Krassimir Krastev

SAFRAN A.S. group · EU projects

The goal of the MONA project (Merging Optics and Nanotechnologies) is to leverage synergies in photonics and nanotechnologies, seeking to increase the impact and efficiency of investment in European research. There are three principal objectives for the MONA project: · Create a common site for the exchange of information concerning research, networ...

In this paper we present measurements of crosstalk between two adjacent channels in a fiber parametric amplifier based on the use of a high nonlinear dispersion shifted fiber. For an input signal power of -17 dBm and in the case of high gain regime (> 20 dB) the crosstalk induced power can reach -5 dBm.

The damage induced to various multilayer interferential mirrors (MIMs) by intense soft X-ray plasma-laser sources are studied both experimentally and theoretically. The mirrors consist of periodic bilayers made up with C/W, Si/Mo, Si/W\. One set of Si/W MIMs is coated with a 100 nm Si film devised to protect the multilayer structure. In the experim...

We propose a method to reduce the bandpass of soft x-ray multilayer Bragg reflectors. It consists in etching down to the substrate a multilayer mirror having a large number of bilayers in order to get a lamellar grating with a multilayer bar width representing only 10%–30% of the grating period. The grating is used at the zeroth diffraction order....

In this article, we consider the diffraction of an electromagnetic wave by a lamellar amplitude multilayer grating (LAMG), in conical mountings, when the incident wave vector is not in a plane perpendicular to the grooves. A modal expansion technique based on Bloch's theorem is used with an R-recursive propagation scheme. We compare the zeroth orde...

We apply a recursive propagation method to the modal theory of diffraction by laminar amplitude multilayer gratings (LAMG’s). We compute the reflection efficiency in the X-UV domain of several LAMG’s and show the numerical stability of this method with respect to a nonrecursive one.

A Lamellar Multilayer Amplitude Grating (LMAG) etched in a multilayer mirror was designed for an efficient use in the 1 keV region, through a multistep process involving sputtering coating, electron lithography and reactive ion etching. The multilayer structure has 115 bilayers of 3.1 nm thickness, and the grating of period 1.33 μm has a small line...

We present the results of recent experiments concerning the interaction of high intensity-short laser pulses with dielectric materials. The laser pulse creates a high density of free carriers, and two complementary experiments have been carried out to investigate the relaxation mechanisms in the solid, during and just after the excitation pulse. Th...

We report the first space-time observation of the ultrafast excitation and relaxation of an electron gas pumped into the conduction band of a wide band-gap insulator by an intense subpicosecond laser pulse. The experiment is based on a new phase-sensitive technique which allows a resolution of 120 fs in time and 5 $\mu${}m in space. In crystalline...

We measure the kinetic energy of photoelectrons emitted from an alpha-quartz surface irradiated by short (100 fs) and intense laser pulses. In the high intensity regime (above 100 GW/cm2), we observe a high-energy tail in the photoemission spectra at 620 and 560 nm. This effect disappears for the doubled frequencies. These observations give direct...

When an ultra-short and intense laser field propagates inside a dielectric medium, it induces a strong polarization field and, if the intensity is high enough, it produces a high density of electrons and holes. In this paper, we report on an experiment based on a new phase-sensitive technique [1,2] which allows the direct visualization of the polar...

We find conditions for collimation and guiding of two light beams in a nonlinear bulk medium. The spatial parameters of each beam of the symbiotically coupled pair depend critically on the cross-phase modulation from the complementary beam. The diffraction divergence and self-phase modulation can be offset by proper choice of the wavelength, the va...