Study of the relaxation of metastable 6p 3 2 D 3 2/0 states of bismuth atoms in a bismuth-vapor laser

A universal absorption technique for studying the kinetics of relaxation of atomic states in the afterglow of a repetitively pulsed discharge in metal vapor lasers is proposed. It uses the measurement of the absorption of narrowband emission of a tunable dye laser and numerical simulation of absorption. The relaxation of metastable 6p ^{3 2} D ₃ ^2/0 states of Bi atoms in the afterglow of a 472.2-nm bismuth vapor laser was studied. The prepulse values of the concentration of metastable atoms n _m were not higher than 10¹¹ cm^?3 and did not impede the improvement of laser characteristics. The afterpulse values of n ^m were ～10¹³ cm^{? 3}.     

Effect of radiation dose on the size of bismuth particles produced by radiolysis

Colloidal bismuth is formed in -irradiated solutions , containing BiO⁺, 0.2 M propanol-2 and 2×10^-2 M of polyacrylic acid. Radiolytic reduction of these solutions produces long-lived bismuth clusters which are stabilized on the polymer chains. The clusters have a distinct absorption band at 350 nm with a tentatively assigned to or structures. With continued irradiation, the clusters coalesce into colloidal particles of 5 nm diameter. The absorption spectra of Bi oligomers and colloidal particles are reported as well as the optical changes accompanying their formation.     

Phonon autoecho in bismuth and antimony single crystals

Phonon autoecho is observed upon pumping Bi and Sb semimetals with ultrashort high-energy laser pulses. The autoecho is manifested as a revival of reflection oscillations generated by an A_1g coherent phonon after their complete disappearance. The phenomenon of phonon autoecho offers decisive evidence of the nonclassical character of the state of the crystal lattice that is accomplished in pumping-probing experiments by femtosecond laser pulses.     

Quasi-two-dimensional metallic hydrogen in diphosphide at a high pressure

The average optical reflectivity of bismuth as a function of time t after irradiation by a short laser pulse has been calculated. The amplitude A of photoinduced oscillations in the average optical reflectivity is shown to have extrema under certain conditions. The time τ_j (j is a natural number) at which the amplitude A reaches the jth extremum has been calculated. The calculated dependences of the times τ₁ and τ₂ at which, respectively, the first and second extrema (the first minimum and the first maximum) of the amplitude A are reached on the maximum laser pulse energy density Q are consistent with the experimental data from [8].     

Decay of photoinduced oscillations of the optical reflection coefficient of bismuth

A model describing the decay of photoinduced oscillations of the optical reflection coefficient R of bismuth is constructed, taking the crystal lattice anharmonicity into account. The decay time of oscillations of R is calculated as a function of the energy density of a laser pulse. The results of calculations explain the experimental data on the anomalously strong decay of oscillations of the optical reflection coefficient of bismuth (the decay time decreases by more than an order of magnitude with an increase in the laser pulse energy density from 0 to 4 mJ/cm²).     

STM and XPS investigations of bismuth islands on HOPG

The growth of bismuth thin films on highly oriented pyrolitic graphite (HOPG) was studied using ultra high vacuum (UHV) scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The locations of the main XPS peaks, and also the plasmon energy, are in good agreement with results recorded on bulk bismuth. The shape of the Bi 4f doublet, as well as the well developed Fermi edge, indicates the metallic character of the deposited film. One of the observed shoulders is identified with a quantum-well subband characteristic of thin bismuth films. There is no evidence for the existence of Bi–C bonds, consistent with weak bonding between the Bi islands and the HOPG. The height of the islands and their crystallographic orientation were investigated as a function of surface coverage. The Bi islands grow with the (110) plane parallel to the substrate. The observed heights (3, 5, 7, 9 ML) indicate that the preferred crystal structure involves paired layers on an intermediate mono-atomic Bi layer. There is evidence both for and against the Black Phosphorus like allotrope, and the nature of both the layer pairing and the intermediate layer are yet to be resolved. The islands exhibit stripes oriented along the $<1\overline{1}0>$ axis of the Bi crystal, which is a fast growth direction due to the existence of strongly bonded zig-zag chains of atoms. The surface unit cell and the parameters of the rhombohedral bulk unit cell are estimated based on atomic resolution images. In the case of 2 ML stripes on top of a 5 ML base, the expansion of the outer atomic rows was estimated at 27%. Asymmetries in the growth of the islands are observed. Based on low coverage depositions at reduced substrate temperatures, it is proposed that there is a second fast growth direction corresponding to preferential attachment of atoms to one of the faces of the asymmetric, rhombic cross-section of the (110) crystal.     

