Absolute cross sections have been measured from below threshold to 1500 eV for electron-impact single ionization of chromium ions in initial charge states 6+, 7+, 8+, and 10+. The measurements utilized the Oak Ridge National Laboratory Electron Cyclotron Resonance ion source and electron-ion crossed-beams apparatus. The lowest three charge states, which have 3$s^2$3$p^n$ ground-state electron configurations, all exhibit ionization onsets at lower energies than expected for ground-state ions, indicating the presence of ions in metastable configurations in the incident beams. Significant contributions to the total cross sections by excitation autoionization are observed for each ion. The present measurements are compared to calculations of direct ionization from the Lotz formula, and the ${\mathrm{Cr}}^{10+}$ measurements are compared to previous data for the isoelectronic ion ${\mathrm{Ni}}^{14+}$.

Closing the series on the use of the norm method as a practical criterion to determine translation factors, we report a considerable simplification of the computational effort involved in our method. We study the speed of convergence of the sum-over-states expression giving the norms, and the possible use as criteria of rough approximations obtained by truncating this sum to a few states. Our main conclusion is that the rough-approximation method would yield the same translation factors as the exact one, while involving a minimal additional programming effort to that of the evaluation of molecular energies and couplings, and being applicable to semianalytical as well as variational wave functions, state-dependent as well as common translation factors, and package as well as ad hoc molecular programs.

Theoretical predictions are presented for the iron Kα x-ray emission spectra from high-temperature plasmas, assuming steady-state optically thin excitation conditions. Account has been taken of all fine-structure components of the 2p→1s inner-shell-electron radiative transitions in the iron ions from Fe xviii to Fe xxiv. The Kα emission spectra are assumed to be produced by means of dielectronic recombination and inner-shell-electron collisional excitation processes that involve intermediate autoionizing states belonging to electronic configurations of the type 1$s^1$2$s^r$2$p^s$. In addition to the electron-temperature variation, which is attributable to the temperature dependences of the radiationless electron capture and inner-shell-electron collisional excitation rate coefficients and to the temperature dependence of the charge-state distribution, the Kα emission spectra exhibit an electron-density sensitivity. This electron-density sensitivity is a result of the density-dependent distribution of populations among the different fine-structure levels of the initial ions in the dielec- tronic recombination and inner-shell electron collisional excitation processes.

In order to introduce a simplified treatment for the initial distribution of populations, whose precise determination would involve the detailed and self-consistent description of a multitude of elementary atomic autoionization, collision, and radiation processes, the electron-density range of interest has been subdivided into three, increasingly dense, regions. In the low-density region, which is expected to be appropriate for astrophysical plasmas such as solar flares and supernova remnants, it has been assumed that only the lowest-lying fine-structure levels of the ground-state electronic configurations of the initial ions are populated. Magnetically confined laboratory plasmas, such as tokamaks, are represented by the intermediate-density region, in which the initial ion populations have been assumed to be statistically distributed among all fine-structure levels of the ground-state electronic configurations. In the high-density region, which is expected to occur in laser-produced and vacuum-spark-produced plasmas, the populations of the initial ions have been assumed to be statistically distributed among all fine-structure levels of not only the ground-state electronic configurations but also the additional configurations which can be derived from the ground-state configurations by means of 2s→2p excitations. The inclusion of these additional excited configurations of the initial ions not only alters the intensities of the satellite lines that are predominant at low densities, but it also introduces additional satellite lines that occur at different wavelengths. Discussions are presented on the consequences of this electron-density sensitivity of the Kα satellite emission for the spectroscopic determinations of electron temperatures, electron densities, and charge-state distributions in both astrophysical and laboratory plasmas.

The x-ray-absorption cross section in atoms both without and under intense laser fields is recalculated on the basis of gauge-invariance requirements in the first-order Born approximation. Better approximations of the intense-field-assisted x-ray-absorption cross section are also proposed.

For the computation of the induced dipole moments, the collisional ${\mathrm{H}}_2$-${\mathrm{H}}_2$ complex is treated as a molecule in the self-consistent field and size-consistent, coupled electron pair approximations. The basis set accounts for 95% of the correlation energies and separates correctly at distant range. The average of the induced dipole components is obtained for the case of both ${\mathrm{H}}_2$ molecules in the vibrational groundstate (v=v’=0) and recast in a simple but accurate analytical form. The analytical dipole expression is used for computations of the spectral moments (sum rules) and line shapes of the collision-induced rototranslational absorption spectra of molecular hydrogen in the far infrared, over a range of frequencies from 0 to 2200 ${\mathrm{cm}}^{\mathrm{-}1}$, and for temperatures from 77 to 300 K, using a quantum formalism. Proven isotropic potential models are input. Numerical consistency of the line-shape calculations with the sum rules is observed at the 1% level. The comparison of the computational results with the available measurements shows agreement within the estimated uncertainties of the measurements of typically better than 10%. This fact suggests that the theory is capable of predicting these spectra reliably at temperatures for which no measurements exist.

