High order harmonic generation by non-linear reflection of a pedestal-free intense laser pulse on a plasma

We demonstrate the influence of the prepulses and ASE of ultrashort pulses interacting with a solid target by addressing the direct comparison of the harmonic spectra generated by reflection onto a solid target with and without the introduction of a plasma mirror system. Harmonics up to the 20th of the fundamental of the Ti-Sa laser are clearly visible in a situation free from any plasma expansion. PACS 42.65. Ky; 52.38.-r; 52.38.Ph; 52.50.Jm     

Applications of nanodiamonds for separation and purification of proteins

Recombinant apoobelin and recombinant luciferase are separated from bacterial cells of Escherichia coli with the use of detonation nanodiamonds. The application of nanodiamonds has a number of points in its favor, namely, (i) simplifies the procedures for purifying the proteins, (ii) decreases the time of their separation to 30–40 min, (iii) eliminates the necessity of using special chromatographic equipment, and (iv) makes it possible to prepare high-purity apoobelin and luciferase materials with protein yields of 35–45 and 45–60%, respectively. The possible mechanisms of interaction of protein molecules and nanodiamond particles are analyzed.     

Anomalies in the magnetic and magnetoelastic properties of Sm<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> single crystals (<Emphasis Type="Italic">x</Emphasis> ∼ 0.5) at phase transitions

By studying the magnetic and magnetoelastic properties, it is established that, as the temperature is lowered, Sm_1?xSr_xMnO₃ single crystals (x=0.5, 0.55) undergo spontaneous phase transitions from the paramagnetic to a local charge-ordered state at T_co=220 K and to an A-type antiferromagnetic state at T_N=175 K. It is shown that strong magnetic fields (H_cr ～ 200 kOe) break up the antiferromagnetic order and charge ordering and drive a phase transition to a conducting ferromagnetic state. H-T phase diagrams are constructed for single crystals with x=0.5 and 0.55.     

Defect formation in Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>/Ge(111) epitaxial heterostructures

Selective chemical etching and transmission electron microscopy are used to study the defect formation in Ge_1?xSi_x/Ge(111) epitaxial heterostructures at 0.01<x<0.35. As the Si content in the solid solution (SS) increases, the dislocation densities in the epitaxial layer, at the interface, and in the near-interface region in the substrate are found to vary nonmonotonically. The difference in the depth distribution of dislocations observed in the heterostructures in three different SS composition ranges is caused by the effect of the SS composition on the kinetics of misfit-stress relaxation, in particular, on the intensity of misfit-dislocation generation and multiplication. It is found that, in the heterostructures grown by hydride epitaxy at 600°C, misfit-dislocation multiplication through a modified Frank-Read mechanism occurs only in the range 0.03<x<0.20. The results obtained are explained in the context of the effect of silicon-rich microprecipitates, which form during the spinodal decomposition of the SS, on dislocation generation and motion in the epitaxial layer. A mechanism is proposed for misfit-dislocation generation by heterogeneous sources in the epitaxial layer; the mechanism is based on the generation of interstitial dislocation loops near microprecipitates.     

Hyperfine Interactions in Pb<Superscript>3+</Superscript>F<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack>F<Stack><Subscript>a</Subscript><Superscript>−</Superscript></Stack> clusters in fluorite crystals

The parameters of hyperfine interactions in Pb³⁺F ₈ ^? F _a ^? tetragonal clusters of MeF₂ crystals (Me=Ca, Sr, Ba) are interpreted. The contributions of the spin polarization to the parameters of the proper hyperfine interaction and additional (ligand) hyperfine interactions are calculated in the approximation of weak binding between a charge-compensating ion F _a ^? and a cubic fragment in the tetragonal cluster. It is demonstrated that correct inclusion of the contributions from the spin polarization to the ligand isotropic hyperfine interaction for the F _a ^? ion leads to anomalously large parameters of this interaction for MeF₂ crystals. These results are in agreement with experimental data.     

Electron transition in intercalated disulfide CuCrS<Subscript>2</Subscript>

Electrical, resonant, and magnetic properties of intercalated copper chromium disulfide CuCrS₂ are studied. It is established that CuCrS₂ is an antiferromagnetic semiconductor with Néel temperature T_N=40.7 K and an effective magnetic moment of 4.3µ_B. Anomalies in the electrical, magnetic, and resonant properties of CuCrS₂ are found at T_c=110 K, which suggest an electron transition accompanied by alteration of the valences of the 3d-metal ions.     

Optical investigations of the effect of gradual substitution NH<Subscript>4</Subscript> → Cs on the ferroelastic phase transition in a CsLiSO<Subscript>4</Subscript> crystal

Crystals of Cs_x(NH₄)_1?xLiSO₄ (0.39≤x≤1.0) solid solutions are grown and investigated using polarized light microscopy and measurements of the birefringence in the temperature range 100–530 K. The (x-T) phase diagram of the Cs_x(NH₄)_1?xLiSO₄ solid solutions is constructed. It is demonstrated that, upon substitution of ammonium for cesium in the CsLiSO₄ crystal, the phase transition temperature gradually increases to such a degree that the ferroelastic phase can exist at room temperature. The triple point of intersection of the Pmcn, P2₁cn, and P112₁/n phase boundaries is determined. It is established that the introduction of ammonium in small amounts has an unusually strong effect on the refractive properties and character of the ferroelastic phase transition in the CsLiSO₄ crystal.     

Spectroscopic ellipsometry study of liquid crystal and polymeric thin films in visible and near infrared

In this work, we propose spectroscopic ellipsometry as a suitable method for measuring optical properties in soft materials, polymers and liquid crystals, specially selected for use in photonics applications. We show the results of our measurements on some multilayered samples, in the range from visible to the near-IR region, of interest for telecom applications. We point out potentialities and limits of the technique and compare the obtained results with another experimental method, the m-lines spectroscopy, and/or with existing data in the literature. The results about the optical parameters for the analysed materials (the nematic liquid crystal 5CB, one commercial and one lab made optical polymer, and an Indium Tin Oxide film) are useful and interesting by themselves. In fact, as a paradigmatic example, we briefly discuss how an incomplete knowledge of this kind of data can lead to a wrong design of a Bragg grating device. However, more than in the provided data, we put the interest of the present analysis in the warnings about spectroscopic ellipsometry utilization and eventually the necessity of getting complementary information.Received: 13 May 2004, Published online: 29 June 2004PACS: 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) - 78.66.Qn Polymers; organic compounds - 07.60.Fs Polarimeters and ellipsometers     

Relaxation of photoexcited Na$_\mathsf{3}$F

This paper describes the spectroscopy of Na₃F both in the frequency and time domains. The photoionization efficiency curve shows two thresholds, associated to two isomers. The excited electronic states of the C_2v isomer have been probed by photodepletion spectroscopy, and the results are used to analyze a time-resolved study of photoexcited Na₃F, probed by photoionization. The pump-probe signal clearly shows damped oscillations, the period of which is fitted to fs, close to twice the previously measured bending mode of Na₂F [1], while the relaxation time is fs.Received: 31 October 2003, Published online: 6 January 2004PACS: 36.40.Qv Stability and fragmentation of clusters - 33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)