The Stark shift and splitting of the resonance lines of the lithium atom were investigated in electric fields up to 420 kV/cm, using laser–atomic-beam spectroscopy. The scalar and tensor polarizabilities of the levels 2 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ and 2 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ of both isotopes ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ were accurately determined. The experimentally obtained level polarizabilities are compared with theoretically calculated values.

We describe a numerical implementation of our semiclassical laser-cooling theory [J. Javanainen, Phys. Rev. A 44, 5857 (1991)] for an arbitrary multilevel atom and light field. There is satisfactory agreement between experiments and temperatures obtained from Langevin-equation simulations of the motion of an atom subject to light-pressure force and the accompanying diffusion in three-dimensional (3D) optical molasses in which there are three orthogonal pairs of counterpropagating waves with a common linear polarization for the two beams in a pair, but orthogonal polarizations between the pairs. However, the velocity distribution of the atoms is anisotropic and may deviate strongly from a Gaussian, heterodyne spectra may have a sideband, and the atomic density may be a maximum at the maximum of the potential of the dipole forces of the molasses beams. Subsequent velocity-linearized analysis of atomic damping and diffusion shows that the damping tensor may have a negative eigenvalue corresponding to heating in large regions of space, even though the light is red tuned for cooling. It is also found that the position-averaged damping and diffusion tensors make a poor predictor of the temperature obtained in Langevin-equation simulations and real experiments. Based on additional simulations of a simple 1D model, we formulate a hypothesis that connects our findings. The key idea is that an atom trapped in a minimum of the potential of the dipole forces is subject to a weaker-than-average damping, and therefore tends to boil out of the trap.

We have measured certain ratios of transition intensities between excited hydrogen Stark sublevels over a range of electric-field values. ${\mathrm{CO}}_2$ lasers were used to excite a fast beam of hydrogen atoms. The π-polarized transitions studied were from extremal Stark sublevels of principal quantum number n=10 to extremal and next extremal sublevels of n=30 and 44, at fields from 2 to 700 V/cm. The observed ratios are compared with those obtained using a non-relativistic zero-field formula attributed to Gordon [Ann. Phys. (Leipzig 2, 1031 (1929)] and with calculations employing matrix diagonalization including fine structure. Even for those relatively high n values, we find at low field significant deviations from results from Gordon’s formula due to fine structure in the lower state as well as deviations at high field due to n mixing in the upper state induced by the static electric field. The experimental results and the matrix diagonalization calculations agree to within a few percent, which is the order of magnitude of possible saturation effects.

A rigorous time-dependent wave-operator method within the Bloch formalism is presented and applied to the calculation of the photodissociation rate of ${\mathrm{H}}_2^{+}$ in intense pulsed laser fields. The wave packet is simultaneously propagated on the radiatively coupled ground and electronically excited potential-energy surfaces of the ion, combining a Lanczos reduction technique at low orders and recursive time-dependent Bloch operators. Dissociation rates are extracted from an asymptotic-flow analysis in the momentum space. The energy distributions of the protons, resulting from multiphoton absorption above the dissociation threshold, consist of a sequence of peaks spaced by half of the photon energy. The distribution of higher-energy peaks decreases with increasing intensity, due to stimulated emission from dissociating fragments. Time-resolved dynamics reached by ultrashort intense pulses (≃20-fs duration and peak intensity varying in the range from 3.5×${10}^{12}$ to 3.5×${10}^{14}$ W/${\mathrm{cm}}^2$) leads to a thorough interpretation of photon-exchange mechanisms between the field and the ion during the excitation and fragmentation steps.

Light transmitted through a resonant atomic system with electromagnetically induced transparency displays reduced phase-noise fluctuations. For the case of the medium being inside a cavity, a 50% squeezing of the out-of-phase component is possible outside the cavity.

We provide a model for a two-photon system that possesses quantum-group symmetry. The quadrature-phase amplitudes of the model are defined in terms of deformed oscillator operators. We emphasize the investigation of the most general minimum-uncertainty states, i.e., coherent states and squeezed states, for the quadrature-phase amplitudes ${\mathrm{\alpha }}_1$ and ${\mathrm{\alpha }}_2$. We show that the squeezed states of the two-photon quantum optics are simultaneous eigenvectors of the operators ${\mathit{A}}_{+}$ and ${\mathit{A}}_{\mathrm{-}}$ with eigenvalues ${\mathit{a}}_{+}$ and ${\mathit{a}}_{\mathrm{-}}$, respectively. For an important subset of the squeezed states, the expectation values and variances of relevant operators are given explicitly.

