Showing papers on "Stark effect published in 1976"

Doppler-Free Laser Polarization Spectroscopy

Abstract: We have demonstrated a sensitive new method of Doppler-free spectroscopy, monitoring the nonlinear interaction of two monochromatic laser beams in an absorbing gas via changes in light polarization. The signal-to-background ratio can greatly surpass that of saturated absorption. Polarization spectra of the hydrogen Balmer-$\ensuremath{\beta}$ line, recorded with a cw dye laser, reveal the Stark splitting of single fine-structure components in a Wood discharge.

A quantum-mechanical master equation treatment of the dynamical Stark effect

Abstract: The description begins with an operator master equation for the atom plus incident field. Reduced atomic matrix elements are derived for arbitrary field strengths. First- and second-order correlation functions in the scattered field are also obtained and discussed in relation to the scattered spectrum and intensity-fluctuation measurements. This formalism has the appealing feature that all information is readily available from the one set of four coupled equations. The deficiencies in both the one-photon approximation and the semiclassical perspective are established in a natural and transparent fashion.

A critical review of the Stark widths and shifts of spectral lines from non‐hydrogenic atoms

Abstract: A critical review of all available data on the Stark broadening and shifts of spectral lines of neutral elements has been undertaken. Over 200 papers compiled by the NBS Data Center on Atomic Line Shapes and Shifts have been evaluated, and of these, 68 were chosen as having reviewable data. Only those papers with properly determined critical factors, such as electron density, temperature, spatial homogeneity, optical depth, and instrument function deconvolution, were selected.

Proposal for the measurement of the resonant Stark effect by photon correlation techniques

Abstract: The second-order correlation function for light scattered at resonance from a two-level atom is calculated The measurement of intensity correlations employing either homodyne or heterodyne techniques provides a novel approach for the extraction of linewidth and splitting frequencies

Experimental Stark widths and shifts for non‐hydrogenic spectral lines of ionized atoms

Abstract: A critical review of all available data on the Stark widths and shifts for lines of non‐hydrogenic ionized spectra has been carried out. The relevant literature compiled by the NBS Data Center on Atomic Line Shapes and Shifts was critically evaluated, and from this evaluation 54 papers were found to satisfy all requirements and thus selected for this review. The most important factors determining the quality of plasma sources, diagnostic techniques, and line profile and shift determinations are discussed in detail in the first part of this review. In the second part the data tables containing the selected experimental Stark broadening parameters are presented. The data are arranged according to spectra and elements, and these are presented in alphabetical order. The accuracy of the experimental data is estimated on the basis of guidelines developed during the review, and comparisons with theoretical results are made whenever possible.

Experimental Stark Widths and Shifts for Non-Hydrogenic Spectral Lines of Ionized Atoms (A Critical Review and Tabulation of Selected Data),

Abstract: : A critical review of all available data on the Stark widths and shifts for lines of non-hydrogenic ionized spectra has been carried out. The relevant literature compiled by the NBS Data Center on Atomic Line Shapes and Shifts was critically evaluated, and from this evaluation 54 papers were found to satisfy all requirements and thus selected for this review. The most important factors determining the quality of plasma sources, diagnostic techniques, and line profile and shift determinations are discussed in detail in the first part of this review. In the second part the data tables containing the selected experimental Stark broadening parameters are presented. The data are arranged according to spectra and elements, and these are presented in alphabetical order. The accuracy of the experimental data is estimated on the basis of guidelines developed during the review, and comparisons with theoretical results are made whenever possible. (Author)

Enhancement of dielectronic recombination by plasma electric microfields

Abstract: A description is presented of an application of techniques from Stark-broadening theory considered by Griem (1974) to the computation of dielectronic recombination rated for multiply charged Fe ions under the influence of plasma electric microfields. Attention is given to a dielectronic recombination process for which the effects of surrounding charged particles have been found to be important at surprisingly low densities.

Laser‐induced rate processes in gases: Dynamics of polyatomic systems

Abstract: A model is proposed to describe the collision‐free dynamics of a polyatomic molecule driven by an intense laser field. The evolution in time of stable and quasistable (chemically reactive) energy level populations driven on and off resonance are given, and analytic estimates are derived for the effects of dynamic power broadening (a–c Stark effect), mode and level degeneracies, and rapid unimolecular decay on the efficiency of laser pumping.