An exact solution for the dressing of a bound-state wave function by a plane-wave electromagnetic field is written in terms of the set of bare states. The solution is stated in the radiation gauge as an infinite series involving powers of the field frequency. The leading term of this series gives a simple analytical form for a state dressed by the field when the energy of a single field photon is much less than transition energies in the bound system. The result is closely related to the momentum-translation approximation (MTA) wave function. The MTA result is thereby shown to follow in a fixed gauge from an exact solution of the fully interacting Schrödinger equation.

The multiconfiguration Hartree-Fock method, which has been extended to study photoionization of atoms, is applied to calculate the 3s→kp photoionization cross section of argon. It has been shown that the interchannel interaction associated with the 3p→kd transition, which is very strong in the 3s subshell photoionization cross section, can be very efficiently simulated by the bound-continuum channel interaction associated with the 3p→3d transition. The length and velocity forms of cross section agree very well throughout the range of energies considered. Our results compare well with other theoretical estimates and are in better agreement with experimental measurements.

The atomic transition probabilities and radiative lifetimes of neutral argon have been the subject of numerous experiments and calculations, but the results exhibit many discrepancies and inconsistencies. We present a unified set of atomic transition probabilities, which is consistent with essentially all recent results, albeit sometimes only after critical reanalysis. The data consistency and scale confirmation has been achieved in two ways. (i) We have carried out some lifetime–branching-ratio measurements for a principal 5p level and the associated 4s-5p transitions. These measurements have very closely confirmed the accuracy of the results of recent independent emission experiments. (ii) We have critically reanalyzed and revised the literature data for the 4s-4p transitions, as well as utilized the results of a similar critical analysis for the 4s-5p transition array, to establish complete sets of absolute data for these arrays. We have found these data to be mutually consistent from cross-correlation checks between the two arrays, using recent literature data. Finally, we have proposed renormalization factors for other argon transitions based on this analysis.

The Stark effect of the sodium $D_2$ line was investigated by use of high-resolution laser-atomic-beam spectroscopy. The shift and splitting of the hyperfine components of the line could be obtained and compared with theoretical calculations. This allows the determination of the scalar and tensor polarizabilities with high accuracy to be 49.28(15) and -21.97(10) kHz/(kV/cm${)}^2$, respectively. These values are compared with semiempirical calculated polarizabilities. Additionally, the behavior of the relative intensity of the components could be studied. In fields greater than 100 kV/cm, the two groups of components with $M_J$=(1/2 and (3/2 are widely separated and the pattern of each group is independent from the field strength, showing an ‘‘electrical’’ Paschen-Back effect. The relative intensities agree satisfactorily with the computations.

A full theory of the interaction between nonlinear transverse-electric and transverse-magnetic waves is derived. A new form of third-order tensor that accounts for the presence of the two polarizations is described and a mathematical discussion of the first integral is presented. The theory is illustrated by a full set of numerical results both for single-interface and thin-film structures.

In nondegenerate parametric amplification of light, one pump photon is destroyed and two photons are simultaneously created, one in each of two modes with different frequencies (the signal and idler). If m signal photons are counted in time t, what is the state of the idler conditioned on this result? The projection postulate cannot be used to answer this question as photon-counting measurements are not ‘‘first-kind’’ measurements. We use a theory of continual quantum-counting measurements to show that in general the idler field is left in a classical mixture of number states with at least m quanta. In an appropriate limit this mixture reduces to an exact number state with m quanta.

We consider a system of two lasers. The output of each laser is injected in the other laser after a possible attenuation of the field intensity. We formulate the laser equations in the good-cavity limit and show that there is a coupling between intensities and phases. If the coupling is small, the long-time response of each laser is time periodic and is similar to the response of a laser with periodic loss modulations. Resonance effects are possible and may lead to interesting bifurcation diagrams when the free lasers are different. We investigate the weak-coupling limit for arbitrary values of the pump parameters. The resonance problem is analyzed for values of the pump parameters close to the laser first threshold. If the coupling is moderate, stable steady-state solutions are possible. The transition from time-periodic to steady-state responses appears at a critical coupling amplitude. We propose an asymptotic analysis of the laser equations which is valid for values of the pump parameters close to the laser first threshold.

