Self-organized nanogratings in glass irradiated by ultrashort light pulses

Periodic nanostructures are observed inside silica glass after irradiation by a focused beam of a femtosecond Ti:sapphire laser. Backscattering electron images of the irradiated spot reveal a periodic structure of stripelike regions of approximately 20 nm width with a low oxygen concentration, which are aligned perpendicular to the laser polarization direction. These are the smallest embedded structures ever created by light. The period of self-organized grating structures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. The phenomenon is interpreted in terms of interference between the incident light field and the electric field of the bulk electron plasma wave, resulting in the periodic modulation of electron plasma concentration and the structural changes in glass.     

Absolute differential cross sections for photo double ionization of helium from the Ab initio hyperspherical R-matrix method with semiclassical outgoing waves

The hyperspherical R-matrix method with semiclassical outgoing waves introduced by us previously [Phys. Rev. A 60, 3667 (1999)] is applied to the one-photon double ionization of the He atom. The absolute differential cross sections obtained are in excellent agreement with experiment for the very challenging dynamical situations considered. This method is the first one to compute the final double continuum state accurately over the entire configuration space, from the vicinity of the nucleus to the asymptotic region.     

Effect of Mn and Fe on the reactivity of sulfated zirconia toward H2 and n-butane: a diffuse reflectance IR spectroscopic investigation

Sulfated zirconia (SZ) and sulfated zirconia promoted with 2 wt % manganese (MnSZ) or iron (FeSZ), all active in n-butane isomerization, were investigated using diffuse reflectance Fourier transform IR spectroscopy (DRIFTS). By adsorption of H(2) at 77 K or of n-butane at room temperature, it was found that the promoters neither enhance the Lewis nor the Br?nsted acid strength. SZ and promoted SZ do not exhibit higher acid strength than zeolites. In a batch experiment using 70 hPa of H(2), SZ did not react at 473 K. Reaction of H(2) with MnSZ produced water (band at 5242 cm(-1)) and a decrease in the sulfate groups (multiple bands). Heating of SZ in 10 hPa n-butane to 573 K caused total reduction of sulfate to H(2)S (2583, 2570 cm(-1)) and partial and total oxidation of butane to olefinic species (3062 cm(-1)), CO(2), and water. MnSZ and FeSZ reacted with n-butane already at 373 K; products of skeletal isomerization (methyne CH vibration at 2910 cm(-1)) were detected and sulfate groups were consumed. Rather than increasing the acidity, the promoters enhance the oxidation potential of sulfate and facilitate alkane activation via oxidative dehydrogenation.     

Angle-resolved electron spectroscopy of laser-assisted Auger decay induced by a few-femtosecond x-ray pulse

Two-color (x-ray+infrared) electron spectroscopy is used for investigating laser-assisted KLL Auger decay following 1s photoionization of atomic Ne with few-femtosecond x-ray pulses from the Linac Coherent Light Source. In an angle-resolved experiment, the overall width of the laser-modified Auger-electron spectrum and its structure change significantly as a function of the emission angle. The spectra are characterized by a strong intensity variation of the sidebands revealing a gross structure. This variation is caused, as predicted by theory, by the interference of electrons emitted at different times within the duration of one optical cycle of the infrared dressing laser, which almost coincides with the lifetime of the Ne 1s vacancy.     

Femtosecond laser direct processing in wet and dry silica glass

The infrared femtosecond laser damage threshold is found to be independent of OH content in pure silica glass. Additionally, the density and the mean trapping time of electrons excited in the conduction band are also found to be independent on OH concentration.     

State and properties of ion-exchanged cations in zeolites: 1. IR spectra and chemical activation of adsorbed molecular hydrogen

Adsorption isotherms and of adsorbed molecular hydrogen indicate that H₂ is weakly adsorbed by alkali-metal forms of faujasites, mordenite, and high-silica zeolite ZSM-5. The alkaline-earth forms of the same zeolites adsorb hydrogen somewhat more strongly; nevertheless, the hydrogen molecules adsorbed by the barium form of mordenite are in the hindered rotation state. Molecular hydrogen is most strongly adsorbed by the zinc and cadmium forms of the high-silica zeolite. In this case, molecular hydrogen is strongly polarized and undergoes heterolytic dissociative adsorption, yielding acidic hydroxyl groups and cation-bound hydride ions.     

Gas-dynamic disturbances created by surface dielectric barrier discharge in the constricted mode

Three-dimensional structure of the gas-dynamic disturbances, created by surface dielectric barrier discharge in a constricted (saturated) mode, was analyzed simultaneously with the discharge morphology. Discharge was created in the still air under normal conditions. Flow visualization was performed by shadowgraphy and stereo-PIV technique. The wall-normal jets with the origins located in between the positions of the constricted filaments are found. Velocity magnitude in the wall-normal direction is comparable with the tangential component. Flow structure is similar to the one created by the serpentine actuator.