Birefringence arising from the reorientation of the polarizability anisotropy of molecules in collisionless gases

Abstract: The refractive index change in a collisionless gas is evaluated from the Stark shifts of the rotational energy levels that arise from the polarizability anisotropy. For the limit of an extremely short-duration excitation, a multilevel coherent effect resulted in delayed refractive index bursts. Both stationary and transient responses of this birefringence to an optical field were considered for symmetric top molecules, with particular emphasis on the special case of linear molecules.

Spectral Resolution of Near-Resonant Rayleigh Scattering and Collision-Induced Resonance Fluorescence

Abstract: Light scattered from strontium vapor near its 460.73-nm ($^{1}{P}_{1}^{\ensuremath{\circ}}\ensuremath{-}^{1}S_{0}$) resonance transition was resolved into its three spectral components: Rayleigh scattering, collision-induced fluorescence, and three-photon scattering. The saturation behavior of the central (Rayleigh) component and the intensity and ac Stark shift of the three-photon component were studied as a function of detuning and laser intensity. Good agreement is obtained with theoretical predictions.

Stark broadening in hot, dense laser-produced plasmas

Abstract: Broadened Lyman-$\ensuremath{\alpha}$ x-ray lines from neon x and argon XVIII radiators, which are immersed in a hot, dense deuterium or deuterium-tritium plasma, are discussed. In particular, these lines are analyzed for several temperature-density cases, characteristic of laser-produced plasmas; special attention is paid to the relative importance of ion, electron, and Doppler effects.

Unidirectional saturation spectroscopy, II

Abstract: The general probe absorption coefficient derived in Part I is specialized to homogeneous- and inhomogeneous-broadening limits and illustrated as the dipole lifetime is increased from 0 to values comparable to the level lifetimes. This progression reveals the relation between pulsation dips of the short-dipole lifetime limit and the dynamic Stark effect in general. Interpretations of the coherent interactions involved are given in terms of modulator and Raman effects and of dressed atoms. The single-probe unidirectional pulsation dip is shown to be a special case of the grating dip in which the fringe spacing becomes infinite. Analogies with three-level systems are given in which both two and three-level cases are seen to obey an “equal-area theorem”, and to involve level crossing. Some comparison is made with corresponding spectroscopy in which spontaneous emission provides the probe radiation.

Photon‐assisted nonresonant charge exchange: A simple molecular model

Abstract: A simple two‐state molecular theory for calculating the cross section for the photon‐assisted charge‐exchange collision process A++B+hν→A*+B+ is described. The semiclassical impact‐parameter method is applied to such collisions and for simplicity the nuclear trajectory is assumed to be rectilinear. Ignoring the Stark broadening and trajectory distortion of the molecular levels the exact solution of the resulting coupled charge‐transfer equations is obtained. A simple model of the required molecular transition moment is discussed and applied to obtain numerical results. The cross section, averaged over the molecular orientation, as a function of the applied field intensity and relative nuclear translational energy is determined. Using parameters characteristic of an atomic system the cross sections for photon‐assisted charge transfer are presented for intensities of 109–1011 W cm−2 and relative nuclear energies varying from 10 to 1000 eV. Our results demonstrate that considerable enhancement of the charge‐exchange cross section may be possible with the moderate field intensities presently available. 148

Photon-assisted nonresonant charge exchange: A simple molecular model. [Cross sections, 10 to 1000 eV]

Abstract: A simple two-state molecular theory for calculating the cross section for the photon-assisted charge-exchange collision process A/sup +/+B+h..nu -->..A*+B/sup +/ is described. The semiclassical impact-parameter method is applied to such collisions and for simplicity the nuclear trajectory is assumed to be rectilinear. Ignoring the Stark broadening and trajectory distortion of the molecular levels the exact solution of the resulting coupled charge-transfer equations is obtained. A simple model of the required molecular transition moment is discussed and applied to obtain numerical results. The cross section, averaged over the molecular orientation, as a function of the applied field intensity and relative nuclear translational energy is determined. Using parameters characteristic of an atomic system the cross sections for photon-assisted charge transfer are presented for intensities of 10/sup 9/--10/sup 11/ W cm/sup -2/ and relative nuclear energies varying from 10 to 1000 eV. Our results demonstrate that considerable enhancement of the charge-exchange cross section may be possible with the moderate field intensities presently available. 148 (AIP)

