We report on an experimental study of supercontinuum generation in photonic crystal fibers with low-intensity femtosecond pulses, which provides evidence for a novel spectral broadening mechanism. The observed results agree our theoretical calculations carried out without making the slowly varying envelope approximation. Peculiarities measured spectra and their explanation demonstrate that reason white-light is fission higher-order solitons into redshifted fundamental blueshifted...

Reversible structural changes of a nanostructure were measured nondestructively with subpicometer spatial and subpicosecond temporal resolution via x-ray diffraction (XRD). The spatially periodic femtosecond excitation gallium arsenide/aluminum arsenide superlattice results in coherent lattice motions 3.5-picosecond period, which was directly monitored by pulses at 1-kilohertz repetition rate. Small (DeltaR/R = 0.01) weak Bragg reflexes (R 0.005) detected. phase amplitude the oscillatory XRD...

We demonstrate a novel technique for pulse compression of few-millijoule pulses with shorter than 10 fs duration. Our relies on spectral broadening in white-light filament generated noble gas. In this we observe self-compression 45 down to below 8 duration without the need any additional dispersion compensation. Using input 5 mJ, generate compressed up 3.8 mJ energy. Therefore method is much more efficient previously demonstrated schemes. The peak powers 100 GW at kilohertz repetition rate...

Pulses with durations below 4 fs have been generated using the method of ultrafast molecular phase modulation. A laser pulse shorter than vibrational or rotational period obtains spectral broadening during propagation along a hollow waveguide filled previously impulsively excited Raman active gases. The induced time dependent phase, frequency, and frequency chirp are controllable by changing delay between excitation probe within period.

We analyze pulse self-compression in femtosecond filaments, both experimentally and numerically. demonstrate the compression of $45\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ pulses down to a duration $7.4\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ at millijoule energies. This sixfold self-generated filament does not require any means for dispersion compensation is highly efficient. compare our results numerical simulations, providing complete propagation model that accounts full dispersion,...

We report the first analysis of polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system by femtosecond x-ray diffraction. Two Bragg reflections provide information on coupled two relevant phonon modes for ferroelectricity perovskites, tetragonal distortion soft mode. Optical excitation ${\mathrm{SrRuO}}_{3}$ metal layers generates giant stress ($>1\text{ }\text{ }\mathrm{GPa}$) compressing ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}$ up to 2%. The...

Abstract Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in femtochemistry toolkit. Such dynamics are now within reach with instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess ultrafast nonadiabatic vibronic processes a prototypical complex system—the excited benzene cation. We use few-femtosecond duration extreme ultraviolet visible/near-infrared laser pulses prepare probe...

We demonstrate a subpicosecond 1 kHz femtosecond x-ray source with well-accessible quasi-point size (10 microm diameter) providing Cu K(alpha) emission maximum flux of 6.8 x 10(10) photons/s for continuous operation 10 h. A new geometry that essentially facilitates the adjustment and diminishes temporal jitter between probe laser pump pulse is implemented time-resolved diffraction experiments.

Femtosecond laser pulses tailored with closed-loop, optimal control feedback were used to excite oscillations in C60 large amplitude by coherent heating of nuclear motion. A characteristic pulse sequence results significant enhancement C2 evaporation, a typical energy loss channel vibrationally hot C60. The separation between subsequent combination complementary two-color pump-probe data and time-dependent density functional theory calculations give direct information on the multielectron...

We develop theoretically and confirm both numerically experimentally a comprehensive analytical model which describes the propensity rules in emission of circularly polarized high harmonics by systems driven two-color counter-rotating fields, fundamental its second harmonic. identify three responsible for contrast between $3N+1$ $3N+2$ harmonic lines HHG spectra noble gas atoms. demonstrate how these depend on laser parameters they can be used experiment to shape polarization properties...

