The secondary-electron yields Y are measured for ${}_{}{}^1{}_{}{}^{}\mathrm{H}_{}^{1+}{}_{}{}^{}$, ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{2+}{}_{}{}^{}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{2+}{}_{}{}^{}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{4+}{}_{}{}^{}$, ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}_{}^{5+}{}_{}{}^{}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{}^{6+}{}_{}{}^{}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}_{}^{8+}{}_{}{}^{}$ ions with 1.5–11 MeV/amu of kinetic energy hitting gold, aluminum oxide, and tantalum targets. For such fast ions, it is expected that the yield will scale as Y∝${\mathit{z}}^2$, where z is the charge state of the ion. The yield data are reduced to remove the kinetic-energy dependence and it is found that Y∝${\mathit{z}}^{1.71}$ for gold targets, Y∝${\mathit{z}}^{1.62}$ for ${\mathrm{Al}}_2$${\mathrm{O}}_3$ targets, and Y∝${\mathit{z}}^{1.72}$ for tantalum targets. Reasons for the deviation of the data from the expected Y∝${\mathit{z}}^2$ scaling law are explored. The electric fields arising from space-charge separations in the wakes of the fast ions are suspected to be the cause of the lowered scaling law.

A fast ion passing through a metal target drives electrons out of its path by means of Coulomb scattering. Some of these electrons escape the target and are denoted as secondary electrons. The rapid displacement of electrons from the ion’s path produces a charge separation in the metal, which gives rise to an electric field in the wake of the ion. For z>1 ions, the wake fields can be so strong that they retard the movement of electrons away from the ion’s path, which reduces the number of secondary electrons that escape the target. The time-dependent electric fields behind fast ions in metals are modeled and the motion of Coulomb-scattered electrons in these fields is examined. The fraction of the electrons that are trapped by the wake is estimated and from this the reduction in the yield of secondary electrons is quantified. The results are in agreement with measurements of secondary-electron emission by fast, high-z ions hitting metal targets.

A dual-laser-plasma technique has been used to measure photoabsorption by atomic Cr and Mn and their ions at photon energies between 40 and 70 eV, where the dominant absorption mechanism is excitation of the 3p subshell. No dramatic differences are observed between the absorption spectra of Mn and ${\mathrm{Mn}}^{+}$, and these spectra are similar to those of Mn metal and ${\mathrm{MnCl}}_2$. The spectra of Cr and ${\mathrm{Cr}}^{+}$ are strikingly dissimilar, the mean excitation energy being about 5 eV greater in the ion. We attribute this to strong mixing of the localized 3${\mathit{d}}^6$ configuration with 3${\mathit{d}}^5$nd Rydberg configurations, an effect that is also responsible for the anomalous appearance of the Cr spectrum with respect to those of the other iron-period elements. The absorption spectra of Cr metal and ${\mathrm{CrCl}}_2$ take forms intermediate between those of Cr and ${\mathrm{Cr}}^{+}$. We give spectroscopic assignments to most of the sharp absorption features of ${\mathrm{Cr}}^{+}$ and determine the 3p ionization thresholds from quantum-defect analysis.

Time-resolved collinear fast-beam laser spectroscopy has been used to measure the lifetime of the T=23 537 ${\mathrm{cm}}^{\mathrm{-}1}$, J=9/2 odd-parity [abbreviated as (23 537)${\mathrm{°}}_{9/2}$] level in Nd ii. Nanosecond pulsed excitation was achieved with the Doppler switching technique. The fast ions were selectively excited from the metastable 4${\mathit{f}}^4$5d ${}_{}{}^6{}_{}{}^{}$${\mathit{K}}_{9/2}$ level to the (23 537)${\mathrm{°}}_{9/2}$ level by the light of a cw dye laser. The decay of the resonance fluorescence photons emitted in the transition to the ground 4${\mathit{f}}^4$6s ${}_{}{}^6{}_{}{}^{}$${\mathit{I}}_{7/2}$ level, as a function of the flight distance, was observed. The decay length was scaled into the decay time by the ion velocity, which was determined using the optical resonance itself. The lifetime is 27.7(9) ns.

