We describe a theoretical model that shows how stimulated Brillouin scattering (SBS) is initiated by thermally excited acoustic waves distributed within a Brillouin-active medium. This model predicts how the SBS reflectivity, Stokes linewidth, and fluctuations in Stokes intensity depend upon the laser intensity and upon the physical properties of the SBS medium. This model also leads to the prediction that the value of the single-pass gain (i.e., G=gIL) at the threshold for SBS is not a universal number, but depends upon the laser frequency and on the properties of the SBS medium. For typical organic liquids at room temperature, G is in the range 20–25.

Different aspects of the interaction of a three-level atom with a single-mode radiation field are studied inside a cavity with damping. It is demonstrated that two-photon transitions emerge from cascade one-photon transitions by increasing the detuning parameters of the levels. It is also shown that a simulation of the two-level atom with one-photon transitions can be achieved by changing the detuning parameters adequately. In all cases, the influence of cavity damping is examined. Finally, we point out that the second-order field correlation function approaches its minimum value for t→∞ in some cases.

We calculate the spectrum of third-harmonic generation (THG) for multimode fundamental input fields. We consider input fields from (1) a laser with gain on several cavity modes, (2) pulses with short temporal duration, and (3) frequency-modulated input fields. The effects of phase modulation in the nonlinear medium on the spectrum of the THG field are considered. Using the estimates by Miles and Harris [IEEE J. Quantum Electron. QE-9, 470 (1973)] for the nonlinear susceptibilities ${\mathrm{\chi }}^{\mathrm{}\left(3\right)\mathrm{}}$(-3ω;ω,ω,ω) and ${\mathrm{\chi }}^{\mathrm{}\left(3\right)\mathrm{}}$(-ω;ω,-ω,ω) in alkali-metal vapors, we find that phase modulation can profoundly affect the efficiency and the spectrum of the THG. Generally, the self-phase modulation of the fundamental will tend to reduce the phase matching of an intense fundamental field and the third harmonic and thereby lower the conversion efficiency. New frequencies not contained in the set of frequencies ${\mathrm{\omega }}_{1\mathit{i}}$+${\mathrm{\omega }}_{1\mathit{j}}$+${\mathrm{\omega }}_{1\mathit{k}}$, where {${\mathrm{\omega }}_{1\mathit{i}}$} are frequencies in the fundamental laser spectrum, are created even at relatively low conversion due to phase modulation. Effects of cross phase modulation are also studied.

We present the nonlinear theory for lasing without population inversion in the degenerate Λ-type quantum-beam laser by using the density-operator method. The master equation for the degenerate quantum-beat laser is derived, from which the equation of motion for the mean photon number is obtained. The conditions for lasing without population inversion are discussed, which are the same for linear and nonlinear theories. The corresponding Fokker-Planck equation is obtained, and the possibility of diffusion coefficient reduction is discussed.

We show that in a double two-photon correlated-spontaneous-emission laser, generation of squeezed light is compatible with atomic inversion by using the atomic coherence between two lower levels. The resulting device can yield, via resonant stimulated amplification, bright beams of squeezed light.

In this paper the pulse solutions to the pair of partial differential equations governing light in a nonlinear, birefringent fiber are considered. A direct proof of the nonintegrability of the equations is given and attention is restricted to the stationary solutions. These are parametrized in terms of the physical conserved quantities and the relationship between the conserved quantities indicates when certain pulse solutions become unstable. This theoretical prediction is tested against numerical simulations.

The possible frequency-dependent diffraction loss mechanisms and the associated asymmetries of the output power versus frequency profiles are theoretically and experimentally investigated in equally mixed two-isotope gas lasers. It is shown that the evolution of resonant diffraction losses due to population lenslike effects is unchanged with respect to the single-isotope case. However, the resonant diffraction losses due to saturation lenslike effects in two-isotope systems are shown to exhibit three different possible behaviors, depending on the relative values of the homogeneous width and the isotope shift of the transition and the free spectral range of the laser cavity. In particular, it is shown that in the case where the homogeneous width of the transition is smaller than the half isotope shift, as long as the free spectral range of the cavity is larger than the isotope shift, the output power profile exhibits two reversed asymmetries, for the center and the wings of the profile. The case of usual ring-laser gyroscopes is also investigated and shows that in this case the output power is more important on the high-frequency side than on the low-frequency side, independently of the nature of the predominant lenslike effect. In every case, a good agreement is obtained between the experimental profiles and the theoretical results, computed either from a third-order perturbative calculation or a high-intensity exact theory. Such a high-intensity calculation is shown to be necessary to make quantitative comparisons between experiments and theory in ring-laser gyroscopes.

