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Pursuant to a Congressional act in 2008, the Department of Health and Human Services established the Interagency Breast Cancer and Environmental Research Coordinating Committee to address the burden of breast cancer in the United States. Subsequently, the Committee recommended researchers study the timing of exposure to breast cancer risk factors. Given the high breast cancer mortality rate on Staten Island, this paper presents a case-control study investigating breast cancer risk associated with puberty while living on Staten Island. The dataset combined New York City Department of Health and Mental Hygiene female death certificate information between 1985 and 2006, with life history information from newspaper obituaries. Data analyzed included: age, length of residence on Staten Island, birth on Staten Island, and residence on Staten Island during puberty. Cases were individuals who died of breast cancer and controls were individuals who died of non-malignant causes. Analysis included multivariate logistic regression on the full dataset and multiple replicates of randomized one case to two controls simulations. Results indicated that living on Staten Island during puberty (ages 9–19) was associated with an elevated risk of dying from breast cancer (odds ratio 1.35, p < 0.001, 95% CI = 1.18, 1.55). This paper suggests the importance of studying puberty as a window of susceptibility for breast cancer risk.

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.

A temperature sensor based on an array of carbon nanowires written by a 30 keV Ga+ focused ion beam on diamond substrate has been developed. The temperature sensitivity of the electrical conductuctance between the nanowires is explained by the thermal activation of charge carriers in a heterostructure graphite-diamond over an energy barrier of 0.24 eV. The sensor shows an exponential increase of current with temperature at a rate of 0.1 dB/°C in the temperature range from 40 to 140 °C. The advantages of the novel carbon nanowire sensor are light blindness, compatibility with carbon nanotechnology, reproducibility and simplicity of fabrication. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, we present a systematic study of photoluminescence (PL), photoluminescence excitation (PLE) and resonant photoluminescence on AlGaAs/GaAs selectively doped quantum well structures, in order to better understand the optical properties of these systems. To support the interpretation of our experimental results we have calculated the confined states for the systems in the effective mass approximation, taking into account many body effects, such as exchange and correlation in the local density approximation.

A general procedure for calculating luminescence spectra from $\ensuremath{\delta}$-doping structures of semiconductors is developed. The electron and hole states are self-consistently calculated within the eight-band Kane model. Explicit results are obtained for $p$-type $\ensuremath{\delta}$-doping wells and superlattices in GaAs. For a prototype superlattice (SL) it is demonstrated how the luminescence spectra of $\ensuremath{\delta}$-doping structures depend on their self-consistent potentials, band structures, and oscillator strengths of radiative recombination processes between extended electron and confined hole states. Wave-vector conserving (direct) and nonconserving (indirect) transitions are considered. Luminescence spectra are calculated for a series of $p$-type $\ensuremath{\delta}$-doping SL's, varying their sheet doping concentrations, doping spreads, and periods. A comparison with experimental spectra shows that direct transitions may be ruled out. The indirect spectra are dominated by an emission band below the gap whose structures reflect the various occupied hole subbands. Increasing the temperature, the calculated hole emission bands become stronger, in contrast with experiment. This discrepancy is solved by means of a photoinduced electron confinement.

Experimental and theoretical studies on n -type multiple δ-doped GaAs layers are reported. Photoluminescence is measured and compared with results of self-consistent electronic-structure calculations. A series of samples with different donor concentrations in the δ-doped layer and a fixed distance between adjacent Si-doped layers (ds = 300 A) were analysed. The PL spectra of the investigated samples do not show transitions involving confined electronic minibands. However, the full width at half maximum of the observed main emission band may be correlated with the calculated electronic miniband structures.

We derive an engineering methodology and study the impact of polarization-dependent gain (PDG) on the design of cascaded semiconductor optical amplifier (SOA)-based coarse wavelength-division-multiplexing systems. System specifications can be determined based on receiver optical signal-to-noise ratio (OSNR) requirements and cascaded-SOA OSNR penalty calculations that include a simplified model to calculate PDG statistics

Quantum evolution of a collective mode of a Bose-Einstein condensate containing a finite number N of particles shows the phenomena of collapses and revivals. The characteristic collapse time depends on the scattering length, the initial amplitude of the mode and N. The corresponding time values have been derived analytically under certain approximation and numerically for the parabolic atomic trap. The revival of the mode at time of several seconds, as a direct evidence of the effect, can occur, if the normal component is significantly suppressed. We also discuss alternative means to verify the proposed mechanism.