Full anisotropy of stark effect on b-1(2u)]-a-1(g) electronic-transitions of tetracene and pentacene in a para-terphenyl host crystal

Abstract: The results of a low temperature Stark-effect study on the visible short axis polarized singlet transitions of tetracene and pentacene are presented and discussed. The full anisotropy of the Stark effect could be obtained reliably only by using bipolar electric field modulation together with an optical multichannel detection system. This system is also briefly described in this paper. Using the anisotropic Lorentz approximation the difference polarizability tensor components are found to be: for tetracene ΔαLL = 29 ± 3 A3, ΔαMM = 25 ± 4 A3, ΔαNN = 5 ± 5 A3; and for pentacene ΔαLL = 53 ± 4 A3, ΔαMM = 90 ± 8 A3, and ΔαNN = -11 ± 9 A3. The paper emphasizes that these numbers, due to the inherent approximations of the Lorentz approximation, should be handled with great caution.

On the validity of the model microfield method as applied to Stark broadening of neutral lines

Abstract: Certain features of the interactions between atoms and fluctuating microfields are discussed, emphasizing those statistical properties of the microfield which play an important role in Stark broadening. A model microfield is constructed incorporating the most relevant features, and it is shown that the model microfield theory constitutes a completely unified treatment and is a powerful tool for testing certain standard approximations.

Excitation cross sections for 3s, 3p and 3d sublevels of atomic hydrogen split from simple molecules by high-energy electron impact

Abstract: Relative cross sections for the excitation of the 3s, 3p and 3d sublevels of atomic hydrogen were determined in the case of dissociative excitation of H 2 , HCl, H 2 O, NH 3 and CH 4 molecules by impact of 1000 and 2000 eV electrons. For this purpose the intensity as well as the polarization of the emitted Balmer-α radiation has been measured as a function of an applied homogeneous electric field. Using the theory of the Stark level mixing for H-atoms, it was derived from these data that within the experimental error only the 3s and 3d states of H were excited.

Microwave spectrum of formyl chloride

Abstract: The unstable product found in the chlorination of formic acid has been identified as formyl chloride by microwave spectroscopy. The lifetime of this molecule was about 3 min in the waveguide cell at dry ice temperature. The rotational constants of seven isotopic species have been measured and analyzed, yielding moments of inertia from which a molecular structure was calculated. The bond lengths found are (in A)C–Cl=1.760, C–O=1.188, and C–H= 1.096. The bond angles are HCCl=109°58′ and HCO=126°29′. Planarity was established by the analysis of the inertia defects. The nuclear quadrupole coupling constants in the C–Cl bond‐axis system are χzz= −59.8 MHz and η=−0.30. From the analysis of the Stark effect under a weak electric field condition, the dipole moment has been determined as ‖μa‖=0.3±0.2 D, ‖μb‖=1.6±0.2 D, and ‖μtotal‖ = 1.6±0.2 D.

Theory of Optical-Microwave Double Resonance I. Fundamentals and Double Resonance of Microwave Detection

Abstract: The effect of optical pumping on the lineshapes and the peak values of microwave absorption line is calculated by a density matrix method in the Doppler limit approximation. The calculated double resonance signal consists of two terms. One is proportional to the unperturbed population difference of the optical transition and has a Lorentzian lineshape at weak microwave saturation. In this term the two-photon processes cause broadening of the line. The other is proportional to the population difference of the microwave transition and gives the higher-order dynamic Stark effect. At moderate optical saturation the former term is much greater than the latter. At strong optical saturation the latter term becomes noticeable and lineshape anomaly occurs. The peak values of the double resonance signals are also calculated and compared with an experimental result.

Far ir laser with metal-dielectric waveguide to observe the Stark effect.