Optical effects caused by coincidence between the energies of the plasma oscillations and the band-to-band transition in bismuth crystals doped with an acceptor impurity

The energy of plasma oscillations of free charge carriers in bismuth crystals ?ω_p can be qual to the band gap at the L point of the Brillouin zone E _gL as a result of doping with an acceptor impurity. Variation in the edge shape and splitting of the minimum in the plasma reflection are observed in experimental studies of reflection under normal incidence of radiation on the crystal. An analysis of the totality of available experimental data shows that the above special features are caused by interaction of elementary excitations (such as the plasma oscillations) with band-to-band transitions. It became possible for the first time to ascertain the composition of the bismuth crystals for which the condition ?ω_p=E _gL is satisfied and observe the variation in the characteristics of the plasma oscillations of free charge carriers, which occurs as a result of electron-plasmon interaction.     

Static recording characteristics of new type super-resolution near-field structure

A novel super-resolution near-field optical structure (super-RENS) with bismuth (Bi) mask layer is proposed in this paper. Static optical recording tests with and without super-RENS are carried out using a 650-nm semiconductor laser at recording powers of 14 and 7 mW with pulse duration of 100 ns. The recording marks are observed by high-resolution optical microscopy with a charge-coupled device (CCD)camera. The results show that the Bi mask layer can also concentrate energy into the center of a laser beam at low laser power similar to the traditional Sb mask layer. The results above are further confirmed by another Ar+ laser system. The third-order nonlinear response induced by the plasma oscillation at the Bi/SiN interface during laser irradiation can be used to explain the phenomenon. The calculation results are basically consistent with our experimental results.     

Development of an optical time scale

A time standard based on the use of an optical oscillation period of a frequencystable He–Ne laser as a time scale is first described. We obtained highly frequency-stable oscillations in the SHF range that were locked to the oscillations of a He–Ne laser stabilized to an absorption resonance in methane at 3.39 m. A direct comparison of frequency stabilities of a rubidium standard and He–Ne/CH₄ laser has been made. The absolute measurement of the frequency of the He–Ne/CH₄ laser we performed gave a new value of frequency.This work was reported at the 3rd Frequency Standards and Metrology Symposium     

XPS investigation of LPE garnet films

XPS spectra of YIG, YIG:Bi, YIG:Ca and YIG:Co(Ge, Ca) epitaxial garnet films were measured at room temperature. The positions of the main iron, yttrium, oxygen, bismuth, cobalt and lead spectral lines were determined and their changes with the surface treatments were investigated. It was found that divalent and trivalent states of iron and cobalt ions can be resolved, the chemical shifts being in oposite directions.The authors would like to thank Dr. J. imová for careful EPMA analysis of the samples.     

Theoretical calculations on structural and electronic properties of BGaAsBi alloys

The structural and electronic properties of cubic B _x Ga_1?x As_1?y Bi _y alloys with bismuth (Bi) concentration of 0.0625, 0.125, 0.1875 and 0.25 are studied with various boron (B) compositions by means of density functional theory (DFT) within the Wu-Cohen (WC) exchange correlation potential based on generalized gradient approximation (GGA). For all studied alloy structures, we have implemented geometric optimization before the volume optimization calculations. The obtained equilibrium lattice constants and band gap of studied quaternary alloys are investigated for the first time in literature. While the lattice constant behavior changes linearly with boron concentration, increasing small amount of bismuth concentration alter the lattice constant nonlinearly. The present calculation shows that the band gap decreases with increasing bismuth concentration and direct band gap semiconductor alloy became an indirect band gap with increasing boron concentration. From the band offset calculation we have shown that increasing B and Bi concentration in host GaAs reduced the valance band offset in a heterostructure formed by GaAs and studied alloys.     

Element selective X-ray magnetic circular and linear dichroisms in ferrimagnetic yttrium iron garnet films

X-ray magnetic circular dichroism (XMCD) was used to probe the existence of induced magnetic moments in yttrium iron garnet (YIG) films in which yttrium is partly substituted with lanthanum, lutetium or bismuth. Spin polarization of the 4d states of yttrium and of the 5d states of lanthanum or lutetium was clearly demonstrated. Angular momentum resolved d-DOS of yttrium and lanthanun was shown to be split by the crystal field, the two resolved substructures having opposite magnetic polarization. The existence of a weak orbital moment involving the 6p states of bismuth was definitely established with the detection of a small XMCD signal at the Bi M₁-edge. Difference spectra also enhanced the visibility of subtle changes in the Fe K-edge XMCD spectra of YIG and {Y, Bi}IG films. Weak natural X-ray linear dichroism signatures were systematically observed with all iron garnet films and with a bulk YIG single crystal cut parallel to the (1 1 1) plane: this proved that, at room temperature, the crystal cannot satisfy all requirements of perfect cubic symmetry (space group: ), crystal distortions preserving at best trigonal symmetry ( or R3m). For the first time, a very weak X-ray magnetic linear dichroism (XMLD) was also measured in the iron K-edge pre-peak of YIG and revealed the presence of a tiny electric quadrupole moment in the ground-state charge distribution of iron atoms. Band-structure calculations carried out with fully relativistic LMTO-LSDA methods support our interpretation that ferrimagnetically coupled spins at the iron sites induce a spin polarization of the yttrium d-DOS and reproduce the observed crystal field splitting of the XMCD signal.     