We have analyzed the behavior of a diode laser with low-amplitude optical injection. The noisy injection field has phase fluctuations only, with a linewidth larger than both the free-running slave laser linewidth and the locking range. Simulations show that the laser output spectrum can be much narrower than the injection spectrum and may have a dip at the free-running laser frequency. A model describing these features is based on linear superposition of the stationary responses to monochromatic injection. The mechanism of line narrowing is that the response to injection outside the locking range lies mainly inside.

We report the first experimental observation of irregular picosecond light pulses within the coherence collapse of a semiconductor laser subject to delayed moderate optical feedback. This pulsing behavior agrees with the recent explanation of low frequency fluctuations as chaotic itinerancy with a drift. Theory and experiments show very good agreement.

We have performed a systematic study of photoluminescence (PL) line shape in n-type σ-doped In 0.15 Ga 0.85 As/GaAs quantum wells (6 QWs). Samples grown by molecular beam epitaxy with well widths of 60, 100, 300 A, with sheet doping concentration ranging from 10 11 to 10 13 cm -2 , were analysed. Two positions were considered for the doping planes, at the centre (symmetric) and at the edge (asymmetric) of the QW. The luminescence spectrum from the symmetric 60 A δ QW exhibits a dominating broad structure that at low excitation condition and low temperature has an almost rectangular form. The square shape of this spectrum is explained by the collective recombination of electrons from the conduction band with thermalized photogenerated holes. For the symmetric L W = 300 A samples, the PL spectra display an almost symmetric peak followed by a small shoulder on the higher or lower energy side depending on the carrier concentrations. For the asymmetric 300 A δ QW sample two distinct peaks were observed. They were correlated to transitions involving the fundamental and first excited electronic subbands.

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. >

We investigate the problem of designing and engineering metropolitan area optical networks for the provisioning of multicast sessions. The Q-factor for each session is taken into account, aiming at maximizing the admitted number of connections.

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.

A new model describing laser noise in terms of non-Markovian stochastic phase jumps has been introduced by A.G. Kofman et al. (1988, 1990). An exact expression for the correlation function for the electric field is obtained. This expression, valid for all possible values of the parameters of the stochastic process, reduces to approximations reported by B.R. Mollow (1969). A procedure is described for the inverse problem of determining the stochastic parameters from measured data for real lasers. >

Strong laser fields, when tuned on resonance to an atomic (molecular) transition, give rise to the well-known triplet of resonance fluorescence. The laser field is normally assumed to be strong and monochromatic, even though the spectrum of real lasers is never a \ensuremath{\delta} function. A standard way to treat laser fluctuations has been to assume a well-defined nominal frequency and a randomly fluctuating phase. Recently we introduced the generalized jump model (GJM) for correlated phase fluctuations, where correlated phase jumps are considered, leading to Markovian as well as non-Markovian stochastic behavior. In the GJM, each phase jump may be correlated to the previous jump, and the degree of correlation, the typical jump size, and the mean time between jumps are the three parameters defining the stochastic character of the laser field. In this paper we apply the GJM model to the case of resonance fluorescence from an atom excited by a stochastic field. The ``standard'' Mollow triplet is obtained in the monochromatic limit of small jumps, and several new predictions are made in the different limits of the stochastic parameters. In the small-jump limit, a new ``field effect'' is predicted. The spectral line shape and the triplet separation deviate from the Mollow predictions for a monochromatic field in a substantial way, giving rise to observable differences.In the highly correlated small-jump limit, which is approximated by the Kubo oscillator model, the previous results are corrected to include nonzero line shifts and extended to the case of non-Lorentzian line shapes. In all regions, even input fields of the same line shape (which would be considered identical in the one-parameter linewidth description) give rise to very different output spectra, justifying the more complete stochastic description. Effective relaxation constants ${\mathrm{\ensuremath{\Gamma}}}_{1}^{\mathrm{*}}$ and ${\mathrm{\ensuremath{\Gamma}}}_{2}^{\mathrm{*}}$ that simplify the description of the spectrum are calculated in all appropriate cases, and ${\mathrm{\ensuremath{\Gamma}}}_{1}^{\mathrm{*}}$ is found to equal the input laser linewidth. In addition to predicting the resonance fluorescence spectra, the present analysis provides a way to extract the stochastic parameters from the nonlinear measurement in those cases where the linear characterization of the input field cannot do it. The analytic work is fully supported by extensive numerical simulations.

