Showing papers on "Stark effect published in 1992"
TL;DR: The electric field at the amino terminus of an alpha helix in water has been determined by measuring the shift in the absorption band for a covalently attached, neutral probe molecule with an electric dipole moment difference between the ground and excited electronic states.
Abstract: The strengths of electrostatic interactions in biological molecules are difficult to calculate or predict because they occur in complicated, inhomogeneous environments. The electric field at the amino terminus of an alpha helix in water has been determined by measuring the shift in the absorption band for a covalently attached, neutral probe molecule with an electric dipole moment difference between the ground and excited electronic states (an internal Stark effect). The field at the interface between the helix and the solvent is found to be an order of magnitude stronger than expected from the dielectric properties of bulk water. Furthermore, although the total electric dipole moment of the helix increases with length, the electric field at the amino terminus does not.
258 citations
TL;DR: In this article, the authors reported the first observation of infrared multiphoton dissociation of a strongly bound diatomic molecule, HCl+, by a charge-resonance coupling of electronic states of the molecular ion HCl+.
Abstract: We report the first observation of infrared multiphoton dissociation of a strongly bound diatomic molecule, HCl+. The dissociation is explained by a charge–resonance coupling of electronic states of the molecular ion HCl+. This coupling results in Stark shifts which depend on the internuclear separation thereby changing the molecular bonding. Using a barrier suppression model, we obtain good agreement with the observed dissociation threshold. We show the close relationship between barrier suppression and chaotic dissociation. We also report the first quantitative theoretical and experimental study of infrared multiphoton ionization of a small molecule, HCl. Based on tunnel ionization, we develop a molecular ionization model that incorporates both the large Stark shifts of the molecular ion and the associated large induced dipole moments. The model agrees with the experiment for the multiphoton ionization of HCl. It allows us to derive a general expression for the maximum intensity which can be applied to ...
174 citations
TL;DR: It is found evidence that quantum confinement of electrons in small semiconductor particles causes the nonlinear optical properties in the transparency region to differ markedly from those of bulk semiconductors.
Abstract: We find evidence that quantum confinement of electrons in small semiconductor particles causes the nonlinear optical properties in the transparency region to differ markedly from those of bulk semiconductors. The optical Stark effect makes the dominant contribution to the third-order refractive nonlinearity.
160 citations
TL;DR: Calculations exhibiting the nature of these pendular states for a linear molecule and characteristic features of infrared and microwave spectra which become observable in strong fields are presented.
Abstract: Recent experiments have demonstrated the feasibility of orienting rotationally cooled polar molecules in an electric field. The anisotropy of the Stark effect allows molecules in low rotational states to be trapped in ``pendular states,'' confined to librate over a limited angular range about the field direction. We present calculations exhibiting the nature of these pendular states for a linear molecule and characteristic features of infrared and microwave spectra which become observable in strong fields.
160 citations
TL;DR: Electric-field-modulated reflectivity of three different polydiacetylenes-PTS, poly[2,4-hexadiyne- 1,6-diol-bis (p-toluene sulfonate)]; PFBS and DCHD is analyzed with respect to the underlying mechanism for the observed sensitivity of π-π * transitions to electric fields.
Abstract: Electric-field-modulated reflectivity of three different polydiacetylenes---PTS, poly[2,4-hexadiyne-1,6-diol-bis(p-toluene sulfonate)]; PFBS, poly[2,4-hexadiyne-1,6-diol-bis(p-fluorobenzene sulfonate)]; and DCHD, poly[1,6-di(n-carbazolyl)-2,4-hexadiyne]---has been measured and is analyzed with respect to the underlying mechanism for the observed sensitivity of \ensuremath{\pi}-${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ transitions to electric fields. Excitons of high oscillator strength and their vibronic satellites respond to fields along the polymer backbone by a large quadratic Stark shift, revealing a large polarizability for this direction. About 0.5 eV above the excitonic absorption edge, in a region of relatively low absorption, electroreflectance signals of different origin are observed, which, contrary to the excitonic signals, vary strongly in size among different specimens of the same composition. Line-shape analysis and its dependence on the field strength identify this signal as the Franz-Keldysh effect of free-electron states, the continuum of the excitons, and exclude an assignment to forbidden exciton transitions. The large polarizability of the excitonic states, which results from unusually strong coupling to their continuum, is consistent with a Wannier exciton extending over about ten conjugated bonds and with a small reduced mass of the order 0.1${\mathit{m}}_{0}$. The large binding energy (0.5 eV) and oscillator strength (f\ensuremath{\approxeq}0.6) of the excitons and their extremely strong coupling to continuum states are attributed to the one-dimensional character of the electron states.
