Synthesis of Silver Nanoparticles by the Ion Implantation Method and Investigation of their Optical Properties

We have investigated the process of metal nanoparticle (NP) synthesis in SiO₂ by implanting Ag₊ ions with an energy of 30 keV depending on the dose ((2–8)·10¹⁶ cm⁻²) and the ionic current density (4–15 µA/cm²). Analysis of the composite materials formed was performed with the use of optical spectroscopy and atomic-force microscopy (AFM). The NPs synthesized in the glass demonstrate a characteristic absorption line associated with the surface plasma resonance effect. A correlation of the spectral shift of the lines caused by a change in the NP size with the diameter of the hemispherical asperities on the SiO₂ surface registered by the AFM method has been revealed. It has been found that for the case of a fixed current density in the ion beam the silver NP sizes remain practically unaltered with increasing ion dose up to a certain value (6·10¹⁶ cm⁻²), and only an increase in the concentration of NPs is observed thereby. However, a further increase in the dose causes a decrease in both the NP density and size. On the other hand, at a fixed high dose an increase in the ionic current density leads to a gradual enlargement of the NPs. We have considered the mechanisms explaining the change in the NP sizes with increasing dose and ionic current density and evaluated the possibilities of carrying out controlled synthesis by varying the implantation conditions.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 218–223, March–April, 2005.     

The “SKATE” CO2 Gigawatt Laser for a Laser-Plasma Generator of Ions and Nuclei

A set-up of the CO₂ SKATE and its output characteristics are described. The system is based on a self-sustained gas discharge module with x-ray preionization that ensures reliability and stable repetition rate operation at 1 Hz for a long time. Measurement of the initial electron density in the discharge volume produced by an x-ray gun is presented for different gases and their mixtures, which is of independent interest for some applications of x-ray preionization. Data on measurements of the low-intensity signal gain and laser parameters for a free-running generator configuration are presented as well as long-term operation characteristics. This laser system has been used as a CO₂ generator with gigawatt peak intensity and high spatial–temporal characteristics. In particular, the laser can be used as a driver for a source of multicharged ions in contrast to the laboratory prototypes previously investigated.     

Electron spin resonance in the spin-1/2 quasi-one-dimensional antiferromagnet with Dzyaloshinskii-Moriya interaction BaCu2Ge2O7

We have investigated the electron spin resonance (ESR) on single crystals of BaCu2Ge2O7 at temperatures between 300 and 2 K and in a large frequency band, 9.6-134 GHz, in order to test the predictions of a recent theory, proposed by Oshikawa and Affleck (OA) [Phys. Rev. Lett. 82, 5136 (1999)]], which describes the ESR in a spin-1/2 Heisenberg chain with the Dzyaloshinskii-Moriya interaction. We find, in particular, that the ESR linewidth, Delta H, displays a rich temperature behavior. As the temperature decreases from T(max)/2 approximately 170 to 50 K, Delta H shows a rapid and linear decrease, Delta H approximately T. At low temperatures, below 50 K, Delta H acquires a strong dependence on the magnetic field orientation and for H axially c it shows a (h/T)(2) behavior which is due to an induced staggered field h, according to OA's prediction.     

Saturated absorption and nonlinear refraction of silicate glasses doped with silver nanoparticles at 532 nm

The nonlinear optical characteristics of silicate glasses doped with silver nanoparticles are investigated by Z-scan technique using second harmonic radiation of picosecond Nd:YAG laser (=532 nm, =55 ps). The real and imaginary parts of third-order nonlinear susceptibility of silver-contained glasses were measured. It was found that the sign of Im ⁽³⁾was negative due to saturated absorption and the sign of Re ⁽³⁾ was changed from negative (self-defocusing) to positive (self-focusing) with growth of laser radiation intensity. The mechanisms responsible for saturated absorption and nonlinear refraction are discussed.     

Optimal generation of single-dispersion precompensated 1-fs pulses by molecular phase modulation

We show how an optimal control approach can be combined with the pump-probe technique for pulse compression by molecular phase modulation in hollow-core fibers to generate single 1-fs pulses in the visible. Varying the intensity and duration of the Gaussian-shaped pump pulse at the input induces optimal rotational response of the molecules. The probe pulse, which scatters off of the resulting time variation of the refractive index, is shaped at the input for optimal compression at the output, including dispersion to all orders.     

Molecule without electrons: binding bare nuclei with strong laser fields

We show how a carefully chosen combination of strong linearly and circularly polarized laser fields can bind two same-sign charges, not only suppressing their Coulomb repulsion in all three spatial dimensions, but also creating an effective attraction. As an example, we show how a molecule HD2+ stripped of both electrons can be kept bound by the laser fields.