Showing papers on "Stark effect published in 1994"
TL;DR: A significant asymmetry in the effective dielectric strength of the protein complex along the two potential electron transfer pathways, with a substantially higher dielectrics strength along the functional pathway is revealed.
Abstract: Although the three-dimensional structure of the bacterial photosynthetic reaction center (RC) reveals a high level of structural symmetry, with two nearly equivalent potential electron transfer pathways, the RC is functionally asymmetric: Electron transfer occurs along only one of the two possible pathways. In order to determine the origins of this symmetry breaking, the internal electric field present in the RC when charge is separated onto structurally characterized sites was probed by using absorption band shifts of the chromophores within the RC. The sensitivity of each probe chromophore to an electric field was calibrated by measuring the Stark effect spectrum, the change in absorption due to an externally applied electric field. A quantitative comparison of the observed absorption band shifts and those predicted from vacuum electrostatics gives information on the effective dielectric constant of the protein complex. These results reveal a significant asymmetry in the effective dielectric strength of the protein complex along the two potential electron transfer pathways, with a substantially higher dielectric strength along the functional pathway. This dielectric asymmetry could be a dominant factor in determining the functional asymmetry of electron transfer in the RC.
266 citations
TL;DR: In this paper, the authors report an in depth study of the properties in the AlInAs/GaInAs heterostructure material system grown by molecular beam epitaxy and show that by judicious control of the tunnel coupling between wells and of the thickness of the latter one can design the wavefunctions and the energy levels in such a may that these new structures behave as quasi-molecules with extremely large dipole matrix elements and strongly field tunable nonlinear optical properties.
Abstract: Coupled quantum wells present unique opportunities for engineering new semiconductors with large optical nonlinearities associated with intersubband transitions in the infrared. In this paper we report an in depth study of these properties in the AlInAs/GaInAs heterostructure material system grown by molecular beam epitaxy. We show that by judicious control of the tunnel coupling between wells and of the thickness of the latter one can design the wavefunctions and the energy levels in such a may that these new structures behave as quasi-molecules with extremely large dipole matrix elements and strongly field tunable nonlinear optical properties. Structures with giant nonlinear susceptibilities /spl chi//sup (2)/(2/spl omega/) and /spl chi//sup (3)/(3/spl omega/) (compared to the bulk constituents of the quantum wells) have been designed and demonstrated. They exhibit large linear Stark shifts of the intersubband transitions which have been used to efficiently tune the nonlinear susceptibilities. The second order nonlinear susceptibility |/spl chi//sup (2)/(2/spl omega/)| exhibits a peak as a function of the electric field corresponding to the energy levels being made equally spaced via the Stark effect. In a three-coupled-well structure triply resonant third harmonic generation has been observed. This process is associated with four equally spaced bound states. The corresponding |/spl chi//sub (3/spl omega/)//sup (3)/| (10/sup -14/ (m/V)/sup 2/ at 300 K and 4/spl times/10/sup -14/ (m/V)/sup 2/ at 30 K) is the highest measured third order noniinear susceptibility in any material. The equivalent of multiphoton ionization of a molecule has also been investigated in this structure. Electrons are photoexcited to a continuum resonance above the barrier via a three-photon transition enhanced by intermediate energy levels. The effect of this resonance on /spl chi//sup (3)/(3/spl omega/) as the electric field is varied is also investigated. Finally, appropriate figures of merit are discussed. >
175 citations
TL;DR: In this article, a simple model was proposed to evaluate the degree of l and ml mixing in high Rydberg states that results from perturbations caused by weak, homogeneous dc electric fields and static ions.