147 citations
TL;DR: In this article, spectral lines from terrylene in polyethylene were observed, showing that the molecular symmetry is broken by interactions with the matrix, and that the shifts differ strongly according to the molecule.
146 citations
TL;DR: In this article, the tilt angle of the magnetic field line, a quantity related directly to the distribution of the plasma toroidal current, is deduced from a measurement of the direction of polarization of the Stark components.
Abstract: The motional electric field E=v×B, where v is the velocity and B is the tokamak magnetic field, produces a strong Stark effect in spectral lines emitted by hydrogenic neutral beams. The tilt angle of the magnetic field line, a quantity related directly to the distribution of the plasma toroidal current, is deduced from a measurement of the direction of polarization of the Stark components. In the DIII‐D tokamak, the Balmer‐α line of deuterium emitted by one of the high‐power heating beams is analyzed. A multichord polarimeter measures the magnetic field pitch angle at eight spatial locations covering ∼0.6 of the nominal plasma diameter at the midplane outboard side. The diagnostic offers 2–8‐cm resolution in the major radius and 1‐ms integration time. The accuracy of the measurement of the polarization direction necessary for an adequate reconstruction of the current profiles is obtained with the use of active polarizing elements which produce high‐frequency intensity modulation with an amplitude related ...
146 citations
TL;DR: The quasienergies of a coupled two-level atom and quantized electromagnetic cavity mode with the cavity mode driven by a periodic classical field and shifted Jaynes-Cummings level splittings are calculated.
Abstract: We calculate the quasienergies and steady states of a coupled two-level atom and quantized electromagnetic cavity mode with the cavity mode driven by a periodic classical field. The atom, the cavity mode, and the classical field are all on resonance. The quasienergies give shifted Jaynes-Cummings level splittings. These splittings are reduced by the interaction with the driving field and vanish at a threshold value of the driving field strength. Above the threshold, discrete quasienergies and normalizable steady states do not exist. Below the threshold, for weak driving fields, the steady states are squeezed and displaced Jaynes-Cummings eigenstates. We discuss the relevance of these results to work in cavity quantum electrodynamics.
122 citations
TL;DR: In this article, the authors investigated the quadratic Stark effect on the zero phonon line of the vibrationless S 1 ←S 0 transition of single pentacene molecules embedded in p-terphenyl crystals.
121 citations
TL;DR: Stark effect modulation of the optical absorption spectrum of 40 A diam CdSe nanocrystals show the first excited state of these clusters has a dipole moment of 32±10 D as discussed by the authors.
Abstract: Stark effect modulation of the optical absorption spectrum of 40 A diam CdSe nanocrystals show the first excited state of these clusters has a dipole moment of 32±10 D.
114 citations
TL;DR: In this article, a multichannel motional Stark effect polarimeter system has been installed on the Tokamak Fusion Test Reactor (TFTR), which can measure the magnetic field pitch angle ({gamma}{sub p} = tan{sup {minus}1} (B{sub T})/(B{sup p}) at ten radial locations.
Abstract: Although the q profile plays a key role in theories of instabilities and plasma equilibrium, it has been quite difficult to measure until the recent development of the motional Stark effect (MSE) diagnostic. A multichannel motional Stark effect polarimeter system has recently been installed on the Tokamak Fusion Test Reactor (TFTR). The diagnostic can measure the magnetic field pitch angle ({gamma}{sub p} = tan{sup {minus}1} (B{sub T})/(B{sup p})) at ten radial locations. The doppler shifted D{sub alpha} radiation from a TFTR heating beam is viewed near tangential to the toroidal magnetic field via a re-entrant front surface reflecting mirror. The field of view covers from inboard of the magnetic axis to near the outboard edge of the plasma with a radial spatial resolution of 3--5 cm. A high throughput f/2 optics system results in an uncertainty for {gamma}{sub p} of {approximately}0.1{degrees}--0.2{degrees} with a time resolution of {approximately}5--10 ms. Initial pinch angle profiles from TFTR have been obtained. The MSE data is consistent with the estimated magnetic axis position from external magnetic measurements and the q=1 radius is in good agreement with the inversion radius from the electron cyclotron emission temperature measurements.
TL;DR: The first observation of the resonant Stark tuning of second harmonic generation is reported in this article, where AlInAs/GaInAs asymmetric coupled-well structures are engineered in such a way that certain intersubband transitions (1→2 and 2→3) exhibit a large Stark shift equal to the potential drop between the centers of the wells.
