Measurements of two-photon absorption spectra have been made for the case where the exciting laser has a random-telegraph phase. The resulting spectral shapes are compared to theoretical predictions and to previous data taken with a phase-diffusing laser field [Elliott et al., Phys. Rev. A 32, 887 (1985)]. A striking dependence of the absorption spectrum on the second-order coherence of the field was observed. Using the theory for the propagation of second-order spatial coherence, we draw an analogy between diffraction and two-photon absorption which we use to interpret the two-photon absorption spectra.

The electron-atom scattering in the presence of an intense radiation field is investigated by solving the Schrödinger equation in momentum space, which facilitates the extraction of the rapidly varying part of the wave function. It can be shown that the first-order Born approximation is only a limiting situation of the general approach. The angular distributions of the scattering probability are calculated for different field strengths and some interesting points regarding the multiphoton process are also discussed.

In this paper, we present a discussion of the role that angular momentum plays in the interaction of an intense laser field with a single-electron atom. To do this, we have made a detailed analysis of how different partial waves, i.e., different angular momentum states, participate in producing the photoelectron energy, angular distributions, and harmonic generation spectra. We show that the two regimes—tunneling and multiphoton excitation—correspond to quite distinct evolution patterns across the partial wave decomposition. The natures of these patterns are particularly significant in the harmonic generation spectra and emphasize how harmonic generation is mainly produced in transitions back to the initial state. We also find that at high intensities, the photoelectron energy spectrum is composed of two different but well defined sets of above-threshold ionization peaks. These two sets are separated by a structureless region and the second set deviates substantially from the initial exponential decrease of the peak intensities versus energy. Similar features have been very recently reported experimentally.

We observe interference in the resonant microwave multiphoton transition probability between the 21s state and the 19,3 Stark state of K in a static field as a function of the duration and intensity of a microwave pulse at 9 GHz. The 19,3 state adiabatically connects to the 19f state in zero field. The ac Stark effect shifts the 21s state through a multiphoton resonance with the 19,3 Stark state during both the rising and falling edges of the microwave pulse. The transitions that occur during each traversal of the resonance lead to an interference in the net transition probability as a function of the relative phase accumulated by each state during the pulse. We measure both the frequency of the interference oscillations for different detunings from resonance and the amplitude of the fringes for different degrees of pulse asymmetry. The latter results are in complete agreement with the predictions of a Landau-Zener model for the resonance transitions.

The use of high-power ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As diode laser arrays for optical pumping of Rb vapor has been examined both theoretically and experimentally. Our studies show that large atomic polarizations can be obtained using the broad spectral output of a diode laser array if the Rb resonance line is collisionally broadened by several atmospheres of a buffer gas. The objective was to study the effectiveness of diode laser arrays as light sources for optically pumped spin-exchange polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ targets. The average Rb polarization was deduced at three different Rb vapor pressures using the polarization induced in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ buffer gas. The largest ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ polarization observed was 53% using a 20-W diode array with 1.9-nm full width at half maximum spectral width in 10.5 amagat of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. This result compares favorably with other light sources for this target. The measured average Rb polarizations are compared to theoretical calculations.

We investigate the resonance properties of ultracold ground state ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$${+}^6$Li, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$${+}^7$Li, and ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$${+}^{23}$Na collisions. The locations of various resonances and their corresponding error bounds due to the uncertainty of the interatomic potentials are presented. Also, the resonance widths are computed using rigorous coupled-channel calculations, as well as a modified version of Feshbach theory valid for strong fields.

We present an experimental study of dynamical localization as displayed by rubidium Rydberg atoms ionized by a coherent microwave field. The ionization threshold field has been measured over a wide range of initial principal quantum numbers of the atomic Rydberg states, for a fixed interaction time of atom and field, and for two different values of the frequency of the microwave. Furthermore, fixing the initial state of the atoms and the microwave frequency, we studied the dependence of the ionization threshold on the interaction time. In both types of experiments, we identify a clear signature of dynamical localization and of its gradual destruction by noise. The transition from dynamical localization to diffusionlike ionization as weak broadband noise is added to the coherent microwave radiation is illustrated. In addition, we supply experimental evidence that suggests that a subset of the noise spectrum depending on the principal quantum number of the initial atomic Rydberg state is more relevant for the destruction of dynamical localization.

We have calculated, by numerically integrating the time-dependent Schrödinger equation, the probability for ionization of a hydrogen atom in a parabolic downhill or uphill state by a half-cycle pulse. We confirm the conclusions of R. R. Jones, N. E. Tielking, D. You, C. Raman, and P. H. Bucksbaum [Phys. Rev. A 51, R1 (1995)], most notably that the probability of ionization is enhanced when the electron is pushed away, rather than scattered, from the nucleus by the pulse.

