Time-dependent analysis of nonstationary effects in velocity-selective optical pumping is performed with a four-level model for weak light intensities. No phenomenological relaxation constants are introduced and the nonstationary effects are obtained as the consequence of averaging the time evolution of individual atoms in a vapor phase moving in the light fields when typical pumping times are comparable with the finite laser-beam transit times. Under appropriate conditions strong deformation of the population distribution of the long-lived lower state occurs, which in the case of polarization spectroscopy is responsible for the appearance of a dip (possibly narrower than the homogeneous linewidth) in the center of a Doppler-free resonance. The theoretical results are in a good qualitative agreement with the recent experimental observations.

Translational energy-gain spectroscopy is used to determine the final-state (nl) populations following single-electron capture by ${\mathrm{Ar}}^{\mathrm{q}+}$ (q=4–8) and ${\mathrm{Ne}}^{\mathrm{q}+}$ (q=4–7) projectiles in atomic and molecular deuterium targets at an energy of 545q eV. The importance of kinematics in analyzing these systems is discussed. The final-state populations are found to be very sensitive to the energy-level structure of the collision system. The results are interpreted in terms of a ‘‘reaction window’’ in the energy gain which is calculated using a multichannel Landau-Zener model.

Photoionization of helium and neon to excited satellite states, ${\mathrm{He}}^{+}$ nl and ${\mathrm{Ne}}^{+}$ 1$s^2$2$s^2$2$p^4$nl, was studied with synchrotron radiation and threshold electron analysis. Photoelectron satellites have been directly measured at threshold for the first time to our knowledge. The relative satellite cross sections were determined over the kinetic energy range from 0 to 1 eV. The angular distributions were also evaluated close to threshold. Strong correlation effects were observed in two cases. For He near threshold, the angular-distribution asymmetry parameter β is near zero for the n=2 satellite and is increasingly negative for the higher-n satellites, in agreement with the theoretical prediction of Greene. In the threshold photoelectron spectrum of Ne, many final states are present, some with quartet spin multiplicity and others with high-L values.

The close-coupled theory of collisions in a radiation field is used to calculate the absorption profile for the Sr ${}_{}{}^1{}_{}{}^{}\leftarrow _{}^1{}_{}{}^{}$S resonance line broadened by collisions with Ar. The calculations predict the polarization ratios of Sr ${}_{}{}^1{}_{}{}^{}\mathrm{P}$ fluorescence following line wing excitation by either linear or circular polarized light. Ab initio calculations were used to obtain the ground and excited SrAr molecular-potential curves, which were adjusted to give improved agreement with experiment. The radiative-scattering theory gives a unified description of the absorption coefficient and polarization redistribution from the small detuning impact limit region to the far spectral wings. The cross sections for elastic and inelastic depolarizing collisions of Sr ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$+Ar were also calculated. The calculated absorption coefficient, impact-broadening rate, linear- and circular-polarization ratios, and depolarization rate coefficients are for the most part in good agreement with experiment.

New data on odd-parity autoionization in xenon have provided an opportunity to apply multichannel-quantum-defect theory (MQDT) to the J=0 spectra. This analysis complements the many studies of the J=1 spectra. Nine bound and seven autoionizing levels were analyzed. The resulting MQDT parameters are able to reproduce the measured energy levels with an rms error of 0.33 ${\mathrm{cm}}^{\mathrm{-}1}$, and predictions of autoionization rates are in good agreement with observed linewidths. The position and width of the lowest J=0 autoionization resonance, the 8s’${\left[\mathrm{}\right(1/2\left)\mathrm{}\right]}_0$ level, are predicted.