Abstract: The first observation of the resonant Stark tuning of second harmonic generation is reported. Our AlInAs/GaInAs asymmetric coupled‐well structures are engineered in such a way that certain intersubband transitions (1→2 and 2→3) exhibit a large Stark shift equal to the potential drop between the centers of the wells. Thus the second‐order susceptibility ‖χ(2)2ω‖ exhibits a pronounced peak when the bound states are made equally spaced by the application of an electric field and ℏω=ΔE12. A peak ‖χ(2)2ω‖=7.5×10−8 m/V, approximately 200 times the bulk values in InAs and GaAs, has been measured.
TL;DR: In this paper, the permanent electric dipole moments of CaOH and SrOH were measured using the technique of supersonic molecular beam optical Stark spectroscopy, and the results were compared with values from a recent ab initio calculation for CaOH, and with the predictions of a semiempirical electrostatic polarization model.
Abstract: The permanent electric dipole moments of CaOH and SrOH in their X 2Σ+, A 2Π3/2, A 2Π1/2, and B 2Σ+ states have been measured using the technique of supersonic molecular beam optical Stark spectroscopy. For CaOH the values obtained were μ(X 2Σ+)=1.465(61)D, μ(A 2Π1/2)=0.836(32)D, μ(A 2Π3/2)=0.766(24)D, and μ(B 2Σ+)=0.744(84)D, while for SrOH the values were μ(X 2Σ+)=1.900(14)D, μ(A 2Π1/2)=0.590(45)D, μ(A 2Π3/2)=0.424(5)D, and μ(B 2Σ+)=0.396(61)D. The results are compared with values from a recent ab initio calculation for CaOH and with the predictions of a semiempirical electrostatic polarization model.
TL;DR: In this paper, a review of the basic theory of quantitative spectroscopy of atoms and incompletely stripped ions immersed in plasmas, applications to diagnostics and modeling of densities and temperature measurements are discussed, together with magnetic and electric field measurements and determination of anisotropic in the electron distribution function.
Abstract: After a review of the basic theory of quantitative spectroscopy of atoms and incompletely stripped ions immersed in plasmas, applications to diagnostics and modeling of dense plasmas are discussed. Density and temperature measurements are emphasized, together with magnetic and electric‐field measurements and determination of anisotropy in the electron distribution function. The important role of spectral line broadening in soft x‐ray laser research is pointed out. There is a possibility of collisional narrowing of the usual thermal Doppler line profile, although this narrowing may be compensated or over‐compensated by the broadening effects of elastic ion–ion collisions. At very high power levels, the laser line may also be broadened by the laser field via resonant dynamical Stark effects.
TL;DR: In this paper, a linear relationship was established between the polarizability differences of ground and excited state molecules (Δα) from electrochromism measurements and p MW, where p is the slope of the plot of absorption band maxima against the Lorenz-Lorentz function ϕ( n 2 ) = (n 2 − 2)/(n 2 + 2), n is the refractive index of the solvent and MW is the relative molecular weight of the solute.
TL;DR: In this article, an electrically tunable infrared photoconductor is made with GaAs/AlGaAs asymmetric step multiquantum wells, using the linear Stark shift of the intersubband transition.
Abstract: For the first time, an electrically tunable infrared photoconductor is made with GaAs/AlGaAs asymmetric step multiquantum wells, using the linear Stark shift of the intersubband transition. An applied electric field excursion of ±40 kV/cm is sufficient to shift the peak responsivity wavelength from 8.5 to 13.5 μm. The photoresponse tunability is studied by comparing photocurrent and absorption spectra for different applied electric fields.
TL;DR: In this article, it was shown that the superlattice layers of wurtzite CdS/CdSe have been grown on (111)A GaAs substrates by metalorganic chemical vapor deposition and their optical properties studied by photoluminescence spectroscopy.
Abstract: Strained layer superlattices of wurtzite CdS/CdSe have been grown on (111)A GaAs substrates by metalorganic chemical vapor deposition and their optical properties studied by photoluminescence spectroscopy. It is shown that the superlattice layers contain giant strain‐induced piezoelectric fields exceeding 2×108 V m−1. These fields are similar to those reported for (111) orientated III–V superlattices, but an order of magnitude greater. The recombination energies from a series of samples provide evidence for a type II conduction band offset of 0.23±0.10 eV (the electron wells being in the CdS), with the band structure heavily modified by the internal electric fields. In addition, the photoluminescence peak emission energy shows a strong dependence on the excitation power. This is interpreted as further evidence for the effect of internal fields. We conclude that this system shows new effects not previously observed in II–VI compound superlattices. The large band‐gap tunability and the space‐charge effects ...
TL;DR: In this paper, the quantum-confined Stark shift was calculated for eight differently shaped simple Al0.4Ga0.6As/AlxGa1-xAs quantum wells.
