Finite Linewidth Research Articles

Hole-density evolution of the one-particle spectral function in doped ladders

The spectral function $A({\bf q}, \omega)$ of doped $t-J$ ladders is presented on clusters with up to $2 \times 20$ sites at zero temperature applying a recently developed technique that uses up to $\sim 6 \times 10^6$ rung-basis states. Similarities with photoemission results for the 2D cuprates are observed, such as the existence of a gap at $(\pi,0)$ near half-filling (caused by hole pair formation) and flat bands in its vicinity. These features should be observable in ARPES experiments on ladders. The main result of the paper is the nontrivial evolution of the spectral function from a narrow band at $x=0$, to a quasi-noninteracting band at $x \geq 0.5$. It was also observed that the low-energy peaks of a cluster spectra acquire finite line-widths as their energies move away from the chemical potential.

SNOM-induced photoluminescence of individual InGaAs quantum dots using etched metal-coated fibre tips

Scanning near-field optical microscopy is used to investigate the photoluminescence of individual In0.4Ga 0.6As quantum dots. The high transmission efficiency of etched fibre tips allows investigations of quantum dots at room temperature with sufficient intensity, even after coating the tip with metal for background elimination. The pure background-free signal of single quantum dots results in Lorentzian photoluminescence spectra with finite line widths of 10–20 meV at room temperature to <1 meV at 4 K. This is in contrast to the expectation of extremely narrow lines in the microelectron-volt region. Copyright © 1999 John Wiley & Sons, Ltd.

Coherent Optical Heterodyne PSK Receiver Performance in Multichannel Environment

This paper presents the analysis of coherent optical heterodyne phase-shift keying (PSK) receiver performances in the presence of the laser phase noise, photodiode shot noise and adjacent channel interference. The reference carrier is extracted by the nonlinear phase locked loop (PLL). Due to the finite laser linewidth, both the useful signal phase and adjacent channel interference phase have the Gaussian distribution. Taking the previously mentioned influences into consideration, the steady state phase error probability density function (PDF) is determined as well as the average error probability (P c ) dependence on signal to noise ratio (SNR).

The vibrational spectrum of amorphous materials obtained by the use of an Anderson-like Hamiltonian

Abstract An analytical model, based on an Anderson-like Hamiltonian, is developed in order to describe the vibrational spectrum of amorphous materials. A numerical analysis of the model, performed for the simplest case of a single acoustic-like band, shows the basie features of the vibrational spectrum typical of disordered materials, e.g. the boson peak and a finite line-width of the low-frequency excitations.

Photon correlation spectroscopy on flowing polydisperse fluid-particle systems: theory

We develop an analytical expression for the homodyne autocorrelation function of laser light scattered by a laminar flow of a polydisperse particle-fluid system. In contrast to the already existing literature on the development of autocorrelation functions, we explicitly begin with the effects of the finite linewidth of the light source, the spatial and temporal intensity averaging that is due to the detection process, the Brownian particle movement on the amplitudes of the scattered light waves as well as on the degree of resolution that we introduce in this paper, and a general system velocity v = (v(x), v(y), v(z)). One main result is a new physical interpretation of the well-known, generally empirically introduced coherence factor. Quantities that are comparable to the well-known degree of coherence, coherence area, and number of coherence areas have also been obtained. Finally the investigations are simplified to an autocorrelation function that can be used for the analysis of fluid-particle systems in the low Knudsen number regime. It is shown that in this case particle size or size distribution, system velocity, and particle concentration can be obtained simultaneously. The developed autocorrelation function is related to frequently analyzed special cases and compared with expressions from the literature.

Third-harmonic generation via laser-plasma interaction: Beyond the low-density approximation

We study the third harmonic generation via laser interaction with a cold homogeneous plasma, in the one-dimensional approximation. We consider moderate values of the electron plasma density such that the pump laser pulse propagates inside the plasma without changing its shape. Our laser model allows for a finite spectral linewidth, which leads to a damping of the oscillatory behaviour of the third-harmonic power conversion rate as a function of the normalized plasma density, even for very low densities.

Tunable diode laser spectrometer apparatus function

Lead-salt diode lasers (TDL) are extensively used in experiments involving absorption line intensity and absorption linewidth measurements. In these experiments, the finite TDL linewidth poses a problem and it is necessary to know precisely the TDL lineshapes and linewidths. For this purpose, three methods are used: records of spectra at low pressure, etalon fringes analysis and heterodyne measurements.