Intense light incident on a dense-gas–dielectric interface, from the dielectric side, is reflected because of the combined effect of the discontinuities in the index of refraction at the interface and at the transition region in the gas where the degree of atomic saturation changes abruptly. This latter discontinuity gives rise to a self-reflected wave. At low intensities this self-reflected wave is weak, the problem is linear, and the net reflected wave intensity taken as a function of frequency has a simple shape that should allow measurement of the hitherto undetected self-induced frequency shift in a collision-broadened gas at an absorption resonance. Calculations show that in the weak intensity regime, r’’, the imaginary part of the reflection coefficient, is quasi-Lorentzian and shifted by an amount comparable to its width. At high light intensity r’’ broadens, shifts, and distorts. The distortion, which nonuniformly modulates the Lorentzian shape, comes from an interference of the forward and self-reflected waves. In the wings of the resonance line the self-reflected wave can be neglected, and the shape of r’’ although not distorted is shifted from where it would be if there were no local field correction.

An analytic momentum-space wave function for an electron in both laser and static uniform electric fields is presented. It is used to obtain analytic multiphoton detachment cross sections in a static, uniform electric field which include effects of static-field-induced electron-photon interactions. These general results are not restricted to weak laser intensities or to weak static-field strengths and depend only on (a) the electric dipole approximation and (b) the approximation that final-state electron-atom interactions are ignored. Four specific predictions of our general formulas for the most interesting case of linearly polarized light polarized along the static-field direction are presented for weakly bound electrons initially in an s state. First, the effects of a weak static electric field on N-photon detachment cross sections near threshold are shown to be described by two modulation factors, one for odd N and one for even N, which depend only on a scaled energy. Second, for photodetachment in a static electric field, effects of static-field-induced electron-photon interactions are demonstrated. Third, the lifetime against field ionization is presented. Fourth, the cross section for electric-field-induced stimulated emission is presented. Numerical results for the latter three effects are presented for the ${\mathrm{H}}^{\mathrm{-}}$ ion. The simpler case of circularly polarized light directed along the static-electric-field direction is treated briefly. In particular, we show for this case that the static- and laser-field effects are uncoupled and that the near-threshold, weak static-electric-field modulation factors for the N-photon detachment cross sections are dependent on N.

We develop a quantization procedure for treating the propagation of light. This formalism is particularly effective in a dispersive nonlinear medium characterized by its macroscopic linear and nonlinear polarizability. We demonstrate it by analyzing the propagation of light in a multimode degenerate parametric amplifier.

The master equation for a dc-pumped degenerate Josephson parametric amplifier is derived. It is shown that the Wigner distribution representation of this master equation can be approximated by a Fokker-Planck equation. By using this equation, the dynamical behavior of this degenerate Josephson amplifier with respect to squeezing of the radiation field is investigated. It is shown that below threshold of parametric oscillation, a squeezed vacuum state can be generated, and above threshold a second bifurcation point exists, where the device generates amplitude squeezed radiation. Basic relations between the achievable amplitude squeezing, the output power, and the operation frequency are derived.

We present results on the nonlinear-optical response for a series of dielectric particles having nanometer sizes that are coated with a metallic shell. Using the freedom of changing particle shapes and coating thicknesses, we optimize the threshold intensity for intrinsic optical bistability. The metallic shell creates an enhanced local field in the nonlinear core. We report threshold intensities for silver-coated CdS as low as 12 W/${\mathrm{cm}}^2$.

We calculate the time-dependent spectrum of spontaneously emitted light from a coherently excited diatomic molecule. We show that this spectrum provides a tool for direct observation of the atomic vibrations in the excited electronic state of the molecule, and that the finite time and frequency resolution inherent in any experiment does not destroy all information about the time-dependent shape of the molecular wave packet.

