04 15:30:14