L-shell x-ray production cross sections by 0.25–2.5-MeV ${}_2{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ ions in ${}_{28}{}^{}{}_{}{}^{}\mathrm{Ni}$, ${}_{29}{}^{}{}_{}{}^{}\mathrm{Cu}$, ${}_{32}{}^{}{}_{}{}^{}\mathrm{Ge}$, ${}_{33}{}^{}{}_{}{}^{}\mathrm{As}$, ${}_{37}{}^{}{}_{}{}^{}\mathrm{Rb}$, ${}_{38}{}^{}{}_{}{}^{}\mathrm{Sr}$, ${}_{39}{}^{}{}_{}{}^{}\mathrm{Y}$, ${}_{40}{}^{}{}_{}{}^{}\mathrm{Zr}$, and ${}_{46}{}^{}{}_{}{}^{}\mathrm{Pd}$ are reported. The data are compared to the first Born approximation and the ECPSSR theory that accounts for the projectile energy loss (E) and Coulomb deflection (C) as well as the perturbed-stationary-state (PSS) and relativistic (R) effects in the treatment of the target L-shell electron. Surprisingly, the first Born approximation appears to converge to the data while the ECPSSR predictions underestimate them in the low-velocity limit. This is explained as the result of improper use of single-hole fluorescence yields. A heuristic formula is proposed to account for multiple ionizations in terms of a classical probability for these phenomena and, after it is applied, the ECPSSR theory of L-shell ionization is found to be in good agreement with the data.

Experiments have shown the novel combination of laser optical pumping and velocity-changing collisions (between active- and buffer-gas atoms) to be very effective in producing vapors with high atomic or nuclear polarizations. This paper presents a theory which has proven successful in analyzing these experiments. The theory predicts the amount of polarization attainable for particular experimental conditions and establishes the general criteria for optimum polarization. The theory is based on sets of coupled rate equations, which contain terms describing the pumping process (i.e., stimulated absorption or emission), radiative branching, relaxation, and velocity-changing collisions. The collision terms are written in the strong-collision approximation, which assumes that a single collision, on average, thermalizes the velocity distribution. Expressions are derived for the polarization and level populations.

Using a new approach to the problem of the interaction of a composite system with a quantized radiation field, an expression for the two-photon amplitude of a composite system is derived in its center-of-mass frame, correct to order $v^2$/$c^2$. In the expression for the amplitude there are terms which depend on the recoil of the composite system due to the emission of the photons. These terms which are of order $v^2$/$c^2$ compared to the nonrelativistic terms were neglected in the previous relativistic treatments of the problem. We also show that the amplitude is relativistically invariant to order $v^2$/$c^2$, when viewed from another Lorentz frame. We have used the relativistic center-of-mass and internal variables of Krajcik and Foldy [R. A. Krajcik and L. L. Foldy, Phys. Rev. D 10, 1777 (1974)] throughout the treatment.

Rotationally resolved spectra of kinetic energy releases ɛ in predissociations of ${\mathrm{H}}_2$, after dissociative charge exchange of ${\mathrm{H}}_2$${\mathrm{}}^{+}$ with Cs atoms, are obtained. The experiments are performed with natural and with pure parahydrogen. The predissociations with ɛ<1.9 eV constitute less than 5% of the total amount of dissociations to H?‖H at a beam energy of 5 keV. All strong rotational peaks observed could be attributed to n=3 Rydberg states which predissociate to H(1s)+H(2l). Vibrational-rotational series are observed of the d ${\mathrm{}}^3$${\Pi }_u^{+}$, D ${}^1$${\Pi }_u^{+}$, and J ${}^1$${\Delta }_g^{+}$ states. Predissociation by barrier tunneling is reported of v=4 levels of the h${\mathrm{}}^3$${\Sigma }_g^{+}$ state and of v=4 and 5 levels of the i ${\mathrm{}}^3$${\Pi }_g$ state. Selectivity of the charge-exchange process for different n=3 states, or even for different parity states, is concluded.

