Search results for "waves"
showing 10 items of 1766 documents
Shift-variant digital holographic microscopy: inaccuracies in quantitative phase imaging
2013
Inaccuracies introduced in quantitative phase digital holographic microscopy by the use of nontelecentric imaging systems are analyzed. Computer modeling of the experimental result shows that even negligible errors in the radius and center of curvature of the numerical compensation needed to get rid of the remaining quadratic phase factor introduce errors in the phase measurements; these errors depend on the position of the object in the field-of-view. However, when a telecentric imaging system is utilized for the recording of the holograms, the numerical modeling and experimental results show the shift-invariant behavior of the quantitative-phase digital holographic microscope.
The optical counterpart to SAX J1808.4-3658 in quiescence: Evidence of an active radio pulsar?
2003
The optical counterpart of the binary millisecond X-ray pulsar SAX J1808.4-3658 during quiescence was detected at V = 21.5 mag by Homer et al. (2001). This star shows a 6% semi-amplitude sinusoidal modulation of its flux at the orbital period of the system. It was proposed that the modulation arises from X-ray irradiation of the intrinsically faint companion by a remnant accretion disk, and that the bulk of the optical emission arises from viscous dissipation in the disk. The serious difficulty in this scenario lies in the estimate of the irradiating luminosity required to match the observational data, that is a factor 10-50 higher than the quiescent X-ray luminosity of this source. To over…
A model to interpret pulse phase shifts in AMXPs: SAX J1808.4-3658 as a proof of concept
2011
Abstract: Observational evidences of erratic 1(st) harmonic pulse phase shifts in accreting millisecond X-ray pulsars pulse phase evolution was reported by several authors. This effect always go together with much more stable 2(nd) harmonics pulse phase delays. Different possible explanations of these phase shifts have been given in literature. But all these interpretations do not explain why the 2(nd) harmonic are more stable than the 1(st) harmonic. The explanation of such a behaviour is of fundamental importance in order to gain an insight on the NS rotational behaviour and to remove the still present interpretative ambiguity on the results of timing analysis. We propose a simple toy-mod…
Observation of a unitary cusp in the thresholdγp→π0preaction
1997
A rigorous multipole analysis of the recent $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$ cross-section measurement is presented. The data were taken using the photon spectrometer TAPS at the tagged photon beam of the Mainz microtron. The $s$ and $p$ wave multipoles were extracted using minimal model assumptions. The predicted unitary cusp for the $s$-wave multipole ${E}_{0+}$ due to the two step $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}n\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$ reaction was observed. The results are consistent with one-loop chiral perturbation theory calculations for which three low-energy constants have been determi…
Vector description of higher-order modes in photonic crystal fibers
2000
We extensively study the propagation features of higher-order modes in a photonic crystal fiber (PCF). Our analysis is based on a full-vector modal technique specially adapted to accurately describe light propagation in PCF's. Unlike conventional fibers, PCF's exhibit a somewhat unusual mechanism for the generation of higher-order modes. Accordingly, PCF's are characterized by the constancy of the number of modes below a wavelength threshold. An explicit verification of this property is given through a complete analysis of the dispersion relations of higher-order modes in terms of the structural parameters of this kind of fiber. The transverse irradiance distributions for some of these high…
Role of Polarization Mode Dispersion on Modulational Instability in Optical Fibers
2001
We introduce the theory of modulational instability (MI) of electromagnetic waves in fibers with random polarization mode dispersion. Applying a linear stability analysis and stochastic calculus, we show that the MI gain spectrum reads as the maximal eigenvalue of a constant effective matrix. In the limiting cases of small or large fluctuations, we give explicit expressions for the MI gain spectra. In the general configurations, we give the explicit form of the effective matrix and numerically compute the maximal eigenvalue. In the anomalous dispersion regime, polarization dispersion widens the unstable bandwidth. Depending on the type of variations of the birefringence parameters, polariza…
A mode coupling analysis of the central peak at order disorder phase transitions
1993
The influence of local and translation invariant memory effects on the critical dynamics of a model undergoing a continous structural phase transition from a disordered (T>Tc) to an ordered distorted phase (T>Tc) is studied by mode coupling theory above the critical temperatureTc. It is shown that besides the existence of critical slowing-down modes there also exists a central peak as a consequence of correlations of the critical modes, increasing with the critical exponent γ when approachingTc. The dependence of the central peak on the wavevector\(\vec q\), temperatureT and on the spatial dimensiond is investigated. Ford=3 a scenario withlocal long time memory correlations is compared with…
Multimode emission in inhomogeneously broadened ring lasers
2001
The threshold for multilongitudinal-mode emission in inhomogeneously broadened ring lasers is analytically investigated. In the homogeneous limit the multimode instability corresponds to the classical Risken–Nummedal–Graham–Haken instability. It is found that by increasing the inhomogeneous linewidth, the instability threshold is decreased and the growth of high-frequency side modes is favored. In the limit where the population-inversion decay rate γ‖ is much smaller than the polarization decay rate γ⊥ (class B lasers), analytical expressions for the instability threshold are found, which are then generalized to three-level lasers for a comparison with experimental results obtained with erb…
Lepton mass effects for beam-normal single-spin asymmetry in elastic muon-proton scattering
2019
We estimate the beam-normal single-spin asymmetry in elastic lepton-proton scattering without employing the ultrarelativistic approximation. Our calculation is relevant for analyses of muon scattering at energies of few hundred MeV and below -- when effects of the muon mass become essential. At such energies, the transverse polarization of the muon beam is expected to contribute significantly to the systematic uncertainty of precision measurements of elastic muon-proton scattering. We evaluate such systematics using an example of the MUSE experiment at PSI. The muon asymmetry is estimated at about 0.1\% in kinematics of MUSE and it is the largest for scattering into a backward hemisphere.
Track reconstruction for theMu3eexperiment based on a novel Multiple Scattering fit
2017
The Mu3e experiment is designed to search for the lepton flavor violating decay μ + → e + e + e − . The aim of the experiment is to reach a branching ratio sensitivity of 10−16 . In a first phase the experiment will be performed at an existing beam line at the Paul-Scherrer Institute (Switzerland) providing 108 muons per second, which will allow to reach a sensitivity of 2 · 10−15 . The muons with a momentum of about 28 MeV/c are stopped and decay at rest on a target. The decay products (positrons and electrons) with energies below 53MeV are measured by a tracking detector consisting of two double layers of 50 μm thin silicon pixel sensors. The high granularity of the pixel detector with a …