The angular distribution and polarization of the L-shell fluorescent x rays excited by 59.57-keV photons in Th and U have been measured. It is found that the Lγ group of L x rays is isotropic in spatial distribution and unpolarized but, the Ll and Lα groups are anisotropically distributed and are polarized. Although no anisotropy of the Lβ group is detected, it is found to be slightly polarized. The present results contradict the predictions of the calculations of Cooper and Zare [Atomic Collision Processes (Gordon and Breach, New York, 1969)] that after photoionization the magnetic substates of all subshell vacancy states are equally populated. However, the present results confirm the predictions of Flügge, Mehlhorn, and Schmidt [Phys. Rev. Lett. 29, 7 (1972)] that the population distribution of the magnetic substates of all subshell vacancy states with j>1/2 is nonstatistical.

We have studied the multielectron dissociative ionization of CO in the range of ${10}^{13}$–${10}^{15}$ W/${\mathrm{cm}}^2$ (laser wavelength 305 and 610 nm; pulse duration 1.4 and 2 ps, respectively). By measuring the fragment kinetic energies and laser-intensity dependences, we have investigated the detailed dynamics of the interaction process. At 610 nm, the formation of ${\mathrm{CO}}^{3+}$ and ${\mathrm{CO}}^{4+}$ occurs as the molecule dissociates. The transitions occur at well-defined internuclear distances that are shown to be independent of the peak laser intensity. At 305 nm, the ionization processes are found to progress in a different way: CO is multiphoton multiply ionized at the equilibrium internuclear distance of the molecule. This vertical excitation yields fragments with charge states and initial energies lower than at 610 nm. The comparison with the previous results obtained on ${\mathrm{N}}_2$ is discussed.

It is shown that the physical mechanisms that give rise to very narrow resonances in nonlinear spectroscopic line shapes and to laser cooling below the so-called Doppler limit are closely related. A general formalism is developed that can be applied to a wide range of problems in nonlinear spectroscopy and laser cooling. To illustrate the formalism, a calculation of the friction force associated with laser cooling is carried out for several cases of current experimental interest.

We find an upper bound for the sensitivity of Fabry-Pérot interferometric length measurements using inefficient photodetectors. This bound applies to all possible quantum-mechanical states of the light entering the interferometer. It applies to standard photodetection, differenced photodetection, and homodyne detection. In the limit of large photon number we identify the optimal detection scheme and input states. They are homodyne detection with a coherent state in one input port, and a nonvacuum quadrature squeezed state in the other. No other quantum states of the input light give better sensitivity, provided that the interferometer output is measured by either photodetection or homodyning, and that the photodetectors are inefficient.

The electron dynamics in the inverse free-electron-laser (FEL) accelerator is investigated by a one-dimensional FEL simulation code. Changing the gradient of the wiggler-field tapering, the electron bunch length in acceleration buckets and the trapping fraction are found to vary. When an infrared laser of 60 GW is focused to a 280-μm-diam laser spot, the maximum acceleration rate reaches 100 MeV/m and the bunch length is about 1/14 of the laser wavelength. In multifrequency analysis, an unstable phenomenon is found that is due to the resonance between the synchrotron motion and beat of a broadband laser radiation. The resonance width for the instability is greater than O(0.1) of the synchrotron frequency when the sideband intensity is higher than a few percent of the carrier wave intensity.

Two-mode instability in a ${\mathrm{CO}}_2$ laser with a saturable absorber is investigated both experimentally and theoretically. A strong correlation is found between the mode competition and the passive Q-switching behavior. The observed two-mode instability is nicely reproduced by our rate-equation model in which the vibrational relaxation processes and the spatial mode coupling are considered. Furthermore, numerical calculation predicts existence of chaos in the two-mode oscillation with a higher fractal dimension than the single-mode chaos.