Fast-beam photofragment spectroscopy has been applied to study the photodissociation of metastable ${\mathrm{H}}_2$ molecules in the c ${}^3$${\Pi }_u^{\mathrm{-}}$ state, formed by charge exchange of ${\mathrm{H}}_2$${\mathrm{}}^{+}$ with Cs vapor. Transitions leading to radiatively dissociated or predissociated levels of the g, h, i, and j triplet gerade states of ${\mathrm{H}}_2$ are observed. The decay mechanisms, level positions, and, in the case of predissociations, the lifetimes are established for (ro-)vibrational levels (v≥4). The transitions to v≥5 levels of the j ${\mathrm{}}^3$${\Delta }_g$ state appear as asymmetric peaks with widths of around 50 ${\mathrm{cm}}^{\mathrm{-}1}$ (N=2). A calculation of the rotational coupling of the j state to the vibrational continuum of the i ${\mathrm{}}^3$${\Pi }_g$ state confirms this very rapid predissociation (τ≃${10}^{\mathrm{-}13}$ s). For v=4 of the j state, which couples to the continuum via the quasibound v=5 level of the i state, a relatively slow predissociation (τ≃${10}^{\mathrm{-}8}$ s) is observed.

Quenching of the metastable 2s state of the ${\mathrm{He}}_{\mathrm{\mu }}$${\mathrm{}}^{+}$ atom in helium gas is discussed. The first part of the discussion, which is devoted entirely to processes occurring after the ${\mathrm{He}}_{\mathrm{\mu }}$${\mathrm{}}^{+}$ has become bound to one or more ordinary helium atoms, is based partly on Cohen’s calculations of rates of vibrational quenching and partly on estimates obtained in the present paper of rates of Burbidge–de Borde quenching and Ruderman quenching. It is concluded that Burbidge–de Borde quenching or Ruderman quenching, or both, are likely to be more effective than Cohen quenching if the vibrational level of the bound system is low. A recent experiment by von Arb et al. is then analyzed in the light of this conclusion. The analysis is based on the reported absence, or near absence, of Auger electrons accompanying 2s quenching. While it is agreed that the Cohen mechanism occurring in the molecular ion ${\mathrm{HeHe}}_{\mathrm{\mu }}$${\mathrm{}}^{+}$ remains the most likely explanation of the experiment, it is concluded that the quenching occurs in comparatively high levels. It is then argued that this conclusion is in accord with some theoretical investigations of three-body association reactions and also with some elementary considerations regarding the relaxation of highly excited diatomic molecules, and it is further concluded that the quenching is most likely to occur in states with very low rotational quantum number and vibrational quantum number 8≤v≤14.

The results of ab initio calculations of photodetachment of ${\mathrm{K}}^{\mathrm{-}}$ are presented and compared with experimental measurements. The energy region studied is from threshold to the vicinity of the first excited state of neutral potassium. The calculations are essentially nonrelativistic in nature, but the fine structure in the first excited state (a doublet) is resolved in the calculations by a three-step process: a transformation of dynamical variables to a form that is relatively independent of energy over an energy range comparable to the splitting, an algebraic transformation from LS to jj coupling, and finally by kinematic corrections for the splitting. The initial transformation, a simple phase rotation, was determined empirically, but is shown to be consistent with a formal correction for the effects of long-range polarization forces in electron scattering by potassium near the 4p ${\mathrm{}}^2$$P^o$ threshold.

Spontaneous Raman spectroscopy is used as a tool for studying the vibrational energy distribution of collisionless infrared-multiphoton-excited ${\mathrm{SF}}_6$. A collisionless increase in Stokes and anti-Stokes signals from the strong Raman-active ${\nu }_1$ mode is observed after infrared-multiphoton excitation by a high-power 500-ps ${\mathrm{CO}}_2$-laser pulse tuned to the infrared active ${\nu }_3$ mode. Results are presented over a pressure range from 13 Pa (100 mTorr) to 270 Pa (2 Torr). The pressure dependence clearly proves that the increase does not depend on collisions. The effects are studied as a function of time and of the infrared energy fluence, infrared wavelength, and infrared pulse duration. The experimental data show that an intramolecular equilibrium of vibrational energy is established within the 20-ns time resolution of the experimental setup. The multiphoton excitation shows a red shift and intensity broadening. A comparison with results from photoacoustic measurements is made.