We report computational results for the time evolution of the velocity distribution P(V,t) for two-level and multilevel ‘‘Doppler’’ laser cooling. We compare results obtained from the semiclassical (SC) Fokker-Planck equation and from generalized optical Bloch equations applied to density matrices over a basis of products of internal and quantized translational states (QDM). Computer memory requirements are optimized to make large-scale QDM calculations feasible. QDM and SC agree well except for two cases: (a) atoms in the wells of the light-shift potential (with kinetic energy less than the well depth, ${\mathit{U}}_0$), and (b) atoms with recoil energy ${\mathit{E}}_{\mathit{R}}$ comparable to or greater than the natural linewidth ħΓ. Transient dips occur in P(V,t) at V=0 in QDM results due to slow cooling of atoms in the light-shift potential wells. Dips in P(V,t) occur at velocity-tuned-resonance (Doppleron) velocities but disappear over long interaction times as atoms accumulate near points where the force is zero. When ${\mathit{E}}_{\mathit{R}}$≊ħΓ, sharp peaks occur in P(V,T) at V=±${\mathit{V}}_{\mathit{R}}$ from velocity-selective population quasitrapping not previously found in a two-level transition. Sharp features in P(V,t) occur also for J→J+1 transitions with J>0, small ${\mathit{U}}_0$/${\mathit{E}}_{\mathit{R}}$, and sufficiently large detuning, from transitions between individual quantum states in the periodic potential.

We study analytically and numerically the motion of a trapped two-level ion in the presence of a resonant laser field. Using a semiclassical description, we find that for sufficiently strong laser fields atomic motion becomes chaotic for a wide range of parameters and initial conditions. The traces of chaotic motion are reflected in the population inversion of the trapped ion, and thus could be observed by using the quantum jump technique.

We have measured the radiative transition rate of ${\mathrm{Eu}}^{3+}$ complexes in polystyrene films on various dielectric substrates. Both inhibition and enhancement of the transition rate are observed, depending on the refractive index of the substrate and thickness of the film. This is explained in terms of local photon mode amplitudes.

We report on the observation of spatial modifications of a weak beam copropagating with a strong beam due to Raman-assisted cross phase modulation. This effect, due to the interference between nonlinear polarizations associated with the third-order susceptibility, is enhanced when the difference between the frequencies of the incident beams is resonant with the frequency of a vibrational mode of ${\mathrm{CS}}_2$. In principle, the phenomenon may be observed in a large variety of materials and can be exploited in applications such as spatial soliton switching.

It is shown that quantum-nondemolition-mediated feedback is able to preserve the interference fringes of the superposition of macroscopically distinguishable quantum states.

We introduce and study the properties of a class of coherent states for the group SU(1,1)×SU(1,1) and derive explicit expressions for these using the Clebsch-Gordan algebra for the SU(1,1) group. We also derive a phase space representation based on pair coherent states rather than the standard harmonic-oscillator coherent states. We discuss the utility of the resulting ‘‘bi-pair coherent states’’ in the context of four-mode interactions in quantum optics.

A method for construction of the k orthonormalized quantum eigenstates of the higher powers ${\mathit{a}}^{\mathit{k}}$ of the quantum-annihilation operator a is proposed, and their physical meaning is explored. Nonclassical properties of these quantum eigenstates are studied and the main results are as follows: (1) All of the eigenstates can be expressed as a linear superposition of k quantum-coherent states; (2) all of them are generalized quantum-coherent states; (3) for k≥3, they have the Nth-order quantum squeezing for N=mk+k/2 (m=0,1,2, . . .) and even k, but no Nth-order quantum squeezing for other values of N and k; (4) for k≥3, all of them exhibit the lowest- and higher-order quantum antibunching.

The gap 2π pulse or gap solitary wave of self-induced transparency at an inhomogeneously broadened line of a resonant Bragg periodical structure has been found theoretically as an exact solution of the coupled-mode Maxwell-Bloch equations. In the case of a slight violation of the Bragg condition at exact two-level resonance, the analytical solution for the gap 2π pulse with phase modulation has been obtained. Furthermore, the existence of an oscillating pulse that periodically changes in amplitude and in the sign of its velocity has been numerically shown.

Analytical solutions for the beam intensity, interferogram, and instantaneous phase are found for a ring laser with backscatter. The harmonics of these signals form geometric progressions, whose ratios depend differently on pumping, pulling, and the net backscatter phase. The latter phase depends on the time-reversal symmetry of the scatterers and on their location. We also report confirmatory results in the Canterbury ring laser system, with a quality factor up to 7.5×${10}^{10}$ and a present frequency resolution of 140 nHz, and where thermal changes in the net backscatter phase dominate other causes of drift.

We report on an experimental observation of quantum interference between two dressed states created by a coherent pumping laser in an electromagnetically induced transparency. In a Λ-type three-level atomic system in rubidium vapor, we reduce the Rabi frequency of the pumping laser in one arm down below the spontaneous decay rate of the common excited state and still observe a narrow dip with subnatural linewidth in the absorption curve of a probe beam in another arm. This clearly demonstrates that the absorption reduction at the low pumping intensity is mainly due to the interference between the two dressed states, not due to the ac–Stark-shift effect.

We propose a measurement scheme to determine the complete state of a single mode of the quantized electromagnetic field in a cavity.

We show that oscillations in photocount statistics will be destroyed by a sufficient admixture of thermal noise. In particular, we derive a ‘‘diffusion’’ equation evolving in temperature (rather than time) that describes the response of the photocount distribution to the admixture of such noise. We also derive an analytic condition for the temperature to guarantee the existence of these oscillations.