Analytical expressions for the emission spectrum and intensity correlation functions are derived for a ssV-type three-level atom driven by two strong, resonant coherent fields. It is found that coherent mixing of the atomic states by the strong fields modifies the atomic decay dynamics, which results in dramatical narrowing of spectral features predicted by Narducci, Oppo, and Scully [Opt. Commun. 75, 111 (1990)].

We consider the atomic inversion in the Jaynes-Cummings model when the field mode is detuned from the atomic transition frequency. We find that, unlike in the resonant case, the time average of the inversion depends on the initial state of the atom. This time average is compared to that obtained from a semiclassical model in which the quantized field mode is replaced by a classical driving field. The averages are found to be identical. This similarity disappears when one examines the deviation of the inversion from its mean. The inversion is found to remain much closer to its mean, on average, with a quantum field rather than with a classical one. We also compare the trajectories described by inversions at different detunings. This is done by defining a distance between different trajectories. The distance between the trajectory at zero detuning and that at a detuning of Δ is found to take sudden, discontinuous dips at certain values of Δ.

A system of radiative close-coupling equations for a hydrogen atom in a circularly polarized intense laser field is derived. The radiative scattering matrix is parametrized within a multichannel quantum-defect formalism. The quasienergy spectrum corresponding to nonperturbative shifts and ionization widths of the bound atomic states is computed from the poles of the radiative scattering matrix. For an intensity range up to ${\mathrm{\alpha }}_0$≊1.5${\mathit{a}}_0$ (with ${\mathrm{\alpha }}_0$ the oscillation amplitude of the free electron in the laser and ${\mathit{a}}_0$ the Bohr radius), numerical results are presented in the frequency regime where two-photon ionization and above-threshold ionization of the ground state is possible. For one-photon transitions a stabilization of the atomic states for strong fields is predicted.

The existence of odd Raman subharmonics in the nonlinear mixing of fields of frequencies ${\mathrm{\omega }}_{\mathit{l}}$ and ${\mathrm{\omega }}_{\mathit{s}}$ is examined in a nonperturbative way. It is shown that the coupling of Stokes and anti-Stokes processes at high pump powers produces odd subharmonics in nonlinearly generated signals. It is also shown that this coupling can lead to gain at the odd subharmonics. An effective Hamiltonian is used to discuss the coupling of Stokes–anti-Stokes processes. Numerical results showing the odd subharmonics are presented. The origin of odd subharmonics in terms of transitions among dressed states is also discussed.

Studies of the spectral content and stability of an intracavity second-harmonic ring laser show that single-mode cw operation is stable against amplitude-modulated fluctuations, whereas frequency-modulated fluctuations are undamped. cw operation tends to single longitudinal mode output under very general conditions provided frequency modulation is not introduced. Multimode frequency-modulated cw operation can be achieved. Methods for producing an anti-mode-locked laser and a frequency-modulated laser are described. However, the presence of an intracavity spectral filter will remove frequency modulation. The importance of a spectral filter to restrict the fundamental frequency to the phase-matched bandwidth of the doubler is emphasized.

The free induction decay (FID) and light-echo kinetics are calculated under the assumption that a two-level system frequency is a purely discontinuous noncorrelated Markovian process, and its statistical distribution is a bi-Lorentzian contour. The latter assumption is primarily mathematical, but useful. The model allows one to obtain an exact solution of the FID problem, which recovers the results obtained earlier with perturbation theory (the fast modulation limit) as well as the result concerning the slow modulation limit. It is shown that only in the latter case does the field dependence of the FID rate found by De Voe and Brewer [Phys. Rev. Lett. 50, 1269 (1983)] have a self-consistent explanation.

Theoretical studies of self-induced transparency have used the slowly varying envelope approximation with perturbative corrections. These analyses indicated that for a carrier wave of given frequency, there was a continuum of possible steady-state pulse velocities. We show that the exact steady-state solutions of the full Maxwell-Bloch equations do not share this property; instead, there is a nonperturbative selection mechanism: a carrier wave of given frequency gives rise to steady-state pulses with discrete values of the velocity only. We present analytical and numerical calculations, and suggest some experiments for the semiconductor CdS.