The dressing of a hydrogen atom by a single-mode linearly polarized laser, in the high-frequency approximation, has been shown to produce bound states with severely reduced binding energies in the high-intensity limit. The width of the ground state, under the same conditions, has also been shown to be small compared to its binding energy for easily realizable frequencies. The effect of a less-than-ideal laser has not been considered previously. We investigate the effect of a multimode laser with fixed-mode amplitudes and uncorrelated phases. We find that, in general, the binding energy is reduced and in some cases probably eliminated entirely.

The linear theory of the correlated-emission laser (CEL) is studied using the quantum-mechanical definition of the phase of the electromagnetic field recently introduced by Barnett and Pegg [J. Mod. Opt. 36, 17 (1989); Phys. Rev. A 39, 1665 (1989)]. From the master equation for the density matrix of the field, a Fokker-Planck equation for the phase probability function is derived, and the phase properties of the CEL discussed. The Adler equation and the equation of motion for the variance of the phase difference are derived. The Fokker-Planck equation satisfied by the phase probability function is compared with the corresponding equations for the P, Q, and Wigner quasiprobability distributions, specialized to the case when amplitude fluctuations are negligible. We show that the phase probability function and the Wigner function satisfy the same equation, and conclude that, of the three quasiprobability functions studied, only the Wigner function is reliable for calculating directly the phase properties. The commonly used P function overestimates the laser linewidth by a factor of 2.

We point out that the phase-diffusion rate in an amplifier or attenuator is not proportional to the phase-diffusion coefficient in the Glauber P nor the antinormal-ordering Q distribution. It is only proportional to the phase-diffusion coefficient in the Wigner (W) distribution. We also find that, for a phase-insensitive oscillator, the steady-state phase-diffusion coefficients in the P, W, and Q distributions must be identical to each other.

Previous calculations of the bound state of H in an intense linearly polarized laser field in the high-intensity limit are used to investigate similar bound states of ${\mathrm{H}}^{\mathrm{-}}$, He, and Li. The first two are bound in states that are simple generalizations of the one-electron results. Li is also bound, but in a different configuration.

We report the ionization of Na atoms by the simultaneous application of microwave fields of two different frequencies. We conclude that the salient features of double-frequency ionization can be readily understood. Both the hydrogenlike ‖m‖=2 states and the nonhydrogenic ‖m‖=0 and 1 states ionize when the sum of the field amplitudes, the peak field, reaches the field required for ionization by a single microwave frequency, E=1/9${\mathit{n}}^4$ and E=1/3${\mathit{n}}^5$, respectively.

A simple quantum theory of recently suggested optical techniques for ultrahigh-resolution position measurement and localization of moving atoms in beams is presented. Both the internal and center-of-mass motion are treated quantum mechanically so that the limitations on the ultimate position resolution due to atomic motion and wave-mechanical diffraction are included in the analysis. The techniques utilize a miniaturized form of Raman-induced resonance imaging in which optical fields are used to make transitions from a long-lived initial state to a long-lived final state. The final state is shifted by the spatially varying potential of an applied force field in order to correlate the atomic position with its resonance frequency. Spatially varying level shifts are obtainable by using very large Zeeman field gradients or spatially varying light shifts in a small interaction volume. This results in very high spatial resolution. The atomic transit time across the optical-field region is limited by focusing to an ideal diameter that minimizes the spatial resolution length. The results of the analysis show that nanometer spatial resolution of the initial-state position distribution is attainable. Under appropriate conditions, the final-state spatial wave function can take the form of a minimum-uncertainty Gaussian wave packet obeying ΔxΔp=ħ/2. Such states may prove useful in studying one-dimensional wave-packet motion in applied potentials.

A mode-locked soliton laser, experiencing group-velocity dispersion and self-phase modulation via a nonlinear Kerr medium in an antiresonant ring interferometer reflector is analyzed in the linearized regime. It is demonstrated that this laser can produce an ultrashort squeezed vacuum from the open port of the antiresonant ring interferometer and that the spectral linewidth of the soliton output is broadened via the coupling of amplitude and phase in the Kerr medium.