Abstract: We report the operation of a hollow rectangular combination metal-dielectric waveguide (Fig. 1) used as a guide for a far infrared (FIR) optically pumped gas laser. A similar guide was recently proposed by Garmire et al. as a low loss curved guide for transmission of power. The first optically pumped waveguide FIR laser using a cylindrical waveguide, was reported by Hodges and Hartwick. Our purpose for constructing this type of combination guide was to have an efficient guide for studying the Stark effect on the operation of the FIR laser. The FIR waveguide resonator consists of a rectangular waveguide in addition to the end mirrors. The wider walls of the guide are constructed of two common plate glass strips 3.2 cm wide by 79 cm long. These strips are coated with aluminum to apply electric fields to the gas to induce the Stark effect. An uncoated section of 1-cm length was left at each end of the strips to provide electrical insulation from the gold-plated end mirrors. The narrower sidewalls of Teflon aid in the confinement of the CO2 pump and FIR laser radiation, thereby increasing the gain over a parallel plate waveguide. The combined walls form a 2.5-cm by 1.3-cm rectangular waveguide. One mirror is directly at the end of the guide, and the second mirror is located a few millimeters from the other end and can be adjusted to tune the FIR laser. The pump is a cw CO2 laser from which several watts are coupled into the cavity to pump CH3CN or CH3OH. One mirror has either a 1.9-mm coupling hole or a 3.5-mm coupling hole in an output configuration similar to that used in Ref. 3. The FIR power output, measured with a Golay detector, is comparable with that obtained with a metal cylindrical tube waveguide laser. The wavelengths are measured by a metal mesh Fabry-Perot interferometer. The fields for the guide modes should be essentially transverse for dimensions of the guide much larger than the wavelength. The lowest loss modes occur for the E field polarized parallel to the metal walls. Using Eq. (13) from Garmire et al. for the loss of the lowest order mode, we calculate a theoretical loss coefficient of 6.4 × 10 -4 m 1 for the 100-μm wavelength, increasing to 1 × 10 -2 m 1 for 400-μm wavelength. We can compare this with the mode loss for the E field perpendicular to the metal walls by calculating the losses in each set of walls in analogy to Garmire's method. This results in a field loss for metal walls of conductivity σ and dielectric sidewalls of refractive index v:

Application of the model microfield method to Stark profiles of overlapping and isolated neutral lines

Abstract: Describes a number of analytical and numerical calculations related to the model microfield method applied to Stark broadening (in particular, treatment of strong collisions and angular averages). This method is used for several types of profile: He I overlapping lines, Li I and Mg I resonance lines and Li I and O I non-resonance lines. For each of these, various approximations are discussed and the profiles are compared to those obtained from other theories and to experimental results. In particular, it is shown that the forbidden components cannot be obtained correctly using the usual approximation in which the electronic broadening is calculated independently of the ionic microfield.

Two-photon spectroscopy. II. Effects of residual Doppler broadening

Abstract: For pt.I see ibid., vol.8, p.1795 (1975) where the theory of Doppler-free two-photon transitions was discussed for the case of one single laser frequency. Here, the effects of two different frequencies are considered. When the residual Doppler width of the two-photon transition is less than the natural linewidth, the previous results are essentially regained. For large residual Doppler shifts, the absorption profile is a power-broadened Lorentzian if the frequency of the probe field is larger than the frequency of the strong field. In the opposite case, the absorption peak splits because of the AC Stark effect. The high-intensity distortions are minimized when equal frequencies can be used. Power-dependent shifts do not ordinarily occur with a resonantly tuned intermediate level. Some modifications of the spectra are introduced by phase-disturbing collisions.

Experimental investigation of Stark broadening and plasma polarization shift of ionized helium resonance lines

Abstract: Stark broadening and shift measurements were performed on ionized helium resonance lines from a fully ionized helium plasma in a low-inductance electromagnetic T tube. Both time-integrated photographic and time-resolved photoelectric measurements of the lines were performed with a grazing incidence spectrometer. Electron density and temperature were determined from the widths of the He II 4686-A and the He I 5876-A lines and the He II 4686-A line to continuum ratio, respectively. It was found that all ionized helium resonance lines were emitted optically thick by a homogeneous plasma slab and self-reversed by a thin cooler boundary layer. Marked blue shifts of 0.07 plus or minus 0.05 A which may be due to plasma polarization were noted.