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The generation of high-order harmonics of the ultrashort pulses of Ti:sapphire laser in the plasma plumes produced during laser ablation of various semiconductors (Te, Se, Si, As, Sb, and Ge) is reported. Application of two-color pump allowed the generation of enhanced odd and even harmonics. The resonance-induced enhancement of single harmonics was observed in the Ge, Se, Sb, As, and Te plasmas. The enhanced 35th harmonic obtained from selenium plasma was twelve times stronger than the neighboring harmonics. We also demonstrate the quasi-phase-matching of the harmonics generated in the As plasma. [ABSTRACT FROM AUTHOR]

The systematic studies of the harmonic generation of ultrashort laser pulses in the 5-mm-long Zn and Mn plasmas (i.e., application of nanosecond, picosecond, and femtosecond pulses for ablation, comparison of harmonic generation from atomic, ionic, and cluster-contained species of plasma, variation of plasma length, two-color pump of plasmas, etc.) are presented. The conversion efficiency of the 11th-19th harmonics generated in the Zn plasma was ~5×10-5. The role of the ionic resonances of Zn near the 9th and 10th harmonics on the enhancement of harmonics is discussed. The enhancement of harmonics was also analyzed using the two-color pump of extended plasmas, which showed similar intensities of the odd and even harmonics along the whole range of generation. The harmonics up to the 107th order were demonstrated in the case of manganese plasma. The comparison of harmonic generation in the 5-mm-long and commonly used short (⩽0.5mm) plasma plumes showed the advanced properties of extended media. [ABSTRACT FROM AUTHOR]

We present the studies of the high-order harmonic generation of 802-nm, 64-fs pulses in the extended plasmas contained the carbon-based clusters (fullerenes, nanofibers, nanoparticles, and nanotubes). Our studies show that the 11th-19th harmonics in the 15-33 eV range may originate from the low-sized nanoparticles produced during ablation of large clusters and agglomerates. The conversion efficiency of the 11th harmonic generated from the 5-mm-long fullerene plasma was estimated to be 2×10-5. [ABSTRACT FROM AUTHOR]

We investigate third- and higher-order nonlinear optical processes in Au, Pt, Pd, and Ru nanoparticles. We measured the nonlinear refractive indices and nonlinear absorption coefficients of the suspensions of these nanoparticles using the 792 nm femtosecond and picosecond pulses. The highest values of these parameters were observed in the case of Au nanoparticles (-8×10-14 m2 W-1 and 1.7×10-10 m W-1), when the 210 ps pulses were used as a probe radiation. The high-order harmonic generation was studied during the propagation of the 120 fs pulses through the plasmas produced on the surfaces containing the nanoparticles. The highest harmonic cutoff (33rd order) was observed in the case of gold nanoparticle-contained plasma. These results were compared with the harmonics generating from the plasma produced on the surfaces of the bulk materials of the same origin. A two- to sixfold enhancement of harmonic yield was observed in the case of nanoparticle-contained plumes with regard to the bulk materials. [ABSTRACT FROM AUTHOR]

A pump and probe system is developed, where the probe pulse duration τ is less than 60 fs while the pump pulse is stretched up to 150–670 fs. The time-resolved excitation processes and damage mechanisms in the omnidirectional reflectors SiO2/TiO2 and ZnS/MgF2 are studied. It is found that as the pump pulse energy is higher than the threshold value, the reflectivity of the probe pulse decreases rapidly during the former half, rather than around the peak of the pump pulse. A coupled dynamic model based on the avalanche ionization (AI) theory is used to study the excitation processes in the sample and its inverse influences on the pump pulse. The results indicate that as pulse duration is longer than 150 fs, photoionization (PI) and AI both play important roles in the generation of conduction band electrons (CBEs); the CBE density generated via AI is higher than that via PI by a factor of 102–104. The theory explains well the experimental results about the ultrafast excitation processes and the threshold fluences. [ABSTRACT FROM AUTHOR]

The plateau pattern of the harmonic distribution up to the 65th order (λ=12.24 nm) and the 5×10-7 conversion efficiency were achieved after the propagation of femtosecond pulses through the laser-produced boron plasma. The optimization of high-order harmonics generation was carried out at the focusing conditions when the confocal parameter of fundamental radiation was close to the plasma sizes. A study of cutoff energy showed its dependence on the second ionization potential of nonlinear medium. The spatial distribution of the radiation propagating through the boron plume showed the appearance of ringlike pattern at the intensities exceeding a saturated intensity of singly charged ions. [ABSTRACT FROM AUTHOR]