Saturation of near-infrared absorption in Mg2SiO4:Cr is observed, and the cross section at 1.08 μm estimated to be σa = (2.3 ± 0.3) × 10−18 cm2. Q switching passive mode locking a Nd:YAG laser have been realized with saturable absorber.

The complex mechanism of multiple interactions between solitary and dispersive waves at the advanced stage supercontinuum generation in photonic crystal fiber is studied experiment numerical simulations. Injection high power negatively chirped pulses near zero dispersion frequency results an effective soliton fission process with red shifted Raman solitons waves. These may result relative acceleration further collisions them quasi-elastic or quasi-plastic kinds. In spectral domain these...

Time-resolved extreme ultraviolet (XUV) transient absorption spectroscopy of iodomethane and iodobenzene photodissociation at the iodine pre-N4,5 edge is presented, using femtosecond UV pump pulses XUV probe from high harmonic generation. For both molecules molecular core-to-valence lines fade immediately, within pump-probe time-resolution. Absorption converging to atomic product emerge promptly in CH3I but are time-delayed C6H5I. We attribute this delay initial π → σ(*) excitation...

The bi-circular scheme for high harmonic generation, which combines two counter-rotating circular fields with frequency ratio 2:1, has recently permitted to generate harmonics essentially polarization, opening the way ultrafast chiral studies. This produces lines at 3N + 1 and 2 multiples of fundamental driving frequency, while are forbidden owing three-fold symmetry field. It is generally established that routinely observed signals these come from a slight ellipticity in fields, breaks...

Ionization and fragmentation of ${\mathrm{C}}_{60}$ fullerenes is studied in elliptically polarized, intense fs laser fields at 797 nm [$I=(0.5--4.3)\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }\mathrm{W}\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$] contrasted with ${\mathrm{Xe}}^{+}$, utilizing time-of-flight mass spectrometry. Very pronounced changes parent fragment ion yield as a function ellipticity are observed. At lower intensities reduction the for circular polarization...

We report a 30% internal conversion efficiency for the first Stokes pulse in stimulated Raman scattering of femtosecond pulses that are dispersively stretched to 250 ps, obtained by use an all-solid-state laser system. A transfer linear chirp is observed, leading duration 190 fs after recompression. Compressed energies 80 μJ at repetition rate 1 kHz obtained, with potential easy increase more than 150 μJ. The temporal and spectral characteristics pump calculated, results explain observed...

Femtosecond photoexcitation of organic chromophores in a molecular crystal induces strong changes the electronic dipole moment via intramolecular charge transfer as is evident from transient vibrational spectra. The structural response to change mapped directly for first time by ultrafast x-ray diffraction or diffuse scattering. Changes diffracted and transmitted intensity demonstrate an angular rearrangement molecules around excited dipoles following 10 ps kinetics leaving lattice plane...

Experiments and numerical simulation were performed for verification of the role femtosecond pulse chirp supercontinuum generation in photonic crystal fiber. We demonstrate that injection high power negatively chirped pulses near zero dispersion point brings an advantage over positively resulting additional collision between solitons development a significantly broader spectrum. Coupling Raman induced dispersive waves generated by higher order was proven to be key mechanism behind results.

Attosecond (1 as=10-18 s) pulses produced through high harmonic generation (HHG) are a basis for studies of electron dynamics during light-matter interaction on an electron's natural time scale. Extensively exploited HHG technology has, however, few unsolved problems, where producing circularly polarized or chiral attosecond belongs to them. We have demonstrated experimentally way control the ellipticity pulse trains via in two-color, bi-circular laser fields. show that combination nonlinear...

We demonstrate a concept for short x-ray generation at 1kHz repetition rate from thin-foil target in very compact configuration, which allows one, essentially, to decrease the distance between source and investigated object. The scaling hard yield hot electron temperature with pulse intensity are determined best described by power law. useful photon fluxes of 3.4×109 3.3×109phot∕(ssrad) generated Ni- Cu Kα lines, respectively. size was detected be 10μm.