We show that regularization of pumping leads to large photon-number noise reduction in one- and two-photon micromasers, and is much more important than in macroscopic lasers and masers. Our calculations are based on a step-by-step microscopic approach and are compared to results obtained from a pumping-statistics-dependent master equation, which is shown not to be entirely reliable in the micromaser case. Although noise reduction and the discrepancies betwen the two approaches are more important for monokinetic beams, they are still relevant when a 10% velocity dispersion is allowed.

Two different mechanisms of annihilation of discrete quasienergy states in strong electromagnetic fields are described. In the first mechanism, the annihilation of a metastable Floquet state results from laser-induced avoided crossing between two quasienergy levels. The second mechanism is basically a threshold effect where the ionization or dissociation energy of a specific bound state of the field-free Hamiltonian (bound state of the diagonal term in the Floquet Hamiltonian matrix in the general case) is equal to nħω, where ω is the frequency of the time-dependent field and n is the number of absorbed photons. An illustrating numerical example is given.

The natural linewidth of a one-photon micromaser for a certain choice of interaction time has been calculated using the exact solution of a second-order correlation function. A comparison is made with the corresponding linewidth of a laser.

We calculate the amplitude squeezing in the output of a coherently pumped four-level laser and compare it with that from a similar incoherently pumped laser. We find that squeezing may be considerably enhanced by pumping with coherent light. The squeezing in both types of laser is explained by a simple statistical model.

We consider the reduction of the intensity fluctuations in a laser by intracavity nonlinear absorption. The optimum operating conditions for reducing the intracavity intensity fluctuations are not the same as the conditions for reducing the intensity fluctuations in the output field. For a quite general class of models, we show that at the optimum operating point for reducing intensity fluctuations in the output field reduction in the intracavity intensity fluctuations is half of the maximum level that can be achieved in the model. We also show that as the laser intensity fluctuations are reduced the phase fluctuations, as measured by the laser linewidth, are correspondingly increased.

We report the measurement of excited-state lifetimes in highly ionized silicon atoms using multiplexed detection of a fast-ion beam source. Simultaneous lifetime measurements for resonance transitions and for Rydberg transitions in Si xi and Si xii have been performed. Comparisons with theoretical lifetimes are presented, and good agreement is obtained with a new relativistic many-body calculation of the 2p fine-structure-state lifetimes in lithium-like Si xii.

A recently developed approach for the direct calculation of electron density is implemented for polyatomic molecules: benzene and a tetrapeptide with four glycine residues. The method uses the density as the basic variable, divides a system into subsystems, and determines the density for each subsystem. It is found that the method is capable of describing the electronic structure with accuracy comparable to the Kohn-Sham method. This substantiates the hope for ab initio calculations of large systems beyond the reach of conventional methods.

A many-electron, many-photon theory has been applied to the computation of static α and dynamic α(ω) linear polarizability of the ${\mathrm{H}}^{\mathrm{-}}$ 2${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$P state. The calculation involves the nonperturbative mixing of one bound (2${\mathit{p}}^2$ ${}_{}{}^3{}_{}{}^{}$P), and one autoionizing (2s2p ${}_{}{}^3{}_{}{}^{}$P° ) state with 13 continua. State-specific, compact, and accurate square-integrable wave functions have been employed. The magnitude of the polarizability is huge: α=64 000 a.u.

A coupled-channel optical method for electron-atom scattering is applied to elastic electron-sodium scattering at energies of 20, 22.1, 54.4, 100, and 150 eV. It is demonstrated that the effect of all of the inelastic channels on elastic scattering may be well reproduced by the ab initio calculated complex nonlocal polarization potential. The results are found to be in good agreement with the recent experiments of Lorentz and Miller (unpublished).

The Glauber approximation is used to calculate doubly differential cross sections (DDCS’s) for electron-impact ionization of helium at incident energies of 100, 300, and 500 eV. Angular dependences of the cross sections are presented for the primary (scattered) electrons. The present calculation is done for the case where the energy of the primary electron is large compared with that of the secondary (ejected) electron. A comparison is made of the present DDCS with the results of other calculations and experiment.

High-resolution photoabsorption spectra of ${\mathrm{SF}}_6$ and ${\mathrm{PF}}_5$ at the ${\mathit{L}}_{2,3}$ edge in the gas and solid phase have been measured with synchrotron radiation. A reduction in the intensity for some of the higher-energy transitions in the condensed phase indicates significant Rydberg character associated with the terminating orbitals. This observation is consistent with the assignments suggested by multiple-scattering Xα calculations and suggests that Rydberg orbitals can penetrate into the potential barrier created by the electronegative atoms.

We report a numerical study of the parametric sensitivity of quantum kicked tops in the classically chaotic regime where their quasienergy spectrum is irregular. We calculate the statistical distribution of the level curvatures defined as the second derivative of the eigenphases of the Floquet operator with respect to the parameter. We show that the curvature density for the orthogonal, unitary, and symplectic systems decreases, respectively, as ‖K${\mathrm{\Vert }}^{\mathrm{-}3}$, ‖K${\mathrm{\Vert }}^{\mathrm{-}4}$, and ‖K${\mathrm{\Vert }}^{\mathrm{-}6}$ for large curvatures ‖K‖, in agreement with theory.

We present evidence obtained from numerical experiments that strong-field stabilization of atoms can occur in the context of photon frequencies as low as those corresponding to three-photon ionization of the ground state of a quasihydrogenic atom.

We comment on statements made about quantum representation theory in the paper by T. W. Marshall and E. Santos [Phys. Rev. A 41, 1582 (1990)]. Results are presented which show that correct results can be obtained from Langevin equations derived from the positive-P representation, even when those obtained by truncation of the Wigner time-evolution equation give incorrect results.

We try to place the preceding Comment by Kinsler and Drummond [Phys. Rev. A 44, 7848 (1991)] in an overall scientific context.

We show, in addition to giving some clarification about the rescaling problem, that the symmetry transformations preserving the radial form of the Schrödinger equation discussed recently by Janke and Kleinert [Phys. Rev. A 42, 2792 (1990)] are also able to produce a further Hamiltonian form.