Squeezing transformations in the discrete ${\mathit{Z}}_{2\mathit{j}+1\mathrm{}}$×${\mathit{Z}}_{2\mathit{j}+1\mathrm{}}$ angle–angular-momentum phase space are shown to be associated with the SL(2,${\mathit{Z}}_{2\mathit{j}+1\mathrm{}}$) group and important special cases are explicitly constructed. ‘‘Spherical’’ bases are introduced in the direct sum of all the Hilbert spaces ${\mathit{H}}_{2\mathit{j}+1\mathrm{}}$ and the corresponding representations are defined. Transformations of these bases, using area preserving diffeomorphisms on a sphere, are studied and potential applications in quantum-optics models are discussed.

In this paper a phenomenological semiclassical theory of pulsed-laser-pumped dye-laser light amplifiers is presented. The theory accounts for the broadband radiation absorption and emission characteristics of dye molecules in liquid solvents. Dye-molecule fluorescence, vibrational, rotational, and electric polarization relaxation processes are represented by phenomenological relaxation rates. In general, it is found that due to dye-molecule rotational relaxation the laser-pumped dye medium is optically anisotropic. The pump- and dye-laser beams propagate through the dye medium as essentially transverse electromagnetic waves whose amplitude and polarization state changes. The theory is applicable to pulse durations τ≲10–100 ns including the ultrashort pulse regime. The regime τ≳1 ps in which the pump- and dye-laser pulse lengths are long compared to the dye-molecule vibrational and electric polarization relaxation times is considered in detail. Amplification of partially polarized quasimonochromatic light is described by a self-consistent set of equations for the components of the pump- and dye-laser light coherency matrices and the orientation populations of the lowest vibronic levels of the dye molecule’s ${\mathit{S}}_0$ and ${\mathit{S}}_1$ electronic states.

The interaction of the pump- and dye-laser beams with the dye molecules is characterized by complex electric susceptibility tensors. Kramers-Kronig or Hilbert transform relations are found that permit dye-molecule absorption and emission cross sections to be used to calculate the pump- and dye-laser susceptibility tensors. All the physical parameters in the theory may be determined by conventional experimental techniques. When the dye-molecule rotational relaxation rate ${\gamma }_{\mathit{R}}$ is much larger than the fluorescence rate ${\gamma }_{\mathit{F}}$, ${\mathrm{\tau }}^{\mathrm{-}1}$, and the pump-laser absorption and dye-laser stimulated emission rates, then the dye-molecule electric susceptibility tensors are diagonal. The laser-pumped dye-laser medium is optically isotropic. When these conditions do not hold the medium is optically anisotropic and coherency matrices may be used to describe the propagation of the pump- and dye-laser beams. This procedure is illustrated for the case of transversely pumped dye lasers. In the small-signal regime analytic solutions for the dye-laser-light coherency matrix components are developed for arbitrary initial polarization state, pulse duration, and ${\gamma }_{\mathit{F}}$/${\gamma }_{\mathit{R}}$. In the large-signal regime numerical solutions are obtained for the amplification of short, (τ${\gamma }_{\mathit{F}}$,τ${\gamma }_{\mathit{R}}$)≪1, and quasi-steady-state (τ${\gamma }_{\mathit{F}}$,τ${\gamma }_{\mathit{R}}$)≫1, pulses for arbitrary values of ${\gamma }_{\mathit{F}}$/${\gamma }_{\mathit{R}}$ when the pump- and dye-laser polarizations are parallel. In general, it is found that for a wide range of physical conditions of interest dye-molecule rotational relaxation is important, and significant changes in the amplification characteristics of the medium, i.e., the rate of amplification, amplification efficiency, and polarization state of the light, will occur.

The unitary operator for transforming individual particles’ coordinates to Jacobi coordinates is constructed in terms of a simple mapping of the classical transformation to quantum Hilbert space in Dirac’s coordinate representation. The corresponding normally ordered form of the unitary operator is easily obtained by integration within ordered products.