We investigate the OSNR performance of cascaded SOAs in CWDM metropolitan networks. SOA PDG and noise-figure requirements are determined by an engineering methodology based on careful receiver characterization. Performance is compared to conventional EDFA-amplified DWDM.

The transport properties of large-angle grain boundaries (GBs) containing point defects and charges in ${\text{YBa}}_{2}{\text{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) are studied by computer simulation methods. The results of simulation of the atomic structures of large-angle symmetrical tilt GBs $\ensuremath{\Sigma}5$ (misorientation angles $36.87\ifmmode^\circ\else\textdegree\fi{}$ and $53.13\ifmmode^\circ\else\textdegree\fi{}$), $\ensuremath{\Sigma}13$ (misorientation angles $22.62\ifmmode^\circ\else\textdegree\fi{}$ and $67.38\ifmmode^\circ\else\textdegree\fi{}$), $\ensuremath{\Sigma}17$ (misorientation angles $28.07\ifmmode^\circ\else\textdegree\fi{}$ and $61.93\ifmmode^\circ\else\textdegree\fi{}$), and $\ensuremath{\Sigma}29$ (misorientation angle $43.60\ifmmode^\circ\else\textdegree\fi{}$) containing point defects (neutral and charged oxygen and yttrium vacancies) are presented. The techniques of the strain analysis and the bond-valence-sum analysis are applied to determine the thicknesses of nonsuperconducting layers enveloping these GBs. Our data shows that the presence of neutral oxygen vacancies decreases the thicknesses of nonsuperconducting layers and may improve transport properties of some large-angle GBs. Adsorption capability of GBs with respect to neutral oxygen vacancies is evaluated. Its analysis demonstrates that the tilt GBs in YBCO are most probably intrinsically nonstoichiometric.

The effect of Bose-Einstein condensation, achieved recently for alkaline gases in magnetic traps, should lead to a strong enhancement of non-linear harmonic generation. A nearly resonant light imposed on the gas of two-level atoms excites the intra-atomic transitions and causes generation of various harmonics. Normally, in the thermal state of the gas, a contribution of the inter-atomic interaction to the non-linear harmonic generation is negligible. However, if a Bose-Einstein condensate (BEC) is present, the inter-particle interaction cannot be ignored. Considering second harmonic generation, we show that, in the presence of the BEC, the intensity of the second harmonic is proportional to (aN n)/sup 2/, where N and n are the total number and the effective density of the condensed atoms, respectively, and a stands for the scattering length describing the process of scattering of two excited atoms by each other so that, after the collision, one excited atom enters the condensate. We consider the interaction between light, represented by the electric field E, and the atomic Bose field /spl Psi/ as well as the two body interaction treated within the scattering length approximation.

The phenomenon of injection locking in a nearly resonant circuit is known since long. The last few decades considerable progress has been made in the field of optical resonators, of which a diode laser operating above threshold, and injected with monochromatic light from an independent source (in general a laser too) is an example. A lot of research has focused on the locking state (i.e. the laser exactly copies the input field) and its stability.1

Ten years ago it was reported that external optical feedback as weak as 1% can induce a semiconductor laser to suddenly lose its coherence: its linewidth changes from typically 100 MHz to more than 20 GHz. This phenomenon has been called Coherence Collapse and attracted a lot of research effort. By now most of the deterministic properties of Coherence Collapse are identified. In the routes to chaos the interplay between the relaxation oscillations and the delay-induced resonances of the external cavity is considered to be the key physical phenomenon.1

We show that, contrary to common wisdom, the maximum gain mode of semiconductor lasers subject to optical feedback is always stable. The minimum linewidth mode is shown to be subject to a Hopf bifurcation associated with destabilizing the relaxation oscillations. This explains the experimental observation of narrow-linewidth, single-mode diode lasers operating with high optical feedback. © 1995 The American Physical Society.