Abstract: We present a simple model to evaluate the degree of l and ml mixing in high Rydberg states that results from perturbations caused by weak, homogeneous dc electric fields and static ions. This model predicts the lifetime of these states qualitatively and explains several seemingly contradictory observations obtained using zero‐kinetic‐energy (ZEKE) photoelectron spectroscopy. The presence of a small homogeneous dc electric field and a few ions in the sample volume causes ml mixing in general as well as l mixing, both of which contribute to the lengthening of the lifetimes. Consequently, the lifetime lengthening appears to be insensitive to the sample pressure. The effect of the dc electric field on the lifetime is complex. Although the electric field results in l mixing, with increasing field strength it inhibits ml mixing, and, at still higher field strength, induces ionization. The variation of the lifetimes with ion concentration is also complicated. At low ion concentration, the ml mixing varies across...
142 citations
TL;DR: In this paper, the Stark effect on the electronic absorption spectrum of CdSe nanocrystals has been studied for all but the smallest clusters, and a second derivative line shape is observed, indicative of a dipole moment in the excited state.
Abstract: The Stark effect on the electronic absorption spectrum of CdSe nanocrystals has been studied for nanocrystals ranging in size from 80 to 20 A in diameter. For all but the smallest clusters, a second derivative line shape is observed, indicative of a dipole moment in the excited state. This result is independent of the surface modification and appears in both CdS and CdSe systems. The Δμ ranges from 15±10 D in the smallest clusters and up to 100±10 D in the largest; however, the increase is not monotonic, and in the very largest clusters studied (d≳70 A), the dipole moment decreases. The dipolar character is lost in clusters less than 25 A. These results can be explained by a model in which there is resonance of an interior state with a surface state at a particular size, with the mixing occurring on a preferred axis.
94 citations
TL;DR: In this article, the optical Stark effect of a two-level system coupled to a Brownian oscillator is studied using equations of motion for a reduced density matrix, which can be used to study the combined effects of strong fields and dephasing processes at finite temperature and interpolate continuously from the coherent to the overdamped limits where they reduce to the stochastic Gaussian-Markovian equation.
Abstract: The optical Stark effect of a two-level system coupled to a Brownian oscillator (i.e. a harmonic mode which in turn is coupled to a heat bath) is studied using equations of motion for a reduced density matrix. These equations, derived using path integral techniques, can be used to study the combined effects of strong fields and dephasing processes at finite temperature, and interpolate continuously from the coherent to the overdamped limits where they reduce to the stochastic Gaussian-Markovian equation. Numerical calculations of probe absorption spectra for various pump intensities are presented, and show dynamical Stark splitting. In contrast to the Bloch equations which contain an infinite-temperature dephasing, we find that at finite temperature, the Stark peaks may have different heights even when the pump pulse is on resonance.
94 citations
TL;DR: In this article, the mid-infrared (λ∼5 μm) luminescence is generated by electron injection into AlInAs/GaInAs coupledquantum wells via a pseudo-quaternary graded gap alloy.
Abstract: Electroluminescence associated with intersubband transition energies greater than the optical phonon energy and at temperatures as high as 300 K is reported. The mid‐infrared (λ∼5 μm) luminescence is generated by electron injection into AlInAs/GaInAs coupled‐quantum wells via an AlInAs/GaInAs pseudoquaternary graded gap alloy. Optical powers up to a few nanowatts and linear in the drive current have been measured. The large Stark shift of the luminescence peak demonstrates the photon‐assisted tunneling nature of the transition. The temperature independence of the luminescence slope efficiency in the 10–100 K range and the linearity of the optical power versus drive current provide strong evidence of population inversion.
77 citations
TL;DR: In this paper, the dielectric response of the semiconductor band edge in a dynamic density matrix model is described based on a set of χ3-relevant constitutive equations involving two-, four-and six-point density matrices.
Abstract: We describe the dielectric response of the semiconductor band edge in a dynamic density matrix model. Our treatment is based on a set of χ3-relevant constitutive equations involving two-, four- and six-point density matrices. We demonstrate that under certain conditions all contributions to the third order susceptibility can be expressed in terms of excitonic and biexcitonic transitions. As a first application of these χ3-relevant equations we investigate the influence of the biexciton on the optical Stark effect in CuCl. We calculate shifts and lineshapes. Our results turn out to be in excellent agreement with experiments as well as with other theoretical predictions.
