Systems that exhibit stimulated Raman scattering in the transient limit have long been the subject of theoretical and experimental study, and recent experimental developments have made possible the observation of the long-distance evolution of these systems. These systems are integrable using the inverse scattering method; however, in contrast to the usual behavior in integrable systems, solitons do not dominate the long-distance behavior. Instead, solitons are transient, and self-similarity appears in the long-distance limit. In this paper, the similarity solutions of the equations which describe stimulated Raman scattering are first reviewed from a physical standpoint. Inverse scattering theory is then used to show that given physically reasonable initial data in which the pump and Stokes waves have no linear frequency mismatch, the solution will converge toward a self-similar solution. These results are confirmed by a numerical comparison of the solution of the transient, stimulated Raman-scattering equations to the appropriate self-similar solutions. The length scale over which convergence occurs and the transient generation of solitons are observed. From a physical standpoint, the appearance of self-similarity rather than solitons in the long-distance limit can be attributed to the presence of memory in the Raman-active medium. Other systems with memory also exhibit self-similarity, and the results which are described here may have applications to a wide array of optical systems with memory. An experiment which could observe self-similarity is described.

We report experimental and theoretical observations of a period-doubling route to chaos in a semiconductor laser with optical feedback. Increasing the feedback produces a quasiperiodic route to chaos, manifested as a catastrophic increase in the laser linewidth. Under certain conditions, frequency locking occurs in preference to quasiperiodicity, and then period doubling appears. Both phenomena are explained as interactions between the external cavity modes and the laser relaxation oscillations.

Resonant photopumping of Be-like Mg ix ions by Li-like Al xi line radiation has been studied in pulsed-power-driven plasmas as a possible approach to achieve laser action in the extreme-ultraviolet wavelength region. An Al x-pinch or z-pinch plasma imploded by a 0.5-TW pulsed power generator produced intense line radiation at 48.338 Å. A separate Mg z-pinch plasma, driven by the same pulsed power generator, was created in parallel with 1 cm separating the two plasmas. Evidence for fluorescence (resonant scattering) was the appearance of 48.340-Å resonance line emission from the 4p level of Mg ix ions due to photopumping by the Al xi line radiation at 48.338 Å. Fluorescence may also have been observed on the Mg viii line at 52.395 Å, photopumped by Al xi line radiation at 52.446 Å. Both Al and Mg plasmas were characterized in the experiments. Improvements to the pump geometry required to achieve gain on the Mg ix line at 228 Å are also discussed.

A self-consistent theory is used to derive the frequency shift presented by the oscillating mode in a cavity that contains a photorefractive crystal. A long-time-limit theory has been used to get the steady characteristics of the cavity field. The problem of the weak-field approximation is avoided. This approximation is useless in the case studied because the interaction along the crystal is so strong that one has to take in account the intensity exchange occurring inside the material between the pump and oscillating beams (two-wave mixing). We have fully analyzed the influence of the transverse nature of the beams on the intensity exchange in the two-wave mixing situation. In the photorefractive resonator case, the frequency shift of the oscillating beam is expressed in terms of a ratio that presents poles. The dependence on the problem parameters of these poles is studied and a perturbative method is developed; it is based on the smallness of the transverse overlap between the pump and cavity modes. An analytical expression for this frequency shift is obtained.

The time evolution of squeezing in the two-photon interaction of a Rydberg atom with two nondegenerate modes of an ideal cavity is analyzed. The study compares the results from the two representations of the atom by a three-level system and an effective two-level system. We find the time evolution of the squeezing in the two systems to be different, including the regimes where the dynamics of the population are similar.

A high-power laser radiation, with frequency ${\mathrm{\omega }}_1$ and wave vector ${\mathit{k}}_1$z^, propagating through a semiconductor produces a second-harmonic longitudinal current at 2${\mathrm{\omega }}_1$ and 2${\mathit{k}}_1$z^. When a wiggler magnetic field (0,${\mathit{k}}_0$z^) is simultaneously present in the system, the J×B force on the electrons produces a transverse second harmonic current at 2${\mathrm{\omega }}_1$ and (2${\mathit{k}}_1$+${\mathit{k}}_0$)z^, driving second-harmonic electromagnetic radiation. For a specific value of wiggler wave number ${\mathit{k}}_0$=${\mathit{k}}_{0\mathit{c}}$ the phase-matching conditions for the process are satisfied, leading to resonant enhancement in the efficiency of energy conversion. ${\mathit{k}}_{0\mathit{c}}$ decreases with the frequency ${\mathrm{\omega }}_1$ of the laser.

We investigate properties of a two-level atom coupled to a single cavity mode, and driven by a strong, in general off-resonance, external field. The cavity field is tuned to resonance with a Mollow sideband. We show that the steady-state atomic population may be highly (nearly totally) inverted, a phenomenon forbidden in semiclassical theory, and that a strong enhancement of the resonance fluorescence results. This system is suggested as an alternative approach to create the atomic inversion necessary for laser or maser generation without using additional atomic levels. We also investigate properties of the cavity field, derive an analytical expression for the photon number distribution in the good cavity or strong-coupling limit, and discuss the conditions under which this system acts as a single-atom dressed-state laser.

Further interference experiments have been carried out with the two signal beams emitted from two coherently pumped parametric down-converters when the two idler beams are aligned. Because of the quantum entanglement between signal and idler photons produced in the down-conversion, it is found that the visibility of the interference of signal photons can be controlled by insertion of differential time delays between the idler photons.