The Hopf bifurcation points for single mode solutions of the Lang and Kobayashi equations are determined using asymptotic methods. The approximation is based on a small parameter (epsilon) which is defined as the ratio of the photon and carrier lifetimes. The remaining parameters are scaled with respect to (epsilon) . The critical feedback rate for a Hopf bifurcation is studied in terms of the pump parameter and is either an 0((epsilon) ) or an 0((epsilon) 1/2) quantity. At a fixed value of the pump parameter, we obtain an expression of the Hopf bifurcation point in terms of the effective feedback strength and the feedback phase. In addition, we investigate the Hopf bifurcation point near and at the lasing threshold.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, the various physical mechanisms in low-frequency intensity fluctuations are identified, that occur when a diode laser is subject to moderate optical feedback while operating close to its solitary threshold. The maximum gain mode, which surprisingly often stable, serves as a seemingly unreachable goal for the system. In attempting to reach this mode, the system forms mode-locked pulses. In between pulses the mode-locking is frustrated and inevitably the system passes too close to one of the many saddle points, that will take the system back to the low power solitary laser state.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have analyzed the behavior of a diode laser with low-amplitude optical injection. The noisy injection field has phase fluctuations only, with a linewidth larger than both the solitary linewidth and the locking range. Simulations show that the laser output spectrum can be much narrower than the injection spectrum, and may have a dip at the solitary laser frequency. A model describing these features is based on linear superposition of the stationary responses to monochromatic injection. The mechanism of line narrowing is that the response to injection ouside the locking range lies mainly inside.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Induced-grating autocorrelation (IGA) is a simple technique that measures the electric field autocorrelation function. We examine the use of IGA in characterizing the properties of self- phase-modulated pulses in optical fibers. Excellent agreement is found between theory and experiment.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We show that, in nonlinear spectroscopy, the time‐domain response and frequency‐domain susceptibility are not related by an n‐dimensional Fourier transform. This result is a consequence of the noncommutativity of different‐time operators in semiclassical nonlinear‐optical perturbation theory.

An extension of the non-Markovian jump model of laser noise to the case of correlated frequency jumps is considered. The model parameters are the mean jump time the rms jump size and a correlation parameter which quantifies the degree of correlation between two successive jumps. A technique to obtain exact expressions for correlation functions is described. While the basic jump processes are stationary both the phase and frequency fluctuations are not. The field autocorrelation function for the pure phase jump process is stationary for all values of the correlation parameter. For the frequency jump process the average over all initial times of the two time field autocorrelation function is non zero only for fully anticorrelated jumps.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A non-Markovian model of correlated phase jumps is introduced for phase fluctuations of an electromagnetic field. This generalized jump model (GJM) treats phase jumps of arbitrary size, occurring at random times; but in contrast to previous work, the jumps are allowed to be fully correlated, partially correlated, or uncorrelated. The degree of correlation is defined by a single parameter derived from the theory. The familiar phase-diffusion model, telegraph-noise model, Burshtein model, and Brownian-motion-like model are all obtained from the GJM in the proper limits. The standard way of characterizing the spectrum of a laser has been the assignment of a single parameter---the linewidth. However, in experiments where the details of the fluctuations are important, or where exact line shapes are measured, this single-parameter characterization might be insufficient. This GJM describes most cases by a set of three stochastic parameters: the degree of correlation between the jumps, the characteristic jump size, and the mean time between jumps. In this paper expressions are derived for the correlation function and the spectrum of a stochastic field in terms of these three stochastic parameters. In addition to analytical work, detailed numerical simulations are presented for the various limiting cases of the model, and the agreement between theory and simulation is excellent. Since the stochastic parameters are not a priori known, a procedure is described for extracting the stochastic parameters from measurable quantities such as the field correlation function or spectrum. Since correlated fluctuations are very common in optics (any stabilization feedback procedure involves anticorrelation), the questions of relevance of the present model to problems of current interest in optical communication and nonlinear optics are also discussed.

