Optical detection of attosecond ionization induced by a few-cycle laser field in a transparent dielectric material

We observe an optical signature induced by the modulation of electron density inside a bulk transparent solid that is quasiperiodically ionized on an attosecond time scale by electric field peaks of a focused few-cycle laser pulse. The emitted optical signal resulting from the attosecond ionization dynamics is spatially, temporally and spectrally isolated from concomitant optical responses through the use of a noncollinear pump-probe technique. The method holds promise for developing an attosecond metrology for bulk solids, in which, unlike in the established attosecond metrology of gases and surfaces, direct detection of charged particles is unfeasible.     

Degradation of Orange II by heterogeneous photocatalytic reaction using montmorillonite KSF

Degradation of Orange II in montmorillonite KSF (KSF) suspensions under irradiation by a 250 W metal halide lamp (λ ≥ 365 nm) was investigated. The degradation kinetics of Orange II in KSF suspensions followed the Langmuir-Hinshelwood model. The effects of KSF concentration, solution pH, initial Orange II concentration, carboxylic salts were studied.     

Photochemistry of the IrCl<Subscript>6</Subscript><Superscript>2−</Superscript> complex in aqueous solutions in the presence of the bromide anions

Laser flash photolysis (308 nm) was applied to study photochemistry of the IrCl₆ ²⁻ complex in aqueous solutions in the presence of the Br⁻ anions. The formation of the Br₂ ^·− radical anions in the reaction between the Br⁻ ion and secondary radical pair formed after the photon absorption by the initial complex was observed. The Br₂ ^·− radical anions decay both in recombination and in the reaction with the initial IrCl₆ ²⁻ complex.     

Sub-5-pm linewidth, 130-nm-tuning of a coupled-cavity Ti:sapphire oscillator via volume Bragg grating-based feedback

A novel coupled-cavity Ti:sapphire oscillator architecture featuring a volume Bragg grating as a feedback element is presented. The oscillator provides continuous wave lasing within a spectral linewidth as narrow as 5 pm. The output can be wavelength-tuned over an ultrabroad spectral range of 130 nm, extending from 714 to 842 nm. This unique combination of narrow spectral linewidth and wide tuning range makes the laser suitable for applications such as sensing and Raman and absorption spectroscopy. The laser also displays ideal TEM₀₀ mode operation throughout its tuning range with output powers beyond 300 mW. Detailed studies of the cw lasing dynamics across the wide tuning range are described. The general architecture of this design can be implemented for high resolution tuning across the broad spectral emission bands of other solid state lasers with single mode operation.     

On extremal hypergraphs for Hamiltonian cycles

We study sufficient conditions for Hamiltonian cycles in hypergraphs, and obtain both Turán- and Dirac-type results. While the Turán-type result gives an exact threshold for the appearance of a Hamiltonian cycle in a hypergraph depending only on the extremal number of a certain path, the Dirac-type result yields a sufficient condition relying solely on the minimum vertex degree.     

Evidence for stratification of deuterium-tritium fuel in inertial confinement fusion implosions

Measurements of the D(d,p)T (dd) and T(t,2n)(4)He (tt) reaction yields have been compared with those of the D(t,n)(4)He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.     

Channeling and electromagnetic radiation of relativistic charged particles in metal-organic frameworks

We have developed the theory of electromagnetic interaction of relativistic charged particles with metal-organic frameworks (MOFs). The electrostatic potential and electron number density distribution in MOFs were calculated using the most accurate data for the atomic form factors. Peculiarities of axial channeling of fast charged particles and various types of electromagnetic radiation from relativistic particles has been discussed.     

Role of bromine on the thermal and optical properties of photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is a photosensitive silicate glass doped with cerium, silver, and fluorine. The precipitation of a minor crystalline phase after UV-exposure and thermal treatment induces a refractive index change, which is large enough to create diffractive optical elements. In this work we present a first attempt to understand the role of bromine on thermal and optical properties of PTR glass. We reveal that at least 75% of the concentration of bromine of commercial PTR glass is necessary to produce photo-induced crystallization. We also show that an increase of the bromine concentration will increase the mean refractive index of virgin PTR glass. Further thermal treatments induce a decrease of the mean refractive index of PTR glass. This decrease is finally shown to be larger in UV-exposed glass if photo-induced crystallization is present. We also show that bromine concentration will decrease water concentration in PTR glass and have an impact on the losses in visible. We demonstrate that the higher the bromine concentration, the higher the shift of the silver containing particles absorption band. In addition, if bromine concentration is high enough to produce photosensitivity, an increase of scattering due to the crystallization process is observed.     

Efficient power scaling of laser radiation by spectral beam combining

The possibility of achieving multikilowatt laser radiation by spectrally combining beams using volume Bragg gratings (VBGs) is shown. The VBGs recorded in a photothermorefractive glass exhibit long-term stability of all its parameters in high-power laser beams with power density >1 MW/cm2 in the cw beam of total power on a kilowatt level. We consider an architecture-specific beam-combining scheme and address the cross-talk minimization problem based on optimal channel positioning. Five-channel high efficiency spectral beam combining resulted in a >750 W near-diffraction-limited cw beam has been demonstrated experimentally.     

High-areal-density fuel assembly in direct-drive cryogenic implosions

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2]. Neutron-averaged areal densities of 202+/-7 mg/cm2 and 182+/-7 mg/cm2 (corresponding to estimated peak fuel densities in excess of 100 g/cm3) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuel adiabat can be accurately controlled under ignition-relevant conditions.