Advanced Knowledge for Impurity Motion of Oxygen in Silicon and its Application to Defect-State Analysis

AbstractWe review our two models for the impurity excitation of the oxygen in silicon. The first model aims to explain the energies and intensities of the infrared absorption lines. The coupled excitation is formulated for the first time under the D3d symmetry. Taking into account the lowenergy excitation of the oxygen, the A2u local mode, and the anharmonic coupling between them, we quantitatively describe the absorption lines in the 30-, 1100-, and 1200-cm−1 bands, including those of the 18O isotope. We next take into account the A1g local mode, the Eu resonant mode, and the couplings between the excitation elements. This enables us to qualitatively explain the origin and characteristic aspects of other absorptions, e.g., the 500- and 1700-cm−1 bands. The second model is a simplification of the first one with the coupling to the band (extended) phonons included. The model describes the strong temperature dependence of the line widths observed for both of the phonon-resonant 30-cm−1 band and the phonon-off-resonant 1100-cm−1 band. The life-time limiting process causing the finite line-widths is shown to be the one-phonon transitions in the energy-level ladders of the low-energy excitation each belonging to the ground and the first excited states of the A2u local mode. The vibrational excitations of the similar impurity systems in Si, Ge, Ge xSi1−x crystals are analyzed.

Quantum interference in resonance fluorescence for a driven V atom

We investigate the effect of quantum interference between the two transition pathways from the excited doublet to the ground level of a driven V atom on the spectral features of the resonance fluorescence emission. The ultranarrow spectral line at line center, which arises due to quantum interference, occurs over a wide range of parameters. The smaller the ratio of the excited doublet splitting to the effective Rabi frequency, the more pronounced the spectral line narrowing. However, the fluorescence emission is completely quenched when the atomic dipole moments are exactly parallel and the driving field is tuned to the average frequency of the atomic transitions. The narrow line is due to the slow decay rate of one dressed state, while the quenching arises from dressed-state trapping. A finite laser linewidth destroys the spectral narrowing features and the fluorescence quenching.

Electromigration mechanisms in conductor lines: Void shape changes and slit-like failure

Abstract A detailed analysis of electromigration damage in unpassivated Al-based conductor lines was conducted. Damage observations revealed that slit-like voids in lines having a bamboo structure develop from equi-axed voids through a shape change driven by the “electron wind”. In order to simulate this behavior a numerical model was developed in which electromigration-driven diffusion on the void surfaces is assumed to act as the primary transport mechanism. This theoretical treatment considers the influence of the current density distribution and the temperature field in the vicinity of the void, while at the same time taking account of the finite line width as well as surface tension effects. In addition, the often observed facetting of voids is discussed on the basis of simulations in which anisotropic surface diffusivity was assumed. It will be shown that void shape changes and slit formation have a major influence on the performance of lines with bamboo structure and that the modeling has the potential of predicting their life times.

Radiation linewidth of a long Josephson junction in the flux-flow regime.

A theoretical model for the radiation linewidth in a multifluxon state of a long Josephson junction is presented. Starting from a perturbed sine-Gordon model with a temperature-dependent noise term, we develop a collective coordinate approach which allows us to calculate the finite radiation linewidth due to excitation of the internal degrees of freedom in the moving fluxon chain. At low fluxon density, the radiation linewidth is expected to be substantially larger than that of a lumped Josephson oscillator. With increasing the fluxon density, a crossover to a much smaller linewidth corresponding to the lumped oscillator limit is predicted. \textcopyright{} 1996 The American Physical Society.

Influence of driving-field phase fluctuation on absorption and dispersion in a simple three-level atomic system

The steady-state behavior of a simple three-level atomic system has been investigated by taking into account the effect of phase fluctuations in the driving field. For a monochromatic driving field, lasing with or without inversion can be established over a wide frequency range for the probe and driving fields. A large refractive index can also be generated even if the population inversion is positive. For a finite linewidth of the driving field, the refractive index enhancement tends to decrease. Furthermore, a behavior change from inversion laser to noninversion laser can occur as the driving field linewidth increases.

BER impairment due to laser linewidth in OFDM-OOK systems using double-cavity Fabry-Perot demultiplexers

We report on the impact of finite laser linewidth on the bit error rate (BER) performance in directly detected optical frequency-division multiple-access (OFDMA) employing double-cavity Fabry-Perot (FP) filters. Three different double-cavity FP demultiplexers have been considered in this study. Also the laser linewidth impairment on the crosstalk probability mass functions, the crosstalk power penalties and the OFDMA network capacity are calculated. The results demonstrate that, even though these demultiplexing schemes are much superior than single-cavity FP filters for highly coherent sources (laser linewidth lower than a few megahertz), when laser linewidth increases this feature appears to be much less significant due to the severe impairment of the laser linewidth on the BER performance, specially for structures with higher optical filter finesse.

