A. M. Levine

Sisyphus effect in semiconductor lasers with optical feedback

We identify the various physical mechanisms in low frequency fluctuations, which occur when a semiconductor laser is subject to moderate optical feedback while operating close to its solitary laser threshold. In attempting to reach the maximum gain mode, which often is stable, the system forms short mode-locked pulses. In between pulses mode-slipping can occur, generally in the direction of maximum gain. Inevitably, the trajectory passes too close to one of the many saddle points, which will take the system back to the solitary laser state. >

Hamiltonian theory for vibrational dephasing rates of small molecules in liquids

A technique is developed for solving the generalized Langevin equation (GLE) describing anharmonic oscillators in the weak coupling limit. The GLE is rewritten as a Hamiltonian with a nonlinear system coupled to an infinite bath of harmonic oscillators. A normal mode transformation followed by a perturbation technique is used to obtain the fluctuating system frequency. When the method is applied to a single oscillator with cubic anharmonicity, both the classical and quantal dephasing rates are shown to be equal to the well‐known result of Oxtoby. The technique is also applied to a system with more than one vibrational degree of freedom (linear triatomic molecules) to obtain the dephasing rates for the symmetric and antisymmetric normal modes. The effects of system anharmonicity on frequency shifts are investigated.

Chirp and self-phase modulation in induced-grating autocorrelation measurements of ultrashort pulses

We show that induced-grating/four-wave-mixing ultrashort-pulse autocorrelation techniques that use slowly responding media offer the same phase information as interferometric second-harmonic generation. We also show that autocorrelation traces from nearly all possible induced-grating/four-wave-mixing beam geometries provide this information, with all yielding the same theoretical result, an integral of a fourth-order electric-field coherence function. Such traces clearly reveal chirp and self-phase-modulation effects without high-frequency fringes. Experiments using a two-beam-coupling arrangement in photorefractive media illustrate these effects.

Multicast Routing Algorithms Based on

We use novel ldquolight-tree balancing techniquesrdquo to investigate the problem of provisioning multicast sessions in metropolitan all-optical networks. The Q-factor for every path of a derived light-tree is calculated taking into account several physical layer constraints in the network and using a Q-budgeting approach. Based on the above performance, tree balancing techniques are applied to maximize the number of multicast connections that can be admitted to the network.

Q

It has been observed that an electron current drawn to an electrode immersed in a magnetized plasma can excite oscillation near the ion cyclotron frequency. A theory is derived which predicts such oscillation due to a destabilizing influence of the sheath voltage drop at the electrode on the plasma column. Experimental evidence is presented which shows that the present theory is more compatible with observations than an earlier explanation in terms of resonantly drifting electrons.

-Factor Physical-Layer Constraints in Metro Networks

We consider induced-grating autocorrelation (IGA) in a slowly responding medium and study three possible geometries (two-beam coupling, three-beam induced grating, and self-diffraction) in two different limiting cases (single-pulse experiments and many-pulse accumulated-grating experiments). We find that in five of these six cases the IGA trace is given by the squared amplitude of the electric-field correlation function, thus yielding information about the spectrum of the pulse. Theoretical expressions for the IGA trace are derived for both linearly chirped and self-phase-modulated pulses. Experiments performed with self-phase-modulated pulses are in excellent agreement with the theory. In this case we show how the measured IGA trace can be used to determine both pulse duration and pulse bandwidth.

Excitation of Electrostatic Ion Cyclotron Oscillations

Utilizing the Green’s function for a time dependent harmonic oscillator, we calculate the corresponding transition amplitudes. Particular examples of damped and runaway oscillators are discussed.

Induced-grating autocorrelation of ultrashort pulses in a slowly responding medium

Through a controlled laboratory study, theoretical modeling was developed that accurately relates the reflectance of turbid water to the concentrations of suspended and dissolved materials; this modeling will be useful in quantitatively mapping pollutant concentrations in lakes and rivers through aerial photography. Laser light illuminated water containing both Teflon particles and black dye. Over a large range of concentrations of these scattering and absorbing materials, measured reflectance was successfully predicted by a multiple scattering analysis. (Single scatter analysis produced serious errors.) The theoretical development involved solving the radiative transport equation and accounted for correlated scattering from closely spaced particles.

Transition amplitudes for time‐dependent harmonic oscillators

Carbon nanowires written by focused ion beam on diamond surface are novel nanostructures with interesting electronic properties. In this communication, carbon nanowire structures working as temperature and chemical sensors are reported. The sensor structures were made as arrays of carbon nanowires written by a 30 keV focused ion beam on polycrystalline CVD diamond films. The electronic structure of a carbon nanowire array is discussed as multiple unipolar heterodiodes graphite-diamond-graphite (G-D-G). The energy barrier of the G-D-G diodes has been found of a value 0.25 eV. The structures exhibited changes in conductance when measured at different temperatures or when put in proximity of some volatile liquids. This temperature and chemical sensitivity is explained by the activation of the charge carrier flow over the G-D barrier caused by temperature or by the charge of the analyte molecules adsorbed on the surface of the structure. The temperature response of the sensors in the range from 40 to 140 is exponential at a rate of 0.11 . The chemical sensitivity has been found selective and particularly pronounced for water vapor. The advantages of the novel carbon nanowire sensors are their blindness to visible light, compatibility with carbon nanotechnology, simplicity and reproducibility of fabrication. The all-carbon nature of the sensors implies their applicability in medicine and biology.

Multiple Scattering of Laser Light from a Turbid Medium

The structure of a turbulent gas flow may be probed by analyzing scintillations of a laser beam which has traversed the turbulent medium. This technique is used to measure the spectrum of neutral gas turbulence in a pipe flow where the gas is nonuniformly heated and weakly ionized by an electrical discharge. First, the usual isotropic analysis relating the spectrum of light scintillations to the fluid turbulence is extended to include strong anisotropy as is appropriate in the present case. Second, the gas turbulence spectrum revealed by the scintillation, as well as by a hot film anemometer, is compared with the spectrum of plasma density fluctuations. It is found that the scale size of the neutral gas turbulence is larger than the scale size of the plasma density fluctuations by a factor of 2 for a case in which the plasma column is constricted to a considerably smaller diameter than the pipe. This indicates that whenever the plasma production process is constricted to dimensions smaller than the gas tu...