63 citations
TL;DR: In this paper, the authors investigated the J-aggregates in aqueous solution at room temperature with tunable fs pulses using near-resonant excitation at 565 nm and showed that the coherent response of the Jband is observed at short times leading to a precursor of the dynamic Stark effect similar to recent findings for excitonic transitions in semiconductors.
56 citations
TL;DR: In this article, a model vibronic Hamiltonian was developed to reproduce a wide variety of optical spectra (absorption, hole burning, and Stark effect) from the P * band of the photosynthetic reaction center of Rb. sphaeroides.
Abstract: We have developed a model vibronic Hamiltonian which successfully reproduces a wide variety of optical spectra (absorption, hole burning, and Stark effect) from the P * band of the photosynthetic reaction center of Rb. sphaeroides. A key component of the model is coupling of the Q y states of the special pair bacteriochlorophylls to an internal charge-separated state of the dimer. The model is parametrized to fit wildtype optical spectra and then tested by simulating the absorption and Stark effect spectra from the heterodimer mutants with a minimum of adjustable parameters. The agreement with experiment of the latter results suggests that the basic features of the model are correct
55 citations
TL;DR: This work reports measured Stark widths and shifts, and transition probabilities for a large nubmer of Xe II spectral lines, and a method is proposed to find simultaneously the plasma temperature and the transition probabilities from relative intensity measurements of spectral lines.
Abstract: This work reports measured Stark widths and shifts, and transition probabilities for a large nubmer of Xe ii spectral lines. A pulsed arc was used as a plasma source. The electron density, determined by interferometry at one wavelength, and simultaneously by the Stark broadening of the 5016-\AA{} He i line, covers a range of (0.2--1.8)\ifmmode\times\else\texttimes\fi{}${10}^{23}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$. A method is proposed to find simultaneously the plasma temperature and the transition probabilities from relative intensity measurements of spectral lines. Electron temperatures are in the range of 11 000--16 000 K. The measured parameters are compared with experimental data taken from the literature.
55 citations
TL;DR: In this paper, an accurate determination of electron density, temperature, and velocity distributions is of primary interest for the characterization of steady-state thermal plasma spray jets based on optical emission spectroscopy including measurements of absolute emission coefficients and Stark broadening.
Abstract: An accurate determination of electron density, temperature, and velocity distributions is of primary interest for the characterization of steady-state thermal plasma spray jets. Our diagnostic capabilities based on optical emission spectroscopy include measurements of absolute emission coefficients and Stark broadening. In addition, enthalpy probe diagnostics has also been used for temperature and velocity measurements. Observation of large discrepancies between temperatures derived from absolute emission coefficients, Stark broadening, and from enthalpy probe measurements indicate that severe deviations from LTE (local thermal equilibrium) exist in various regimes of plasma spray jets. Nonequilibrum characterization of such turbulent thermal plasma jets suggests that diffusion of high-energy electrons into the fringes of plasma jets and deviations from chemical equilibrium due to high velocities in the core of plasma jets and entrainment of cold gas, are the main reasons for these discrepancies. The establishment of a reliable data base, taking these nonequilibrium effects into account, is a prerequisite for meaningful modeling of real plasma jets.
TL;DR: Wave vector selective ac Stark effect of the biexciton state is clearly observed in the steady state regime, implying that the dressed state is established with the coherent mixing of delocalized Bloch states.
Abstract: Wave vector selective ac Stark effect of the ${\mathrm{\ensuremath{\Gamma}}}_{1}$-biexciton state is clearly observed in the steady state regime. The biexciton line splits into two lines with resonant pumping between ${\mathit{Z}}_{3}$ exciton polariton and the biexciton state. From the splitting energy, we have obtained the relevant dipole moment of 4.2e \AA{}. Observed energy of the dressed state coincides with the value derived from the model with strict energy and quasimomentum selection rule. This implies that the dressed state is established with the coherent mixing of delocalized Bloch states.