X-ray absorption measurements at the Ru L3 edge have been used to study the adsorption of Ru3(CO)12 on Cu(100) surfaces at submonolayer and monolayer coverages and the subsequent formation of Ru–Cu bimetallic aggregates at these surfaces. The analysis of the Ru L3 edge x-ray absorption near edge structure (XANES) reveals (a) the surface Ru–Cu bimetallic aggregates are three dimensional clusters of which the Ru atoms are in the ‘‘bulk’’ and the surface of the cluster is covered with Cu atoms, and (b) relative to pure Ru metal, Ru in the bimetallic aggregates gains d character. The chemical properties of these bimetallic surfaces and the effect of the cluster size on their electronic properties revealed by XANES as well as LEED and Auger are also reported. These results are compared with previous results of Ru3(CO)12/Cu(111). The implications of these observations are discussed. [ABSTRACT FROM AUTHOR]

Details a study which examined the epitaxial growth of a silicon thin film by ultrahigh vacuum electron cyclotron resonance plasma chemical vapor deposition. Relationship between cleaning condition of a substrate and the quality of epitaxially grown silicon film; Experimental procedures; Results and discussion.

Develops a new procedure to prepare the clean surface of a silicon single crystal. Tests which proved that prepared surface has a hydrogen monoatomic layer; Effect of hydrogen termination; Manner of removing the oxide layer in a silicon single-crystal held in the air.

Examines the chemical structure and property of fluorine-containing species on the hydrofluoric acid (HF) etched silicon surface. Oxidation rate of HF etched silicon surface; Flourine content on HF etched silicon surface; Chemical reactivity of fluorine-containing species.

Presents a technique for controlling the chemical reactivity of a silicon single-crystal surface through chemical modification with atomic hydrogen. Details on the experiment; Results of the study; Conclusion.

Describes the preparation of diamondlike carbon (DLC) films through electron cyclotron resonance chemical vapor deposition. Properties of DLC; Composition of films deposited at low cavity bias voltage.

Characterizes the evaporated thin films of merocyanine dyes. Vacuum evaporation of merocyanine dyes; Absorption of the dye film on quartz; Difference in color between a film deposited on the bare silicon substrate and one on a quartz glass plate.

Fe–Pt exchange-spring film magnets composed of both order and disorder phases were fabricated by the sputtering method followed by an annealing process, and an increase in thickness was achieved up to 7 μm. The remanence value for the films with the thickness ranging from 1.7 to 7 μm showed approximately 0.9 T which exceeded a theoretical value of 0.7 T for an isotropic Fe–Pt film composed of only order phase. For example, the values of remanence, coercivity, and (BH)max for a 7-μm-thick film were 0.87 T, 490 kA/m, and 118 kJ/m3, respectively. The film also had a superior recoil rate compared to that of a Fe–Pt film composed of only order phase. These results indicate that we can obtain Fe–Pt exchange-spring thick films with good magnetic properties and a recoil rate. [ABSTRACT FROM AUTHOR]

Ru L2,3 edge XANES (x-ray absorption near edge structure) together with AES (Auger electron spectroscopy) and LEED (low energy electron diffraction) studies of Ru3(CO)12 adsorbed on Cu(111) reveal the following: (a) Ru3(CO)12 adsorbs molecularly on Cu(111) at low temperature (<=-50°). (b) Upon electron bombardment, Ru3(CO)12 dissociates to form bare Ru aggregates which exhibit very broad Ru L2,3 white lines and featureless absorption in the XANES spectrum indicating that the Ru atoms are not well ordered on the Cu(111) surface. (c) Annealing of the bare Ru aggregates on Cu(111) at 450 °C results in the formation of Cu/Ru bimetallic clusters in which the Ru atoms are in the core and exhibit bulk-like Ru L2,3 XANES while the surface is covered with Cu atoms. Analysis of the Ru L3 white line intensity indicates that charge redistribution in the Ru d band occurs upon the transformation from the bare Ru aggregates to the bimetallic Cu/Ru clusters on Cu(111). [ABSTRACT FROM AUTHOR]

We demonstrate the technique allowing the fine tuning of the distance between the laser-produced plasma plumes on the surfaces of different materials, as well as the variation of the sizes of these plumes. The modification of plasma formations is based on the tilting of the multi-slit mask placed between the heating laser beam and target surface, as well as the positioning of this mask in the telescope placed on the path of heating radiation. The modulated plasma plumes with the sizes of single plume ranging between 0.1 and 1 mm were produced on the manganese and silver targets. Modification of the geometrical parameters of plasma plumes proved to be useful for the fine tuning of the quasi-phase-matched high-order harmonics generated in such structures during propagation of the ultrashort laser pulses. We show the enhancement of some groups of harmonics along the plateau range and the tuning of maximally enhanced harmonic by variable modulation of the plasma. [ABSTRACT FROM AUTHOR]

We demonstrate the harmonic generation of the femtosecond pulses propagated in the vicinity of solid targets. The harmonics were observed in the case of double-pulse scheme while using different solids (metals, nanoparticle, and microparticle powders). The efficiency and cut-off of harmonic generation using double-pulse scheme were varied depending on the target and compared with the commonly used method of the laser ablation by the picosecond pulses. The simplicity of this method allows its application in the nonlinear spectroscopy of solids. [ABSTRACT FROM AUTHOR]