We have studied the odd-parity autoionizing levels in xenon by two-photon laser spectroscopy from the 6s${\left[\mathrm{}\right(3/2\left)\mathrm{}\right]}_2$ metastable level via various J=1,2 6p’ intermediate levels. Observed Rydberg series are ns’${[1/2]}_0$,1, nd’${\left[\mathrm{}\right(3/2\left)\mathrm{}\right]}_1$,2, and nd’${\left[\mathrm{}\right(5/2\left)\mathrm{}\right]}_2$,3 with n ranging to, in some cases, n>80. This is the first observation of J≠1 odd-parity autoionization in xenon. These spectra are notable for the absence of the very intense, broad transitions to nd’${\left[\mathrm{}\right(3/2\left)\mathrm{}\right]}_1$ which dominate photoabsorption from the J=0 ground state. We here present energy-level measurements for 140 levels. These extensive new data should be useful for further multichannel quantum-defect theory analysis of xenon.

The creation of multiple photon-dressed discrete states in the continuum by coupling N levels to a single resonance (atomic or molecular) is discussed. The conditions for the appearance of such states are established along with the experimental consequences that would reveal their presence. These include time-resolved ionization measurements as well as analysis of ionization yield as a function of frequencies.

We use a quantum-electrodynamical, many-body treatment to show mirrorless optical bistability in terms of the spatial properties of coherent dipole-dipole interactions among interacting two-level atoms. The general theory is applied to two special cases: (1) a thin sample of two-level atoms, with a width smaller than a resonance wavelength and (2) a long sample of two-level atoms, with dimensions very large relative to a resonance wavelength. While for the thin sample we are able to use a mean-field approximation with validity, for the long sample we are compelled to take into account retardation and propagation. In both cases bistability is found to be related to a renormalization of the frequency (or relaxation rate) that is inversion dependent. For the long sample the frequency renormalization is significant for high atomic densities and for large oscillator strengths.

The performance of an interferometric gravity-wave detector is analyzed, treating both the motion of the mirrors and the optical fields quantum mechanically, in continuous time. Kerr cells in each arm of the interferometer are used to counter the effects of radiation-pressure fluctuations, a feedback loop is used to keep the interferometer operating at the proper null, and a large mean-field assumption is used to linearize the analysis. When narrow-band disturbances are being measured, the performance of this interferometer can greatly surpass the standard quantum limit. When the Kerr cells are removed, the interferometer operates at the standard quantum limit, and this analysis agrees with earlier studies.

The coupled third-order equations of motion of the two-mode ring laser with spontaneous emission noise are investigated in the presence of detuning and backscattering. The steady-state solution is obtained without linearizing approximations, and it is shown to depend on backscattering only through the sum $R_1$+$R_2^{\mathrm{*}}$, where $R_1$ and $R_2$ are complex backscattering coefficients. Above threshold the effect of backscattering is found to be equivalent to incrementing the pump parameter of each laser mode by (1/2)‖$R_1$+$R_2^{\mathrm{*}}$‖. The variations of the mean light intensities of the two modes with detuning are calculated for several different pump parameters, from well below to well above threshold. The results are compared with direct measurements of a He:Ne ring laser, and good agreement is obtained over a wide range, with the adjustment of just a single scale constant.

We consider the nonlinear three-wave stimulated Brillouin scattering where an initial electromagnetic wave packet grows backward in the expense of a constant input pump wave. For long interaction times we show in particular that the backscattered wave envelope exhibits a set of large peaks of decreasing amplitude, the intensity of the first one growing as $t^2$ while its width shrinks as 1/t. Moreover, the sound-wave amplitude saturates. In the limit case of strong damping of the sound wave the asymptotic behavior is quite different. Implications of these results are considered concerning the observed mechanical fracture of an optical fiber supporting a large laser pulse.

New exact forms for the equation for the resolvent operator are presented which take into account strong-interaction effects. The advantages of the method are illustrated by the exact solution of a problem in which the potential contains a random element.