The phase-space evolution for the instabilities in a ${\mathrm{CO}}_2$ laser with an intracavity saturable absorber is investigated experimentally. The different scenarios corresponding to limit cycles, homoclinic orbits and cycles involving two unstable points, and chaotic behavior are investigated. A theoretical analysis of the experimental results is sketched out.

A recently proposed nonlinear kinetic theory for a dense fluid of square-well molecules reveals the existence of two temperature scales, one associated with kinetic energy and the other with potential energy. The scales are coupled through conservation of energy and, for nonequilibrium states, the temperature scales are not identical. The distinction between the temperature scales affects the value of the bulk viscosity.

High-resolution x-ray scattering measurements of the smectic-C phase of the polymeric liquid crystal, C-6 polysiloxane, show that the smectic-C tilt angle ${\phi }_p$ decreases continuously upon decreasing temperature. This behavior, opposite to that observed in monomeric liquid crystals, is caused by stiffening in the polymeric backbones and spacers.

An examination of the fluorescent process in simple and detailed models of multilevel atoms, expressed in terms of the parameter $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$ where $P_{\mathrm{ij}}$ and $C_{\mathrm{ij}}$ are, respectively, the photoexcitation rate and the collisional excitation rate in the pumped resonance transition i-j, shows that three distinct regimes exist over the full range of this parameter which may be usefully exploited. The regimes are defined by I, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≲1; II, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≫1, $P_{\mathrm{ij}}$≪$C_{\mathrm{ki}}$; III, $P_{\mathrm{ij}}$/$C_{\mathrm{ij}}$≫1, $P_{\mathrm{ij}}$≫$C_{\mathrm{ki}}$, where $C_{\mathrm{ki}}$ is the collisional rate populating the source level i. Regime I is characterized by sensitivity of fluorescent-fluorescent line intensity ratios to the photoexcitation rate $P_{\mathrm{ij}}$. Regime II is characterized, on the other hand, by insensitivity of these line ratios to $P_{\mathrm{ij}}$. If regime III is reached, even fluorescent-nonfluorescent line ratios become independent of $P_{\mathrm{ij}}$. A concrete application of the analysis has been made to the resonant photoexcitation of a carbonlike ion.

An optical arrangement of three reflectors is shown to exhibit antilocalization of light. Situations in which this phenomenon can be used to create a form of invisible paint are discussed.

A novel relativistic quantum theory of the free-electron laser is formulated using the Dirac equation. It is shown that the theory has the correct classical limit. It is predicted that for two-stage free-electron lasers, quantum noise can be comparable to the classical noise due to the thermal spread of the beam or the random initial distribution of electrons in phase.

We show that pulses of electromagnetic radiation with a hyperbolic-secant envelope and a hyperbolic-tangent frequency sweep are capable of exciting an inversion line shape in a collection of two-level absorbers that is highly insensitive to optical density. This is not true of the hyperbolic-secant π pulse (with no frequency modulation) which undergoes significant reshaping as it propagates. The analysis is based on numerical solutions of the coupled Maxwell-Bloch equations in both the plane-wave and paraxial approximations. We also show an additional insensitivity of the inversion profile to finite relaxation times ($T_2$) that approach the pulse width.

The modulational instability of an arbitrarily-large-amplitude electron cyclotron wave along the external magnetic field has been investigated, taking into account the relativistic electron quiver velocity and the relativistic ponderomotive force. Three types of plasma slow responses have been considered and a parameter study of the instability growth rates has been carried out.

We have measured the shift of the He ii 4685.7-Å line at electron density ranging from 2.5×${10}^{17}$ to 18.8×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and electron temperature between 8 and 10.5 eV. The plasma was produced in a Z-pinch discharge. Systematic red shifts linear in density are observed. The experimental results are in agreement with the best-fit curve of earlier results by Pittman and Fleurier obtained at lower electron densities and temperatures.

Results are reported for the dynamic structure factor S(kω) for ions in the hitherto theoretically inaccessible regime of strongly coupled partially degenerate hydrogen plasmas where the electron-ion interaction is not weak. Results from density-functional theory and molecular dynamics have been used to provide a rigorous approach which avoids linear-response approximations or the construction of pseudopotentials. The results are discussed in terms of a microscopic theory and a hydrodynamic model. Values of the sound velocity, thermal diffusivity, the specific-heat ratio, and the viscosity for these plasmas are reported.

We present phase diagrams of the Toda oscillator x¨+dẋ+$e^x$-1=f cos(ωt) showing the loci of local bifurcations of periodic orbits in the (ω,f) parameter plane at d=0.05. They indicate a specific recurrent structure in the bifurcation set which is typical for nonlinear oscillators and closely connected to the nonlinear resonances of the system.

The continuum theory of a collection of self-avoiding D-dimensional manifolds with fixed connectivity embedded in d dimensions is considered. The self-avoiding interaction between multiple points of a manifold is shown to be screened in the presence of other manifolds. The screening length and the mean-square distance between two points of a manifold are derived to decrease with the manifold density ρ according to ${\rho }^{\mathrm{-}(D+2)/2\left(d\mathrm{-}D\right)}$ and ${\rho }^{\mathrm{-}\left[4D\mathrm{-}\right(2\mathrm{}\mathrm{-}D\left)d\right]/2\left(d\mathrm{-}D\right)}$, respectively.

A relation between the kernel of a quantum system in Feynman’s path-integral theory and the transition probability of the corresponding Markov process, with the diffusion coefficient rotated to the imaginary axis, is obtained in the framework of stochastic mechanics. If a stationary state is considered, the relation reduces to a form relating a Euclidean (i.e., imaginary time) quantum theory to a Markov process.

Isotope shifts have been measured in the velocity-dependent total cross sections of the $m_1$=1 magnetic substate of He(3 ${}_{}{}^3{}_{}{}^{}$P) formed in low keV ${\mathrm{He}}^{+}$+${\mathrm{H}}_2$ or ${\mathrm{D}}_2$ collisions. Similar isotope shifts have been predicted on theoretical grounds and observed in ion-atom collision experiments, where united-atom rotational coupling is the primary excitation mechanism. By extending the basic theoretical ideas to ion-molecule collisions, we can interpret our measured shifts as resulting from rotational coupling within the triatomic ${\mathrm{HeH}}_2^{+}$ complex.

We show how it is possible to systematically eliminate, with little resulting error, all ‘‘free-free’’ and ‘‘bound-free’’ exchange integrals needed to implement electron scattering calculations with algebraic variational techniques, such as the Kohn method. This elimination is rigorous within the framework of the separable approximation for exchange interactions and follows from certain invariance properties of the scattering wave function. The procedure is illustrated for the case of $e^{\mathrm{-}}$+He and $e^{\mathrm{-}}$+H scattering in the static-exchange approximation.

Cross sections for the photoionization of excited nf states in the Cs isoelectronic sequence show simple monotonic behavior for neutral Cs but considerable structure for the ions due to the collapse of the nf orbitals. This is the first demonstration of orbital collapse in highly excited states.