We investigate the effect of the dipole-dipole interaction on the dynamic properties and the atomic coherent trapping of a two-identical-atom system in the presence of a laser field by means of quantum-electrodynamics theory. The influence of the dipole-dipole interaction on the collapses and revivals of the atomic population is revealed. The conditions of the atomic coherent trapping are given. A way to measure optically the coupling strength between the atoms is pointed out. We also show that the effect of the dipole-dipole interaction may be screened due to the coherent field in certain atomic superposition states.

We present an experimental study of laser-induced continuum structure in cesium, performed by observing the birefringence and dichroism induced in the atomic medium by a circularly polarized laser embedding the 8s ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$ state into the ionization continuum. The optimization of the sensitivity for the detection of the polarization rotation has allowed a high-accuracy measurement of the resonance profile. A quantitative comparison with theoretical predictions, taking into account the hyperfine structure of atomic levels, shows a clear evidence of a line-broadening effect due to cesium resonant collisions.

The statistics of the difference events in a balanced homodyne-detection scheme is studied without using the standard assumption of a strong, classical local oscillator. Starting from the quantum theory of photon counting, we derive the probability distribution for the difference events in the two detection channels. In the limit of the local oscillator being strong compared with the signal, the difference-number statistics tends to the statistics of the electric-field strength of the signal field. For weak signals, this limit may be obtained already far from a classical behavior of the local oscillator. While changing the local oscillator intensity, a transition of the observable concerning the signal field occurs from the photon-number difference towards the electric-field strength. Such a measurement scheme renders it possible to observe the quantum features of a coherent state or a single-photon state from the point of view of the field-strength statistics, a picture which is closely related to classical optics. The possibility to get some insight in the statistical properties of the phase difference of two microscopic fields is discussed.

We discuss a procedure for the calculation of operator correlation functions that arise frequently in quantum-optics problems. The starting point of our method is the tradiational quantum regression theorem, and its implementation requires only the solution of the master equation for the density operator of the system of interest. An attractive feature of this scheme of calculation is that it offers some distinctive advantages over the conventional Langevin-equations approach or other procedures that rely on the mapping of the density operator into appropriate phase-space distribution functions. Although the practical implementation of this method is likely to require numerical computations for virtually every model of physical interest, the procedure is sufficiently general to allow consideration of both field and atomic correlation functions, as well as multitime expectation values of mixed products of atomic and field operators. In this paper we provide a fairly detailed derivation of the formulas of interest, and illustrate our results with specific examples and tests of the procedure.

We study a cavity QED model where a single three-level atom interacts with four quantized cavity fields in a Raman-type interaction, forming two transition channels for the atom. We show that this system is equivalent to the coupling of three angular momenta, and give its exact eigenenergies and eigenvectors in terms of Clebsch-Gordan coefficients, even if the ac Stark shift is included. Some Heisenberg operators are solved exactly as well as approximately. Dynamical evolution of average photon numbers and the atomic inversion are discussed for several initial conditions and a simple example of model interference is examined.

We investigate the phenomenon of quantum revivals in the Jaynes-Cummings model for an arbitrary quantized field mode. With the help of the Poisson summation formula, we cast the infinite sum determining the atomic inversion into an infinite sum of integrals. Each integral, when evaluated using the method of stationary phase, yields under appropriate conditions one revival. We present simple approximate analytical expressions for these revivals and illustrate this general technique by the examples of a coherent and a highly squeezed state. The oscillatory photon distribution of the latter creates slightly different Rabi frequencies which give rise to a beat note; that is, echos in the revivals. We obtain the photon statistics of the quantized field by ‘‘measuring’’ the atomic collapse of a single revival–a technique which might be applicable in the realm of the one-atom maser.

A semiclassical theory of hyper-Raman scattering and three-photon resonant ionization via the coupled density-matrix and Maxwell equations is presented. A simplified three-level atom model is obtained, which includes two-photon resonant pumping and time-dependent photoionization rates. We consider conditions typically encountered in atomic vapors to simulate numerically the pulse propagation. A strong depletion of the photoionization probability in the hyper-Raman field-saturation regime is predicted.

We derive reduced field equations describing two cases of optical cavities driven by an external coherent field, taking into account the influence of transverse effects. For the passive-cavity case, we focus on the transistor characteristic and the onset of optical bistability. We prove that, depending on the sign of the detuning, different equations are needed. A global description of the field is possible in terms of a generalized Ginzburg-Landau equation, unless the detuning is finite and positive. That case requires a modal expansion. Furthermore, the good-cavity limit is regular, implying the same differentiation according to the sign of the detuning. For the active-cavity case, the same dependence on the sign of the detuning is found. A global description is obtained only for negative detunings. The good-cavity limit is described by a unique equation for all detunings.

We examine the mutual coherence and phase dynamics of two solid-state lasers, generated adjacent to each other in a single Nd:YAG rod. The coupling of the lasers is varied by changing the separation of the pump beams. A model is formulated to interpret the experimental results, and theoretical predictions are obtained that are in excellent agreement with the measurements.

We show that it is possible to amplify a beam of light in such a way that less noise is added to the beam than would be added by a quantum-noise-limited amplifier. This result can be interpreted in terms of a filtering mechanism that makes it possible to reduce the effective noise bandwidth of the amplifier.