The destructive interference between the three-photon and the third-harmonic one-photon absorption in the vicinity of the 6s[3/2${]}_1$ state of Xe has been studied in the resonantly enhanced multiphoton ionization via nf states, through the cancellation of the nf, J=2 resonances of the spectrum, accessible by four-photon absorption. The gas-pressure, i.e., phase-matching, dependence of the three-photon detuning range from the 6s[3/2${]}_1$ state for which cancellation occurs has been investigated in one- and two-color experiments, including positive detuning from this state in positively dispersive regions. For obtaining cancellation, the theoretically predicted requirement of optically thick medium at the third-harmonic frequency is corroborated by present observations for negative detunings. The different cancellation behavior of the nf[3/2${]}_2$ and nf[5/2${]}_2$ states observed indicates the dependence of the effect on the atomic parameters of the coupled four-photon resonance. The experimental results are found to be in partial agreement with existing theoretical models.

The angular distribution of the ion fragments after multiphoton ionization of diatomic molecules shows a pronounced anisotropy. Fragments are detected mainly along the direction of the laser polarization, as is shown for iodine in this paper. We have performed a double-pulse experiment to clarify the underlying mechanism. It shows that the anisotropy cannot be explained in terms of a variation of the ionization rates with the angle between the electric field and the molecular axis. Instead, the anisotropy is caused by the deflection of the ion fragments in the strong field due to the molecular polarizability. Although the molecules are frozen in space on the time scale of the laser pulse, they gain enough angular momentum to affect the trajectories of the fragments. Classical trajectory calculations support this explanation.

We study numerically the photoionization of a one-dimensional model atom, with a very-short-range potential, in the Kramers-Henneberger frame. In the range where suppression of ionization is found, the ground-state depletion follows a well-fitted exponential decay. The decay rate has been examined for different values of the laser frequency and for different intensities. Comparisons with existing analytical predictions are made where appropriate.

The differences between macroscopic (all time or entire ensemble average) and submacroscopic (partial time or partial ensemble average) fields of micromasers with non-Poissonian pumping are discussed. A formula to calculate the steady-state density matrix of the macroscopic field is derived. The photon statistics, average photon numbers, and photon-number variances of the macroscopic field, together with those of the submacroscopic fields, are obtained and compared. The photon statistics of a special submacroscopic field are almost the same as those of the macroscopic field.

We consider second-harmonic generation within a laser cavity. García-Fernández et al. [Quantum Opt. 2, 49 (1990)] found that large-amplitude squeezing may be obtained in the fundamental output if the cavity loss rates are high compared to the atomic decay rates. We extend their calculations, taking fully into account the phase diffusion of the laser field, and considering different dynamical regimes. We obtain large-amplitude squeezing in the second-harmonic output if the cavity loss rate at the second harmonic is high compared to the atomic decay rates. However, the cavity loss rate at the fundamental may still be slow compared to the atomic loss rate.

Rabi sidebands of the Na atomic vapor excited by a resonant-pulsed-laser beam were observed in the forward-direction radiation. While the laser power scans over a factor of 10, the change of Rabi shift is much less than what is expected by the two-level dressed-atom model. Therefore a multilevel dressed-atom model is developed to calculate the levels of the dressed Na atom, and the influence of the time evolution of the laser power is also taken into account in counting the real observable spectrum. After considering all these factors, the final calculated data fit the experimental results satisfactorily.

The interaction Hamiltonian for the degenerate parametric amplifier leads to an eigenvalue equation which can be solved. The solution is used to construct the propagation kernel for the state vectors. We can then follow the evolution of the squeezed variable and its conjugate one. Also the changes of entropies during the process can be followed without difficulties.

We investigate the nonlinear dynamics of temporal pattern formation in a driven and damped nonlinear-optical system. The patterns result from the growth of modulations in the optical field which circulates inside a nonlinear dispersive fiber ring with bandwidth-limited gain and an external injected signal.

We investigate the influence of pump bandwidth and pump intensity noise on the quantum-noise properties of lasers based on a Raman atomic-gain medium, which recently have been predicted to emit narrow-bandwidth, sub-shot-noise light. We show that, using finite-bandwidth pump light, the predicted limit to the laser bandwidth can still be well below the value given by the Shawlow-Townes formula and much smaller than the input bandwidth. The laser intensity noise is shown to be relatively insensitive to input phase noise as long as the Rabi frequency on the lasing transition is large compared to the bandwidth. On the other hand, even small amounts of pump amplitude noise tend to increase strongly the laser spectral bandwidth, especially in the high-intensity limit. Including dynamic pump-noise reduction through multilevel atomic cycling in our model leads to a Mandel Q parameter value even below Q=-1/2, together with a significant enhancement of the output intensity-noise squeezing.

We investigate the prospects of a Fabry-Pérot interferometer for atomic matter waves.

We show that electron- and proton-impact ionization cross sections for highly stripped heavy ions can be deduced from the projectile-electron-loss cross sections determined by collisions with a ${\mathrm{H}}_2$ and a He target. We measure electron loss for 100- and 380-MeV/u ${\mathrm{Au}}^{52+}$, and 405-MeV/u ${\mathrm{U}}^{86+}$ in ${\mathrm{H}}_2$ and He targets, and extract the electron- and proton-impact ionization cross sections. Our results are compared with calculations and with channeling experiments.

We derive the integral form of the Schrödinger equation taking the Green function originating from the perturbation and prove the equivalence with the free representation. The equation is applied to a class of strong perturbing potentials of the form λw(x)g(t) with λ→∞. The method of stationary phase applied in this case gives the first terms of an asymptotic series for the probability amplitudes to find the system in one of the states of the unperturbed Hamiltonian, and these are shown to go to zero in the considered limit.