The response of a phase-conjugate mirror (PCM) based on nondegenerate four-wave mixing to an incident photon wave packet has been calculated. In the monochromatic limit the phase-compensating property of the PCM, which makes the response independent of optical path length, is recovered. However, for a photon wave packet of nonzero bandwidth, the response of the PCM varies in a fairly complicated manner with the wave-packet length. In particular, the length of the pulse reflected from the PCM becomes independent of the length of the incident pulse for sufficiently short pulses.

Based on an analytical criterion function, we have carried out a detailed investigation of the global structure of the unstable regions of the single-mode optical bistability system in parameter space.

We present the results of an experimental effort to generate squeezed microwave radiation using the phase-sensitive gain of a Josephson parametric amplifier. To facilitate the interpretation of the experimental results, we first present a discussion of the theory of microwave squeezing via Josephson parametric amplifiers. This is followed by a detailed description of the device fabricated for our experiment. Experimental results are then presented for the device used in both the doubly degenerate or four-photon mode and for the degenerate or three-photon mode. We have observed parametric deamplification of signals by more than 8 dB. We have demonstrated squeezing of 4.2-K thermal noise. When operated at 0.1 K, the amplifier exhibits an excess noise of 0.28 K when referred to the input. This is smaller than the vacuum fluctuation noise level ħω/2k=0.47 K. The amplifier is thus quieter than a linear phase-insensitive amplifier in principle can be.

This paper investigates the stabilizing influence of axial momentum spread on the linear growth properties of the cyclotron autoresonance maser (CARM) instability. The stability analysis is based on the linearized Vlasov-Maxwell equations for a relativistic electron beam and right-circularly-polarized electromagnetic waves propagating parallel to a uniform magnetic field $B_0$e${^}_z$. Detailed stability properties are investigated for a choice of beam equilibrium $f_b^0$($p_{\perp }^2$,$p_z$) that incorporates both an inverted population in perpendicular momentum $p_{\perp }$ and a spread Δ in axial momentum $p_z$. For simplicity, the analysis neglects the influence of finite radial geometry ($k_{\perp }$→0 and no radial waveguide structure). The resulting dispersion relation is analyzed numerically in parameter regimes of interest for CARM applications, and approximate analytical estimates of the (reduced) growth rate are presented.

In super-regenerative detection, a weak external signal is amplified in an oscillator that is periodically switched on and then quenched. It is shown that very weak optical signals, slightly above the noise level, can be detected effectively by a laser used as a super-regenerative receiver. The detector output for different signal levels and its operating characteristics are determined by numerical integration of stochastic differential equations that represent the growth of laser radiation from a background consisting of signal and noise.

The second-order susceptibility is calculated in a time-dependent, fully quantized system using coherent states. This is done for the two different interaction Hamiltonians of quantum optics, and the results are compared and discussed. Also, the contribution from the second harmonic originally present in the incident beam is separated out and its effect is assessed.

Temporally and spectrally resolved large-angle Thomson scattering was used to study the frequency and damping of short-wavelength (k${\lambda }_{\mathrm{De}}$∼1) ion acoustic fluctuations in a plasma in the presence of a high-frequency (${\omega }_0$>${\omega }_{\mathrm{pe}}$) laser beam. At high laser intensities ($v_{\mathrm{osc}/v_e>1\mathrm{}}$), the frequency of the ion acoustic waves which propagated parallel to the electric field of the laser (i.e., parallel to the electron quiver velocity) was observed to be larger than the frequency of the waves which propagated in the perpendicular direction. An increase in the fluctuation amplitude for those waves that propagated parallel to the electric field was observed to be coincident with the shift in the ion acoustic frequency. Both the frequency shift and the increase in the fluctuation amplitude can be explained in terms of the off-resonance ion acoustic decay and the off-resonance oscillating two-stream instabilities. The experimental results are in good agreement with the predictions of theory.

Wave-breaking conditions, in terms of the electron velocity or the maximum wave amplitude, of space-charge waves in a relativistic electron beam are obtained. The discussion includes both negative-energy and positive-energy modes as well as wave propagation parallel and antiparallel to the electron beam.