In the study of the interaction of nearly resonant strong laser light with matter the laser light is often assumed to be monochromatic. In more detailed experiments, however, the material response manifests the stochastic nature of the exciting field, and a detailed description of the stochastic process is needed. The approach used by most workers1 has been to assume a constant amplitude, a fixed nominal frequency and a phase that fluctuates. The most common is the description of the phase diffusion or Brownian-motion like process. Other models that had been used are the phase telegraph noise model, where the field is assumed to have a constant amplitude, fixed frequency, and a phase that jumps at random times between two values, and the Burshtein model of phase jumps, where the phase is assumed to jump at random with a random size jump.

nized oscillations in the wings. These variations in the trace are the same as those that occur to the envelope of the high-frequency fringes in ISHGA traces, which are generally used to indicate the presence of the above two phase distortions. Conveniently, however, no highfrequency fringes occur in IGA methods. Other advantages of IGA methods include automatic phase-matching, single-wavelength operation, and applicability to most wavelength ranges (using a thermal grating simply requires an absorbing medium). We also show that a wide range of four-wave-mixing autocorrelation and IGA arrangements (that is, three-beam induced grating? two-beam coupling? phase conjugation, etc.) all yield identical theoretical results, specifically, the same two-dimensional integral of a fourth-order electric-field coherence function, which does not reduce to an intensity autocorrelation. In addition, we have performed numerical integrations, obtaining IGA and ISHGA traces for a variety of theoretical pulse distortions, including linear chirp, SPM, wave breaking, and phase and/or amplitude jitter. The table on the next page shows some of these traces. Note the close connection between IGA and ISHGA traces. ultrashort pulses

A single-mode laser subject to weak optical feedback may become a multistable system. When the hopping rate becomes appreciable, the output power spectrum will be modified by the hopping. By applying a novel spectral theory of frequency jumps on a two-mode external-cavity semiconductor laser, we give an explicit analytical expression for the power spectrum that consists of four contributions, two of which are a weighted sum of individual quasi-mode spectra and two of which express the additional spectral broadening that is due to the jumping process.

The effect of a low-frequency dissipative medium on the tunneling rate of a particle trapped in a metastable potential is investigated with the aid of a frozen-bath sudden approximation. The sudden theory is formulated for arbitrary time-dependent friction and for all temperatures at which the escape process is dominated by tunneling. The validity criterion of the theory is only that the bath frequency spectrum be substantially lower than the system frequency. It is applicable both in the weak- and strong-damping limits. The sudden theory is applied to tunneling in a cubic potential and a piecewise harmonic potential where the barrier frequency differs from the well frequency. In contrast to the ImF method, the sudden theory, when valid, can provide estimates of tunneling rates from well-defined excited resonance states and is not limited to estimates of only thermal rates. We find that, if the barrier is thin relative to the well, dissipation can serve to enhance tunneling rates from excited states.

The solution for the relevant Heisenberg operators of a quadratic time‐dependent quantum mechanical Hamiltonian is presented in convolution form suitable for the inclusion of thermal fluctuations. The approach to equilibrium of an oscillator in contact with a thermal bath is studied. An expression is obtained for the reduction of the random fluctuation width of the position coordinate as a consequence of the non‐Markovian nature of a quantized thermal bath.

The solution is obtained to the quantum mechanical linearly damped harmonic oscillator subjected to a time dependent driving force. This solution allows the calculation of interesting quantum quantities such as the Green’s function and the transition amplitudes between harmonic oscillator states. The specific results for a harmonic driving force are given.

The solution to the linear Heisenberg equations which result from the most general quadratic time dependent Hamiltonian is developed. The Green’s function is obtained, and the transition amplitudes between harmonic states are calculated.

A new non Markovian, correlated jump model for phase fluctuations of an electromagnetic field is introduced'. The phase diffusion, generalized telegraph, Burshtein and Brownian-motion-like models are all obtained from this model in the proper limits. The spectrum and correlation functions of the stochastic field are predicted, and detailed lineshapes of the Mollow triplet of resonance fluorescence are given and shown to depend on the field intensity, a purely non Markovian effect. Two different experimental procedures are proposed for the determination of the stochastic parameters of a laser field.

An expansion technique for the dipole interaction of a spin-J system with a quantized monochromatic electromagnetic field is developed. The energy levels are equally spaced and the rotating-wave approximation is used. Particular results of the application of the method are presented.

A formalism for a time-dependent harmonic oscillator is presented. The quantum-mechanical solution is developed and the Green's function is derived. Particular examples of runaway and dissipative behavior are considered.