Radiation linewidth of a long Josephson junction in the flux-flow regime

Theoretical model for the radiation linewidth in a multi-fluxon state of a long Josephson junction is presented. Starting from the perturbed sine-Gordon model with the temperature dependent noise term, we develop a collective coordinate approach which allows to calculate the finite radiation linewidth due to excitation of the internal degrees of freedom in the moving fluxon chain. At low fluxon density, the radiation linewidth is expected to be substantially larger than that of a lumped Josephson oscillator. With increasing the fluxon density, a crossover to a much smaller linewidth corresponding to the lumped oscillator limit is predicted.

Impact of the extinction ratio on the BER performance in directly detected OFDM systems

The crosstalk induced by considering a non-ideal extinction ratio and its influence on the BER performance in directly detected OFDM are studied in this letter. Also, the finite laser linewidth impairment is considered in the results, and a comparison of both degrading mechanisms is carried out. The results show that a significant reduction of the network capacity may be obtained due to the extra crosstalk level produced by lower extinction ratios in on-off keying (OOK) modulated optical transmissions, even when highly coherent lasers are used.

Role of pump phase fluctuations in a two-photon phase-sensitive amplifier.

We consider a phase-sensitive amplifier that consists of a system of three-level atoms in a cascade configuration that is prepared in a coherent superposition of upper and lower states by a strong classical field. We have studied the role of pump phase fluctuations associated with the finite linewidth on the quantum-statistical properties of the radiation field. A study of the output field characteristics reveals that the presence of a very weak pump field gives rise to equal variances in both field quadratures which are independent of linewidth. On the other hand, the presence of a strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations.

The Effect of Phase Fluctuation on Electromagnetically Induced Transparency, Inversionless Lasing and Refractive Index Enhancement in a Λ System

Abstract The steady-state behaviour for a Λ-type, three-level atomic system has been analysed by taking into account the effect of the phase fluctuation. It is shown that, for a monochromatic driving field, even if the probe field is in resonance with the corresponding atomic transition, a large refraction index can still be generated; for a finite linewidth of the driving field, inversionless lasing and index enhancement tends to disappear. Furthermore, the linewidth prevents the transparency of the medium.

Off-Resonance Effects in Two-Dimensional Zero-Field Nutation NQR Spectroscopy

Abstract Two-dimensional zero-field nutation NQR spectroscopy enables one to determine the quadrupole coupling constant and the asymmetry parameter in a single experiment on powder samples. The method has been originally developed for the conditions which apply to narrow-line solids so that the nutation frequency is much larger than the NQR linewidth. The irradiation must also be on-resonance. In broad-line solids, these conditions are not fulfilled, and consequently the nutation frequency changes over the NQR lineshape with the irradiation offset. The nutation lineshape varies with offset over the NQR spectrum in a complicated way. The rather simple nutation lineshapes, which can be used for the asymmetry parameter η determination, are obtained only in the on-resonance irradiated parts of the NQR spectrum. Even there, the presence of a finite homogeneous linewidth smears and obscures the characteristic nutation lineshapes, which for narrow homogeneous linewidths exhibit singularities and shoulders. In this paper the theoretical description of the off-resonance effects in the 2D nutation NQR spectroscopy is given and the results are compared to the experiment for a broad-line proton glass Rb 0.98 (NH 4 ) 0.02 H 2 AsO 4 at T = 77 K.

The effect of phase fluctuation on absorption and dispersion in a ∨ medium

Abstract The effect of phase fluctuation on absorption and dispersion in a ∨-type, three-level atomic system has been analyzed. It is shown that the refractive index enhancement tends to decrease for driving fields of finite linewidth. Furthermore, for the case of zero incoherent pumpings, the transparency of the medium occurring for zero detunings is destroyed when the linewidth is not zero.

Impact of finite laser linewidth on the performance of OFDM networks employing single-cavity Fabry-Perot demultiplexers

In this paper we investigate the impact of finite laser linewidths (i.e. source partial coherence) on the crosstalk performance of optical frequency division multiplexing (OFDM) networks employing single-cavity Fabry-Perot demultiplexers. Results are presented that show the important limitation imposed by the finite laser linewidths on the attainable bit error rate (BER), maximum number of users, and the required power penalties to overcome this impairment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>