We study statistical properties of quantum superposition states (Schrödinger-cat states) amplified by phase-sensitive (squeezed) amplifiers. We show that the phase-sensitive amplifier with a properly chosen phase can preserve quantum coherences and nonclassical behavior of the Schrödinger-cat-state input even for a gain factor G larger than 2. In particular, we show that for an even coherent state (CS) phase-sensitive amplifiers can preserve squeezing for G>2 but simultaneously in the process of amplification the noise added by the amplifier leads to a rapid increase of fluctuations in the photon number. Because of the finite maximum degree of squeezing obtainable for the even CS the maximum gain factor ${\mathit{G}}_{\mathit{m}}$ for which squeezing can still be observed in the output state is finite. The phase-sensitive amplifier with a properly chosen phase can also reduce fluctuations in the photon number of the initial even CS. Nevertheless, one cannot amplify the initial even CS with super-Poissonian photon statistics into the state with sub-Poissonian photon statistics.

Previous investigations of stimulated Raman scattering in a multipass cell have considered the amplification of a Stokes input pulse. They found that a simple plane-wave transient theory, appropriately scaled to include the multiple passes and focusing, matched experimental data well. In this paper, we investigate growth from spontaneous emission in a ${\mathrm{H}}_2$ Raman multipass cell. We find that a fully-quantum-mechanical scaled plane-wave theory describes the growth from spontaneous emission well in the high-gain limit. However, in the low-gain regime there is a significant increase in the Stokes output which is not predicted by the scaled plane-wave theory.

A phase quasi-integral for stimulated Raman scattering (SRS) is found. The relative phase of laser, Stokes, and polarization waves is found to be nearly conserved during their propagation in Raman media. Due to this quasi-integral, the temporal statistics of solitonlike pulses in a depleted pump is defined by phase statistics in the linear stage of SRS.

We study the linewidth of a one-photon laser through the approach of the two-time correlation function. Our numerical calculations cover the regions of below, near, and above threshold. Well below threshold, the laser linewidth decreases linearly with increasing linear gain. Near and above threshold, in comparison with the approximate linewidth given by the phase-diffusion coefficient at the mean photon number (which is inversely proportional to the laser intensity—the Schawlow-Townes formula), we find that the laser intensity fluctuations increase the laser linewidth and that the Schawlow-Townes formula is valid only when the mean photon number is large and the photon-number variance is much smaller than the square of the mean photon number. Near threshold, the laser linewidth can be twice as large as that given by the phase-diffusion coefficient at the mean photon number (i.e., twice as large as that given by the Schawlow-Townes formula).

A perturbation theory is developed to investigate the effects of various perturbations on soliton propagation down an optical fiber. The theory is formulated within the ‘‘natural’’ framework of inverse scattering theory. The perturbative effects of third-order dispersion, the soliton self-frequency shift, bandwidth-limited gain, periodic modulation, and stochastic fluctuations are analyzed in detail. In each case, the analytic results presented here are in excellent agreement with simulations carried out here and elsewhere.

We study the spin-exchange frequency shifts and line broadening of the deuterium maser in the temperature range from 0 to 10 K. We consider both a version operating on the β-ε transition at B=3.0 μT and one operating on the β-δ transition at B=3.9 mT. For the first transition, a comparison is made with our earlier results based on the degenerate-internal-states approximation and its first-order corrections [E. Tiesinga, H. T. C. Stoof, B. J. Verhaar, and S. B. Crampton, Physica B 165&166, 19 (1990)]. We find cusp structures due to channel thresholds and also resonance structures, both of which disappear almost completely after thermal averaging in the temperature range considered.

The effect of smoothly varying transverse gain and refraction profiles on x-ray laser coherence is analyzed by modally expanding the laser electric field within the paraxial approximation. Comparison with a square transverse profile reveals that smoothly varying profiles generally lead to a greatly reduced number of guided modes and a consequent improvement in transverse coherence length. However, the refractive defocusing responsible for enhanced coherence can also significantly degrade the coherent power of plasma x-ray lasers based on amplified spontaneous emission. A critical value of the Fresnel number is indicated, below which the coherent power rapidly decreases as refractive defocusing is increased. A parameter study of transverse coherence for current or planned x-ray laser experiments is provided. Comparison with ray-optics scaling laws for transverse coherence length and coherent power is made. An optimal coherent energy output of nearly 0.5 mJ in 100 psec is determined in Ni-like Ta at a wavelength of 45 Å for a saturated single-stage x-ray laser. A favorable comparison with coherent energy requirements for holographic imaging of biological samples is indicated.

The basic tool in quantum optics for the description of atomic systems interacting with coherent and incoherent radiation fields is the atomic density matrix governed by the master equation. In the present paper we apply standard condensed-matter nonequilibrium many-body methods to the problem of a two-level atom driven by an external laser field and relaxing by interaction with the radiation field. We recover the well-known dressed-atom picture and, in particular, we present an alternative derivation of the master equation for the atomic density matrix which allows simple generalizations.

An analysis of the effects of detuning and the superposition angle on amplitude-squared (AS) squeezing is presented for the one- and two-photon Jaynes-Cummings model (JCM) using coherent and squeeze inputs. In the one-photon JCM for squeezed inputs, it is shown that the degree of AS squeezing increases as the detuning increases. The two-photon JCM, on the other hand, displays this characteristic only for coherent input in a small range of values of the detuning. The superposition angle affects the degree of AS squeezing more significantly for a detuned field than for a tuned one. The behavior of AS squeezing becomes independent of the value of the superposition angle in both the models for large initial average photon number, n¯, with any value of detuning and for large detuning with any value of n¯.

Routes to regenerative spiking periodic oscillations are discussed in a delayed-feedback optical bi- stable system consisting of a laser diode interferometer. The observed oscillations have almost the same fundamental period as the delay time or the period of its subharmonics. The dependence of bifurcation routes on the delay time and other control parameters is investigated. The linear stability analysis of the dynamical equation is conducted. The obtained mode distributions show good agreements with the spectral distributions of these spiking oscillations. Numerical simulations for several steady states are also given. They show that such spiking oscillations indeed exist in certain parameter regions.