Abstract: The quantum-confined Stark shift was calculated, using a numerical method, for eight differently shaped simple Al0.4Ga0.6As/AlxGa1-xAs quantum wells. The dependence of the electron and heavy-hole ground-state interband transition energy on external electric field, quantum well profile and its thickness was investigated. Calculations also include the excitation binding energy, the overlap of the electron and hole wavefunctions and their average spatial separation. A wider well has a larger Stark shift, independent of its shape. An extensive comparison was made of the field response to differently shaped wells having the same zero-field electron ground-state energy (78 meV). The thinnest was a 51 AA wide square well and the thickest a 261 AA asymmetric triangular well. The symmetric and asymmetric triangular wells were found to exhibit the largest Stark shifts but also had a larger reduction of the overlap and exciton binding energy. The square well, on the contrary, had the smallest Stark shift but also smaller variation of the overlap and exciton binding energy. Other wells exhibited characteristics between these two extreme cases.
TL;DR: In this article, the Stark splittings and shifts of many rotational lines in the 810 band of the A 1B3u←X 1Ag transition of naphthalene-H8 and C 10D8 were measured in a static homogeneous electric field.
Abstract: Laser Stark spectroscopy has been performed on C10H8 and C10D8 molecules in a collimated, seeded supersonic beam. The Stark splittings and shifts of many rotational lines in the 810 band of the A 1B3u←X 1Ag transition of naphthalene–H8 and –D8 could be measured in a static homogeneous electric field. The determined polarizability anisotropies of the A 1B3u state of C10H8 are P’aa−Pbb=9.9(2) A3 and P’bb−Pcc=6.4(2) A3, whereas the X 1Ag ground state results are P‘aa−P‘bb=6.2(2) A3 and P‘bb−P‘cc=7.2(2) A3. The change of the average polarizability between these states was determined to ΔP=P’−P‘=1.6(1) A3. The corresponding values of C10D8 were found to be P’aa−P’bb=10.1(2) A3, P’bb−P’cc=6.2(2) A3, P‘aa−P‘bb=6.1(2) A3, P‘bb−P‘cc=7.3(2) A3 and ΔP=P’−P‘=1.6(1) A3.
TL;DR: In this article, the spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy.
Abstract: The spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy. The electron density was derived from Stark broadening and shift of spectral lines. It was found that the radial gradient of the electron density is much smaller than the gradient of the atomic number density of atoms ablated by the laser into the plasma. The almost homogeneous plasma conditions in the centre of the microplasmas are essential for quantitative element analysis of solid samples by laser ablation. On the other hand, because of the homogeneous conditions microplasmas are excellent sources for measurements of reliable Stark broadening and shift parameters of atomic and ionic spectral lines of all elements which can be ablated by lasers from solid samples.
TL;DR: In this paper, a new set of wavenumbers for the Stimulated Raman Spectrum (SRS) of the ν 1 band of 12CH4 is presented using the Infrared (IR) absorption spectrum of the P10 component of the same molecule as a standard.
Abstract: A new set of wavenumbers for the Stimulated Raman Spectrum (SRS) of the ν 1 band of 12CH4 is presented using the Infrared (IR) absorption spectrum of the P10 component of ν 3 of the same molecule as a wavenumbers standard. An estimation of the Stark shift due to the pump laser field is experimentally deduced what allows to extrapolate the measured wavenumbers to zero field amplitude. A careful discussion about the main possible error sources and how to cope with them is also included.The absolute accuracy of the wavenumbers set presented here is believed to be at least one order of magnitude better as compared with previous measurement.
TL;DR: The biaxial response of photoluminescence to electric fields in GaAs quantum-well structures is reported on and the field dependence of the anisotropy is unusual in that it decreases with increasing field.
Abstract: We report on the biaxial response of photoluminescence to electric fields in GaAs quantum-well structures. For fields along [001], emission due to nominally forbidden excitons exhibits substantial differences between [110] and [11\ifmmode\bar\else\textasciimacron\fi{}0] polarizations. Transitions which are allowed within the envelope-function formalism show no noticeable anisotropy. In terms of symmetry, our observations relate to the linear electro-optic (Pockels) effect. The field dependence of the anisotropy is unusual in that it decreases with increasing field. Results can be qualitatively accounted for by perturbation analyses.
TL;DR: In this article, the authors examined regularities in plasma-produced line shifts (Stark shifts) by a comprehensive analysis of literature data and showed conclusively that the measured data exhibit these predicted regularities.