24 Jul 1994
TL;DR: The femtosecond time-resolved Raman gain spectra of PDA-3BCMU were measured using two pump pulses at 1.97 eV and 1.78 eV as mentioned in this paper.
Abstract: Summary form only given. Ultrafast nonlinear optical responses in photoexcitations in polydiacetylenes (PDAs), and substituted polyacetylene (PA) were investigated. The decay kinetics in PDAs and PTs are discussed in terms of the /sup 1/B/sub u/ exciton, /sup 1/A/sub 9/ exciton, free and self-trapped excitons (STE) and biexciton, while the relaxation in the substituted PA is explained by the confinement effect of soliton-antisoliton pairs. Optical Stark shift in the Raman gain spectrum was observed for a single crystal of polydiacetylene (PDA), PDA-DFMP (2,5-bis(trifluoromethylphenyl) PDA) by using pump-probe spectroscopy apparatus based on a femtosecond CPM laser. The femtosecond time-resolved Raman gain spectra of PDA-3BCMU were measured using two pump pulses at 1.97 eV and 1.78 eV. The spectra at various delay times between -500 fs and 1 ps are explained in terms of the conformational change due to the geometrical relaxation taking place from acetylene-type to butatriene-type configuration associated with the self trapping of free exciton followed, by quasi-thermalization with time constant shorter than 200 fs, which is consistent with the formation time constant of the quasithermal self-trapped exciton being 140 fs determined by the absorption spectral change.
TL;DR: In this article, a new method for measuring electric field magnitude using 2 + 1 photon laser-induced fluorescence of groundstate hydrogen atoms was developed, which was calibrated using H atoms from a distant source flowing through a region of known electric field, and results were presented for field profiles in dc discharges in 0.3 and 1 Torr pure H2.
Abstract: We have developed a new method for measuring electric field magnitude using 2+1 photon laser‐induced fluorescence of ground‐state hydrogen atoms. The atoms are excited to the n=2 level by two 243‐nm photons, then further excited to the n=6 level by one photon at 410 nm and detected by cascaded Hα fluorescence. The electric field magnitude is deduced from the Stark splitting of the n=6 level. The method was calibrated using H atoms from a distant source flowing through a region of known electric field. Results are presented for field profiles in dc discharges in 0.3 and 1 Torr pure H2.
TL;DR: In this paper, high-resolution laser spectroscopy of the Qv(0) (υ=υ←0,J=0← 0) transitions in solid parahydrogen is discussed.
Abstract: Our recent high-resolution laser spectroscopy of theQ
v(0) (υ=υ←0,J=0←0) transitions in solid parahydrogen is discussed. The systems studied include the fundamental vibrational bands of impurity D2 and HD, the first and second overtones of parahydrogen, and the charge-induced spectrum ofγ-ray irradiated parahydrogen. Additionally, Stark and stimulated Raman-gain spectroscopies are applied to the solid. The linewidths are as sharp as 2 MHz HWHM, which is highly unusual for a solid. Our spectra demonstrate a variety of physical phenomena, particularly theΔk = 0 selection rule, as well asJ = 1/J = 0 pair intermolecular interactions.
TL;DR: Using a semiclassical approach, this article calculated electron-, proton-and ionized helium-impact line widths and shifts for 22 Al I multiplets and compared the resulting data with existing experimental and theoretical values.
Abstract: Using a semiclassical approach, we have calculated electron-, proton- and ionized helium-impact line widths and shifts for 22 Al I multiplets. The resulting data have been compared with existing experimental and theoretical values.
Journal Article•
TL;DR: In this paper, Stark broadened hydrogen lines of the Lyman and Balmer series are presented under the conditions of stellar envelopes, based on the Model Microfield Method for both the electronic and ionic contributions to the line shape.