We generalize the electromagnetic mode to be dependent on the deformation parameter and investigate the dynamics of the generalized photonic fields that possess quantum group symmetry interacting with atoms. Radiative decays and line shifts of an excited atom are obtained in this system. When an atom is in an intense field, the time development operator, intensity operator, and the time variation of the photon distribution are given in an explict way both with and without intensity-dependent coupling. The results of Chaichian, Ellinas, and Kulish [Phys. Rev. Lett. 65, 980 (1990)] are recovered in case of resonance. We also discuss the dynamics of the coupled N-atom system in detail.

We investigate two-peak passage-time statistical distributions in a Q-switched ${\mathrm{CO}}_2$ laser using the excitation current as the control parameter. This two-peak statistics is due to the population-inversion noise when the initial laser state is set close to threshold. Such a phenomenon has been experimentally observed in a class-B laser when the passage time is shorter than the relaxation time of the population inversion. The time separation of the two peaks can be quantitatively related to the laser net gain.

We consider the dependence of the four-wave-mixing signal from an ensemble of homogeneously broadened, two-level atoms on the statistics of the pump field. Two models for the pump field are considered: the chaotic field and the phase-diffusing field. A Monte Carlo simulation procedure is used to integrate the equations describing the four-wave-mixing process numerically. This technique allows consideration of arbitrary bandwidths for the pump and incorporates pump-induced saturation effects. Results are presented for the strength of the four-wave-mixing signal as a function of the pump intensity for both resonant and off-resonant cases. It is shown that the four-wave-mixing signal is sensitive to the statistics of the pump, particularly for strong fields.

Recent papers [A. Bechler, Phys. Lett. A 130, 481 (1988); M. S. Abdalla, Phys. Rev. A 44, 2040 (1991)] investigate the generation of squeezing for a charged oscillator in a constant and uniform magnetic field. Here we pursue further this line by investigating the extended system of a charged particle oscillating in a uniform and arbitrary time-dependent magnetic field. Since we do not particularize the functional time dependence, our expressions for the variances of quadratures are quite general, so the possible occurrence and amount of squeezing will depend on that specification. The corresponding results mentioned above become a particularization of ours.

This paper considers the effect of phase-conjugate feedback (PCF) on the noise characteristics of semiconductor lasers. By using the single-mode, rate-equation formalism, it is shown that semiconductor lasers can achieve a steady state as long as the amount of PCF is below a critical value. For an ideal phase-conjugate mirror, the average value of the steady-state phase of the semiconductor laser is found to be locked to a fixed value, determined by the linewidth-enhancement factor of the laser. The noise characteristics in the presence of PCF are studied by adding the Langevin-noise terms representing the effect of spontaneous emission to the rate equations and solving them approximately. Both the intensity noise and the frequency noise are reduced at low frequencies (below 100 MHz). In particular, the frequency noise nearly vanishes at zero frequency because of the phase-locked nature of the steady-state solution. The spectral line shape does not remain Lorentzian in the presence of PCF. The satellite peaks occurring at the relaxation-oscillation frequency are considerably enhanced because of a reduction in the damping rate of such oscillations.

Multipulse photon echoes are observed from ${\mathrm{LaF}}_3$:${\mathrm{Pr}}^{3+}$ and are shown to be primarily stimulated echoes. The various contributions to the echoes were measured using a three-pulse photon-echo sequence that resolved the image of the echo generated by the first two pulses, and the echo generated by the second and third pulses and that of the first and third pulses from the stimulated echo. By use of a theoretical model of Shoemaker [in Laser and Coherence Spectroscopy, edited by J. I. Steinfeld (Plenum, New York, 1978)] and relaxation theory of Hu and Hartmann [Phys. Rev. B 9, 1 (1974)], the image echo contributions to the third echo is shown to be less than 10% of the total for the pulse widths and Rabi frequencies used in the measurements. As a result, multipulse photon echoes will find limited use in measuring coherence decay until very short high-intensity pulses are used to excite the echoes.

A generalized Jaynes-Cummings model when an ideal cavity is filled with a Kerr-like medium is considered. The fluorescence spectrum produced by such a system using the infinity of transitions among the dressed states of the Jaynes-Cummings model is analyzed. A large number of resonances in the spectra are observed that are sensitive to the initial field statistics as well as the nonlinearity of the medium. Also, the fine structure of the spectra gets considerably modified by increasing the nonlinearity of the Kerr-like medium.