We demonstrate the advanced properties of extended plasma plumes (5 mm) for efficient harmonic generation of laser radiation compared with the short lengths of plasmas (~0.3-0.5 mm) used in previous studies. The harmonic conversion efficiency quadratically increased with the growth of plasma length. The studies of this process along the whole extreme ultraviolet range using the long plasma jets produced on various metal surfaces, particularly including the resonance-enhanced laser frequency conversion and two-color pump, are presented. Such plasmas could be used for the quasi-phase matching experiments by proper modulation of the spatial characteristics of extended ablating area and formation of separated plasma jets. [ABSTRACT FROM AUTHOR]

The optical design and mechanical solution for a soft x-ray beamline BL-7A in PF-KEK for the energy range 10-1000 eV with a PGM are described. The optical characteristics of the beamline are tested with gas phase absorption and photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

A crystal cooling system was designed and tested successfully for the soft x-ray double-crystal monochromator in an ultrahigh-vacuum environment at the Photon Factory. The temperature rise at the surface of the InSb first crystal is reduced to less than 45 °C at an average stored current of 200 mA. With the help of a control software, the output beam can be fixed in a position for a wide energy range. In this paper, the heating effect on the double-crystal monochromator, and the design and performance of a water cooling system are described. [ABSTRACT FROM AUTHOR]

The design and performance of a compact, ultrahigh vacuum (UHV) compatible x-ray detector is described which can be applied to measurements of surface EXAFS spectra and x-ray standing wave (SW) profiles. The detector is a type of gas flow proportional counter. Its compactness allows us to save space around the sample. A 25-μm-thick beryllium window separates UHV ( < 1 × 10[sup -10] mbar) environment from atmospheric pressure and provides good efficiency to detect low energy x rays. Surface EXAFS spectra of less than 061 monolayer chlorine on a Ni substrate are successfully measured with high quality. Its high signal-to-background ratio allows us to measure SW profiles, which could hardly be obtained with any electron yield detection technique. [ABSTRACT FROM AUTHOR]

We demonstrate a considerable broadening of the harmonics generating in laser plasma using the laser pulses propagating through the filaments in air. A fourfold increase of harmonic bandwidth was achieved in the case of phase-modulated laser pulses, alongside with an increase in harmonic conversion efficiency (from 5×10-6 to 1.2×10-5). We also present the studies of harmonic generation using phase-modulated pulses at different ranges of ellipticity of the polarization of laser beam. [ABSTRACT FROM AUTHOR]

We observed the extended harmonic spectra generated in the Cd and Cr plasmas. The mechanism of harmonic extension was attributed to the harmonic generation in doubly charged particles and the influence of broadband ionic resonances in the range of 20–25 nm. The extension of harmonic cutoff up to the 73rd (Cd) and 83rd (Cr) orders was achieved. [ABSTRACT FROM AUTHOR]

Uniform ZnSe nanowires are observed on the ablation crater on ZnSe crystal surface irradiated by femtosecond lasers in air, while other parts of the sample surface are not polluted. The nanowire growth rate is about 5 μm/s, it is higher than that fabricated by chemical vapor deposition method by a factor of 104. The nanowire length and diameter can be controlled by varying laser pulse energy and pulse number. The formation mechanism is studied and found to be self-catalyzed vapor-liquid-solid process. [ABSTRACT FROM AUTHOR]

Nanoripples with periods of 150 and 80 nm are formed on the surface of 6H-SiC crystals irradiated by the p-polarized 800 nm and the s-polarized 400 nm femtosecond lasers, respectively. When both of the two collinear laser beams focus simultaneously on the sample surface, nanoparticles are formed on the whole ablation area, and they array in parallel lines. We propose and confirm that the second harmonics in the sample surface excited by the incident lasers plays an important role in the formation of nanostructures. [ABSTRACT FROM AUTHOR]

The generation of up to the 33rd harmonic (λ=24.12 nm) of a Ti:sapphire laser pulse using prepulse-produced chromium plasma as a nonlinear medium was demonstrated. A steep decrease of intensity for low-order harmonics (up to the 15th order) was followed by a plateau. A considerable restriction of 27th harmonic generation was observed in different focusing conditions. [ABSTRACT FROM AUTHOR]

Sol-gel silica glasses are good nanoporous matrices and are able to confine various phosphors as dopants, so these are quite interesting and strategic materials and show phenomena such as surface-enhanced quantum confinement effects: high luminescence quantum efficiency and ultrafast decay times. We observed directly clear images of metal complex nanoparticles in those with transmission electron microscopy. This can easily improve the quality of uniformly doped sol-gel silica glasses. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optical and mechanical design of a VUV beamline BL-7B in PF-KEK are presented. The optical characteristics are discussed by use of the data of gas absorption spectrum and those of photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]