Related papers: Resonant light delay in GaN with ballistic and dif…
Light scattering in dense media is a fundamental problem of many-body physics, which is also relevant for the development of optical devices. In this work we investigate experimentally light propagation in a dense sample of randomly…
Femtosecond pump-probe (PP) differential reflectivity spectroscopy (DRS) and four-wave mixing (FWM) experiments were performed simultaneously to study the initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats between…
The study of short-term variability properties in AGN jets has the potential to shed light on their particle acceleration and emission mechanisms. We report results from a four-day coordinated multi-wavelength campaign on the highly-peaked…
We study the gravitational time delay in ray propagation due to rotating masses in the linear approximation of general relativity. Simple expressions are given for the gravitomagnetic time delay that occurs when rays of radiation cross a…
During reionization, a fraction of galactic Ly$\alpha$ emission is scattered in the intergalactic medium (IGM) and appears as a diffuse light extending megaparsecs from the source. We investigate how to probe the properties of the early…
Variable continuum emission from AGN can be used to probe the structure of their accretion disks via reverberation mapping. Assuming a variable, hot inner light source irradiates the surrounding accretion disk, time delays between different…
Light propagation is viewed as a process involving mutual creation of electric and magnetic fields. This viewpoint is used to argue that the conventional retarded solutions to electromagnetic wave equations (whose source is a current…
We demonstrate experimentally that a cloud of cold atoms with a size comparable to the wavelength of light can induce large group delays on a laser pulse when the laser is tightly focused on it and is close to an atomic resonance. Delays as…
A quantitative theory of spectral lags for $\gamma$-ray bursts (GRBs) is given. The underlying hypothesis is that GRB subpulses are photons that are scattered into our line of sight by local concentrations of baryons that are accelerated by…
The estimation of light velocity dispertion caused by quantum fluctuations influence on electromagnetic wave propogation in four-dimensional space-time is presented. Analytical cosmological solutions for the flat and open Universe for the…
High-resolution soft X-ray emission and absorption spectra near the N K-edge of wurtzite GaN are presented. The experimental data are interpreted in terms of band structure based full-potential electronic structure calculations. The…
The propagation length of high-energy photons through the Universe is limited by $e^+e^-$ pair production on the extragalactic background radiation. Previous studies reported discrepancies between predicted and observed attenuation,…
Photons of energy larger than 100 MeV from long-GRBs arrive a few seconds after <10 MeV photons do. We show that this delay is a natural consequence of a magnetic dominated relativistic jet. The much slower acceleration of a magnetic jet…
Radio signals are delayed when propagating through plasma. This type of delay is frequency-dependent and is usually used for estimating the projected number density of electrons along the line of sight, called the dispersion measure. The…
Gamma ray bursts (GRB's) often feature subpulses that have a distinctively asymmetric profile -- they rise quickly and decay much more slowly, while their spectrum softens slightly with observer time. It is suggested that these subpulses…
Thanks to the availability of high-resolution high-sensitivity telescopes such as the Very Large Array, the Hubble Space Telescope, and the Chandra X-ray Observatory, there is now a wealth of observational data on relativistic jets from…
We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous (>10^{42} erg/s) partly extended (> 30 kpc diameter) X-ray emission from the double-nucleus ultraluminous infrared galaxy NGC 6240. The ROSAT…
The shape of an RF pulse is distorted upon propagating through an X-band accelerator structure due to dispersive effects. This distortion together with beam loading introduce energy spread between 192 bunches. In order to minimize this…
Relativistic jets of radio loud active galactic nuclei (AGN) produce highly directed, intense beams of radiation. A fraction of this beamed radiation scatters on the thermal plasma generally surrounding an AGN. The morphology of the…
Although soft X-ray absorption features in AGN were discovered almost ten years ago, the nature and location of the gas creating them has remained controversial. However, by making use of the newly-available high-resolution spectra provided…