Scintillation

About: Scintillation is a research topic. Over the lifetime, 14022 publications have been published within this topic receiving 187694 citations.

Scintillations of incoherent flat-topped Gaussian source field in turbulence

Abstract: The intensity fluctuations of incoherent flat-topped Gaussian beams are evaluated when such sources are used in weakly turbulent horizontal atmospheric links. The formulation is developed for a detector having a response time much longer than the source coherence time. The flat-topped Gaussian profile is obtained by superposing many Gaussian beams, then the incoherence is introduced through delta correlation in space. The scintillation index of the incoherent flat-topped Gaussian beams is found to be smaller than the scintillation index of the corresponding incoherent Gaussian beams at the same link length, source size, and wavelength. When compared with the coherent counterparts, the intensity fluctuations of the incoherent flat-topped Gaussian beams are much smaller, yielding the same value only at the spherical wave limit, as expected. Transmitter aperture averaging is a special case of our solution.

Computer simulation of the light yield nonlinearity of inorganic scintillators

Abstract: To probe the nature of the physical processes responsible for the nonlinear scintillation light yield of inorganic scintillators, we have combined an ab initio based Monte Carlo code for calculating the microscopic spatial distributions of electron-hole pairs with an atomistic kinetic Monte Carlo (KMC) model of energy-transfer processes In the present study, we focus on evaluating the contribution of an annihilation mechanism between self-trapped excitons (STE) to the scintillation response of pure CsI and Ce-doped LaBr3 A KMC model of scintillation mechanisms in pure CsI was developed previously and we introduce in this publication a similar model for Ce-doped LaBr3 We show that the KMC scintillation model is able to reproduce both the kinetics and efficiency of the scintillation process in Ce-doped LaBr3 Relative light output curves were generated at several temperatures for both scintillators from simulations carried out at incident γ-ray energies of 2, 5, 10, 20, 100, and 400 keV These simulation

Long-Term Scintillation Studies of Pulsars. II. Refractive Effects and the Spectrum of Plasma Density Fluctuations

Abstract: Refractive scintillation effects in pulsars are powerful techniques for discriminating between different models proposed for the electron density fluctuation spectrum in the interstellar medium. Data from our long-term scintillation study of 18 pulsars in the dispersion measure range 3-35 pc cm-3 (Paper I) are used to investigate two important observable effects of refractive scintillation, viz., (1) modulations of diffractive scintillation observables and flux density, and (2) drifting bands in dynamic scintillation spectra. Our data provide simultaneous measurements of decorrelation bandwidth, scintillation timescale, flux density, and drift rate of patterns. The observed modulations of the first three are compared with the available theoretical predictions, and constraints are placed on the power spectrum of plasma density fluctuations. The measured modulation indices are found to be larger than predicted by a Kolmogorov form of density spectrum. The properties of the drift rate of patterns along with the diffractive scintillation parameters have been used to estimate independently the slope of the density power spectrum, which is found to be consistent with a Kolmogorov form for several pulsars. The contradictory results from these two independent methods of constraining the electron density spectrum are not reconcilable with the simple theoretical models based on power-law forms of density spectrum. Our observations show anomalous scintillation behavior such as persistent drifting bands for some pulsars. This can be interpreted as an excess power in the low wavenumber range (~10-12 to 10-13 m-1) compared to the Kolmogorov expectations, or the existence of localized density structures. The results from our observations are discussed in combination with those from earlier studies in an attempt to understand the overall nature of the density spectrum. The emerging picture is a Kolmogorov-like spectrum (α≈11/3) in the wavenumber range ~10-6 m-1 to ~10-11 m-1, which either steepens or has a bump near ~10-12 to 10-13 m-1. The accumulated data also suggest the existence of discrete density structures along some lines of sight. We also discuss the possible implications of our results for the theoretical models.

A global ionosphere scintillation propagation model for equatorial regions

Abstract: The formulation of a wave propagation model through a turbulent ionosphere is presented. The calculation of the transmitted field enables the estimation of signal impairments, especially its intensity and phase fluctuations. The model outputs are compared with measurement results. This was performed for the intensity and phase fluctuation levels and for the spectral content of the transmitted signal. The field second-order moment calculation is then presented. The mutual coherence function characterizes the channel transfer function. It is required for radar performances assessment after propagation through the turbulent medium. It was demonstrated that under simplified hypothesis, an analytical solution can be derived allowing a sensitivity analysis study.

Comparison between in‐situ spectral measurements of F‐region irregularities and backscatter observations at 3 m wavelength

Abstract: In situ measurements of equatorial electron density irregularities in the F-region by rockets and satellites have yielded a power-law form of one-dimensional wave number spectrum of spectral index 2 in a direction transverse to the magnetic field over a scale size range of several km to several tens of m. Equatorial scintillation measurements in the WHF/UHF band which are most sensitive to irregularities of several km to several hundred m are consistent with the in situ spectral results. The backscatter measurements made at Jicamarca at 50 MHz provide an additional measurement of the spectral power at 3m wavelength. Computations are presented for the backscatter intensity expected from irregularities with power law spectrum in the transverse direction but which are infinitely elongated along the magnetic field. The computed intensity is compared with actual backscatter measurements and correlated scintillation observations. It is found that in order to reconcile the backscatter measurements with the simultaneous VHF/UHF scintillation observations a gaussian type cut-off of the power-law spectrum is necessary at m wavelengths near the O+ ion gyro-radius.