A general theory of the micromaser is described. The model is based on treating the input atomic beam as a two-component quantum field so that the two-level atoms in the beam are ‘‘quanta’’ of this field. This approach makes it possible to formulate a general quantum Langevin description of the dynamics with the input atomic field as a source of quantum noise. The passage to a master-equation description is then effected by use of an adjoint-operator method, and by introducing a general class of statistical states for the atomic beam known as generalized shot noise. The result is a (non-Markovian) master equation for the field inside the cavity which is valid for a broad range of statistical properties of the input atomic beam. The approximate steady-state solutions to this master equation for the photon statistics of the cavity field for sub-Poissonian (antibunched) atomic beams found by other researchers are regained. The theory is then extended to treat super-Poissonian (bunched) atomic beams. An exact result is found in the limit of a strongly bunched beam in which the cavity-field state is shown to converge to a mixture of a thermal-field state and the state produced by a random beam of twice the intensity. A physical explanation of this result is also presented.

An alternative momentum-space representation (‘‘impulse representation’’) well adapted to the evaluation of converged nonperturbative solutions of the nonrelativistic time-dependent Schrödinger equation for atoms subject to intense, ultrashort laser pulses is described. Exact expressions for survival, excitation, and ionization probabilities and photoelectron energy spectra are presented for the case of a hydrogen atom struck by a δ-function pulse. A method for the extension of such calculations to realistic ultrashort pulses is described, based on a Sturmian basis expansion of the time-dependent Schrödinger wave function.

We investigated the intensity correlation of a multimode Ar-ion laser. By the measurement of mode spectra and correlation times 20–30 simultaneously lasing modes, it was found that the behaviors of mode fluctuations are largely different between modes away from the center of a lasing line and modes near the center. These characteristics can be explained by the fluctuations caused by mode-mode coupling. Using third-order laser theory, we derived numerically the characteristics observed. We discuss the fitting curves of the correlation functions and the limit of the classical treatment.

One-atom lasers are important because their governing equations can be solved exactly, even with a quantized field. We present a fully quantum-mechanical treatment of one-atom lasers modeled by quantum-optical master equations. These are solved numerically without any significant approximations. We show that laser action is possible with one atom, and that it might be achievable experimentally. Laser action is characterized by the dominance of stimulated emission over spontaneous emission. We use the one-atom laser model to investigate, without approximation, some interesting generic laser phenomena. Under certain conditions lasers produce intensity squeezed light, and then the laser linewidth increases with the pumping rate, in contrast with standard lasers. We also report ‘‘self-quenching’’ behavior: lasers with incoherent pumping out of the lower laser level turn off when the pumping is sufficiently fast because the coherence between the laser levels is destroyed.

Using a cavity with a large Fresnel number, a nontrivial large-scale order resulting from global multimode-interaction dynamics is found in the transverse structure of a ${\mathrm{CO}}_2$ laser beam. Two-dimensional optical lattices displaying several hundred phase singularities each have been observed. The symmetry properties of these far-field patterns and their associate temporal spectra are studied as a function of two control parameters: the Fresnel number and the transverse intermode spacing.

In this paper, we report the theoretical treatment of ultrafast time-resolved hole burning. The description is valid for nonoverlapping and overlapping pulses as well. Also the effects of the temperature are included in the theory. The influence of the various contributions to the transient hole-burning spectrum corresponding to the level population, pump polarization coupling, and perturbed free-induction-decay terms is stressed.

We present collisional-radiative-equilibrium (CRE) gain calculations for the important J=2-1 and J=0-1 3p-3s transitions of neonlike selenium using an extensive set of accurate excited-state couplings and self-consistently calculated ionization and excited-state abundances. An atomic model was put together containing all the most significant processes impacting the gain calculation of these transitions in order to determine the sensitivity of the gain ratio of the J=0-1 to the J=2-1 lines to the monopole excitation cross sections in CRE. It is seen that variations of a factor of 2 or 3 of these cross sections are all that are needed to reverse the calculated J=0-1 to J=0-2 gain ratios. For example, a decrease in the direct excitation rate from the ground to the (1/2,1/2${)}_0$, 3p level by a factor of 3 is sufficient to reverse the gain ratio for the J=0-1 line at 182 Å to the J=2-1 line at 210 Å and move it into agreement with the experimentally observed ratio for these transitions. Experimental observations would suggest that for low-Z elements (Cu, Zn) this ratio is larger than 1, while for high-Z elements (Mo, Sr) it is less than 1. At issue is where the crossover occurs. We draw attention to another instance where the discrepancy between theoretically calculated behavior and experimental behavior can be attributed to the large size of the calculated monopole excitation rate. We also present the calculated temperature and density behavior of the J=0-1 and J=2-1 gains and discuss how this behavior might be used to determine the adequacy of present atomic models to explain experimental neonlike x-ray-laser observations.