Abstract: Tables of Stark broadened hydrogen lines of the Lyman and Balmer series are presented under the conditions of stellar envelopes. The formalism is based on the Model Microfield Method (MMM) for both the electronic and ionic contributions to the line shape
TL;DR: In this paper, a generalized semi-classical theory of Stark broadening is developed that is free from a shortcoming of the standard semi classical theories of broadening which were intrinsically divergent at small impact parameters.
Abstract: A generalized semi-classical theory of Stark broadening is developed that is free from a shortcoming of the standard semi-classical theories of Stark broadening which were intrinsically divergent at small impact parameters. A convergency of the present theory is achieved by taking into account on equal footing both a “dynamic” splitting of Stark sublevels caused by one of the components of the electron microfield and a quasistatic splitting of Stark sublevels caused by ion microfield (only the latter was allowed for in the standard theories). The presented generalized theory is developed analytically to the same level as the standard theories: it substitutes the “broadening” function C ST ( Z ) of the standard theories by a generalized but still elementary function C ( Z ). The generalized theory embraces the standard theories as one of its limiting cases corresponding to relatively low densities of a plasma. However for dense plasmas the predictions differ: our results demonstrate that the standard theories overestimate an electron impact broadening for high density plasmas.
TL;DR: The motional Stark effect (MSE) diagnostic has been used to obtain accurate measurements of the internal magnetic pitch angle tan−1(BZ/BT) in finite pressure tokamaks as discussed by the authors.
Abstract: The motional Stark effect (MSE) diagnostic has been used to obtain accurate measurements of the internal magnetic pitch angle tan−1(BZ/BT) in finite‐pressure tokamaks. The MSE data, together with external magnetic probe data, are used to reconstruct self‐consistently the equilibrium safety factor (q) profile and, hence, the plasma current density, in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 1, 51 (1986)] and the Princeton Beta Experiment‐Modified (PBX‐M) tokamak [Phys. Fluids B 2, 1271 (1990)]. An efficient computational scheme, based on an inverse coordinate representation of the magnetic field, has been developed to solve the coupled nonlinear equations describing both the magnetohydrodynamic (MHD) equilibrium and the q profile, which best match all the experimental data.
TL;DR: In this paper, a two-ion model to describe the dynamics is given and the gain and losses of the loop are evaluated, and a two ion model is used to describe two-stage process: absorption from the fundamental states of the ions and a looping mechanism.
TL;DR: The ac Stark effect can shift initially nonresonant minibands in semiconductor superlattices into multiphoton resonances and result in strongly enhanced generation of a particular desired harmonic of the driving laser frequency, at isolated values of the amplitude.
Abstract: The ac Stark effect can shift initially nonresonant minibands in semiconductor superlattices into multiphoton resonances. This effect can result in strongly enhanced generation of a particular desired harmonic of the driving laser frequency, at isolated values of the amplitude.
TL;DR: In this paper, a theoretical analysis and experimental studies on the control of the polarization-dependent characteristics of the refractive index change and the absorption change due to the quantum-confined Stark effect in an InGaAs/InP quantum-well structure are presented.
Abstract: We present a theoretical analysis and experimental studies on the control of the polarization-dependent characteristics of the refractive index change and the absorption change due to the quantum-confined Stark effect in an InGaAs/InP quantum-well structure. The polarization dependency which arises from the energy level splitting of heavy-hole and light-hole states in the quantum well can be controlled by inducing an appropriate amount of tensile strain in the quantum well. Measurements were carried out on the polarization dependency of the refractive index change and the absorption change in unstrained, 0.15, 0.3, and 0.45% tensile-strained 11.5-nm-thick InGaAs quantum-well structures through the whole spectral range, i.e., near and below the transition energy. We found that by inducing a 0.3% tensile strain in the 11.5-nm quantum well, the spectral profiles for the transverse electric and the transverse magnetic modes are brought closer to each other, with the peaks of the negative index changes corresponding to both modes occurring at the same wavelength with a slight difference in their absolute values. Moreover, in the long wavelength region, the refractive index change for both modes coincides in the wavelength as well as the absolute value. Based on these results, we have fabricated an absorption modulator and controlled the modulation characteristics with respect to the incident light polarization. >
TL;DR: In this article, the 3ν1+ν3 vibrational overtone spectrum has been recorded at room temperature, 100 K, and approximately 15 K using laser intracavity photoacoustic and molecular beam techniques.