Abstract: We have examined regularities in plasma-produced line shifts (Stark shifts) by a comprehensive analysis of literature data. Since the shifts are the result of atomic collision processes, regularities are expected from general atomic structure considerations. Specifically, systematic behavior should occur for spectral series and for corresponding transitions in homologous atoms and isoelectronic ions. Also, Stark shifts should be similar for lines within multiplets and, to a lesser degree, within supermultiplets and transition arrays. Numerous examples show conclusively that the measured data exhibit these predicted regularities. When pronounced irregularities occur, they are readily explainable in terms of special circumstances in the atomic structure.
TL;DR: In this article, the experimental results did not show a scaling with ${\mathit{Z}}^{\mathrm{\ensuremath{-}}2}$, where Z is the spectroscopic charge number, which was expected from theoretical calculations in the electron-impact approximation.
Abstract: Experimental Stark widths of the 3s $^{2}3\mathrm{p}$ $^{2}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ transitions in the Li-like ions C iv, N v, O vi, and Ne viii are reported. The measurements were performed for a set of plasma parameters so that the density and temperature behavior of the Stark widths could be observed and compared with calculations. The experimental results did not show a scaling with ${\mathit{Z}}^{\mathrm{\ensuremath{-}}2}$, where Z is the spectroscopic charge number, which is expected from theoretical calculations in the electron-impact approximation. Furthermore, deviations from linear scaling appear for Z=8.
TL;DR: In this article, a general theory is presented for the ac Stark effect in a diatomic molecule undergoing a multiphoton transition, where the sum of the photon energies is resonant with an allowed transition, a splitting of the line is observed (Autler-Townes effect).
Abstract: The (2+2) resonance‐enhanced multiphoton ionization (REMPI) of N2 via the a 1Πg(v=1,J) levels shows a strong dependence on the polarization of the laser beam causing this process. This behavior is attributed to the ac Stark effect produced by the near resonance of the N2 o31Πu(v=0,J) levels with the sum of the first three photons. The multiphoton transitions are broadened and asymmetric in appearance; one level is even split. The line profiles change markedly as the polarization of the laser beam is varied from linear to circular. A general theory is presented for the ac Stark effect in a diatomic molecule undergoing a multiphoton transition. When the sum of the photon energies is resonant with an allowed transition, a splitting of the line is observed (Autler–Townes effect). Off resonance, the magnetic sublevels are shifted by different amounts, causing the line profile to be broadened and distorted. This theoretical treatment is able to explain in a satisfactory manner the observed behavior of (2+2) REMPI of N2 via the a 1Πg–X 1Σ+g transition and the two‐photon laser‐induced fluorescence of CO via the A 1Π–X 1Σ+ transition.
TL;DR: In this paper, a tunable diode laser was used as a light source for line-of-sight absorption measurements in an atmospheric pressure plasma, and the lineshapes were fit to Voigt profiles, allowing inference of both Stark broadening and shift which, in turn, specifies the electron number density and the kinetic temperature.
Abstract: A tunable diode laser was used as a light source for line-of-sight absorption measurements in an atmospheric pressure plasma. Spectrally-resolved argon absorption lineshapes at 8115 and 8104 A, corresponding to the 4s3P2→4p3D3 and 4s3P1→4p3D1 transitions of argon, were recorded in a 1 kW, 27 MHz inductively-coupled argon plasma 11 mm downstream from the load coil. Lineshapes were fit to Voigt profiles, allowing inference of both Stark broadening and shift which, in turn, specifies the electron number density and the kinetic temperature. A population temperature for each of the probed levels was determined from frequency-integrated line intensities. The difference between ionization temperatures, determined from measured electron number-density values assuming Saha equilibrium between atoms and ions, and population temperatures suggests the presence of a suprathermal electron number density. The methods presented here provide important new capabilities for plasma diagnostics.
TL;DR: In this paper, the electronic energy levels of C 60 thin films are reviewed, and the electroabsorption spectra are discussed in terms of the Stark effect on energy levels, including A g, H g and T u symmetries.
TL;DR: These results consist of the first identification, in a high intensity short-pulse photoelectron spectrum, of low-lying states of argon with an ac Stark shift significantly different from the ponderomotive energy.
Abstract: We report experimental results which imply that observed peaks in the short-pulse photoelectron spectrum of atoms in high fields result only from a resonant enhancement of the multiphonon ionization rate at the peak of the laser pulse, rather than a two-step process of real population transfer and subsequent single-photon ionization. These results consist of the first identification, in a high intensity (g${10}^{13}$ W/${\mathrm{cm}}^{2}$) short-pulse photoelectron spectrum, of low-lying states of argon with an ac Stark shift significantly different from the ponderomotive energy.