Abstract: Methane’s 3ν1+ν3 vibrational overtone spectrum has been recorded at room temperature, 100 K, and approximately 15 K using laser intracavity photoacoustic and molecular beam techniques. Although rotational congestion renders the room temperature spectrum undecipherable, the 100 K data suggest possible rovibrational assignments that are confirmed in the 15 K spectrum by their individual temperature dependences. Molecular beam Stark spectroscopy is used to unambiguously identify the E symmetry components of the R(2), P(2), and Q(2) transitions. These results indicate the presence of several other bands whose intensities are derived through interactions with the 3ν1+ν3 vibrational overtone transition. Quantitative analysis of these interactions suggests a bright state origin of 11 277.0 cm−1.
TL;DR: In this paper, a modified effective Hamiltonian for degenerate Raman interaction in the far off-resonant case is put forward to include effects of Stark shift, which is more suitable in studying the system than the well known effective Hamiltonians.
Abstract: A modified effective Hamiltonian for degenerate Raman interaction in the far off-resonant case is put forward to include effects of Stark shift. It is found that the modified effective Hamiltonian is more suitable in studying the system than the well known effective Hamiltonian.
TL;DR: In this article, the direction and magnitude of the change in electric dipole moment (Δμ) and in polarizability associated with excitation into S 1 of chromophoric oxacyanine are determined at different concentrations in mixed Langmuir-Blodgett (LB) monolayer films, based on the Stark shift evaluated from the so-called electrochromism.
TL;DR: A new theoretical approach is introduced to describe the virtual excitation of Fermi edge singularities in modulation-doped quantum wells and how ultrashort laser pulses renormalize the effective masses, band-gap transition matrix elements, and interactions of doped semiconductors.
Abstract: We introduce a new theoretical approach to describe the virtual excitation of Fermi edge singularities in modulation-doped quantum wells. We discuss how ultrashort laser pulses renormalize the effective masses, band-gap transition matrix elements, and interactions of doped semiconductors.
TL;DR: In this article, the absorption and emission spectra of Tm3+ ions in gadolinium gallium garnet are reported in order to identify the Stark levels involved in pumped and laser emission processes of this system.
Abstract: The absorption and emission spectra of Tm3+ ions in gadolinium gallium garnet is reported in order to identify the Stark levels involved in pumped and laser emission processes of this system. The analysis of the laser‐excited luminescence from Tm3+ multiplets 1D2, 1G4, 3H4 to the ground manifold 3H6 confirms the assignments of Stark levels, corresponding to D2 symmetry, obtained from absorption and provides additional information. Due to the complex multisite structure, the site‐selective excitation and emission data have been also used. A parametrized crystal‐field calculation, including nine parameters for D2 symmetry, fits the energy‐level diagram satisfactorily.
TL;DR: In this article, the authors measured the sheath electric field in a 13.56MHz parallel-plate helium discharge as a function of voltage, pressure, phase, bias, and electrode drive configuration.
Abstract: Spatially and temporally resolved electric fields in the sheath region of a 13.56‐MHz, parallel‐plate helium discharge have been measured as a function of voltage, pressure, phase, bias, and electrode drive configuration. The electric field was determined from laser‐induced fluorescence measurements of the Stark structure of the n=11 singlet Rydberg manifold. Two‐dimensional maps of the electric field indicate that the field is uniform across a large fraction of the electrode diameter. Measured values of the sheath electric field are compared with the results of a hybrid Boltzmann‐equation–average‐equation simulation.
TL;DR: In this paper, the temperature dependence of the dipole polarizability α(ω, T) of ground state xenon has been measured in the ranges of temperature and wavelength between 293 and 1080 K and 633 and 325 nm, respectively.