Lifetime of optical phonons in fs-laser excited bismuth

This paper presents experimental and theoretical results on the temperature-dependent optical response of a single crystal of bismuth to excitation by femtosecond laser pulses. We demonstrate that the measured damping rate of the transient reflectivity oscillations relates to the lifetime of optical phonons. The lifetime is the inverse rate of the decay of optical phonons into two acoustic phonons. This lifetime also indicates the approach to the vibration instability (catastrophe) threshold that manifests the beginning of the disordering of a solid crystal and transition to a liquid state. We observe the red shift of phonon frequency, which increases with the rise of the initial lattice temperature. The red shift is different from the previously observed red shift proportional to the electron temperature, and thus to the excitation laser fluence. The coherent phonon excitation process imprinted into the initial change in the reflectivity and the following reflectivity oscillations allowed us to uncover the temporal phonon history preceding the structural transformation of solid Bi.     

Manifestations of Surface States in the Longitudinal Magnetoresistance of an Array of Bi Nanowires

The longitudinal magnetoresistance of the array of parallel-oriented bismuth nanowires each 100 nm in diameter grown by electrochemical deposition in nanopores of an Al₂O₃ membrane has been studied in magnetic fields up to 14 T and at temperatures down to 0.3 K. The resistance increases with the field and reaches a broad maximum in fields about 10 T. An anomalous increase in the resistance in weak fields is qualitatively consistent with the suppression of the antilocalization correction to the resistance, and the maximum is qualitatively associated with the classical size effect. Near the maximum at temperatures below 0.8 K, manifestations of reproducible magneto-oscillations of the resistance, which are periodic in field, have been detected. The period of these oscillations is close to a value corresponding to the passage of the flux quantum hc/e through the section of a nanowire. The Fourier analysis also confirms that the oscillations are periodic. This result is similar to the manifestation the Aharonov–Bohm effect caused by conducting surface states of Dirac fermions occupying L-valleys of bismuth.     

Resonance ionization spectroscopy of bismuth at the IGISOL facility

A programme of research has commenced at the IGISOL facility, Jyväskylä, combining the technique of resonance ionization spectroscopy with the development of the highly selective laser ion source trap (LIST). The first element of interest is bismuth, which contains three isomers of multi-quasiparticle states in near-spherical nuclei, namely ²⁰⁷Bi (21/2⁺, 182 μs), ²⁰⁴Bi (10^?, 13 ms) and ²⁰⁴Bi (17⁺, 1.07 ms). A measurement of the optical isomer shift provides a direct comparison of the mean?square charge radii between the isomer and the nuclear ground state. Due to the short isomer lifetimes the spectroscopy will be done either within the ion guide or in a sextupole ion beam guide (SPIG), located after the ion guide and used in the development of the LIST. A mixed dye-Ti:Sapphire laser ionization scheme has been successfully tested for bismuth and first off-line results have been obtained.     

Prolate deformation in the 187,189Bi isotopes

Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes ^{187, 189}Bi has been performed using the recoil decay tagging method. A rotational band has been observed in ¹⁸⁹Bi and is interpreted as a complete decoupling of a single proton from the deformed lead core. The results for ¹⁸⁷Bi suggest a similar structure and coupling scheme. This study gives the first evidence for a prolate band in a light bismuth nucleus and confirms the prolate character of the low-lying rotational band observed in the core nuclei ¹⁸⁸Pb and ¹⁸⁶Pb.Received: 21 July 2004, Published online: 21 September 2004PACS: 23.20.Lv transitions and level energies - 27.70. + q K. Hauschild: Present address: CSNSM, Orsay, France.P. Nieminen: Present address: ANU, Canberra, Australia.M. Rejmund: Present address: GANIL, Caen, France.J. Wilson: Present address: LPSC, Grenoble, France.A.N. Andreyev: Present address: TRIUMF, Vancouver, Canada.F. Becker: Present address: GSI, Darmstadt, Germany.M. Muikku: Present address: RNSA, Helsinki, Finland.     

Raman spectroscopic investigation on femtosecond laser induced residual stress and element distribution in bismuth germanate glasses

Localized microstructure and elemental redistribution were induced in bismuth germanate glasses by irradiation with high repetition rate 800 nm femtosecond laser pulses. The confocal Raman spectra were examined to study the redistribution of elements and residual thermal stress. The microscopic Raman spectra indicated that the residual thermal stress increases from the unmodified region to the center of the laser modified region, while Bi is enriched at the boundary area of the inner structure of the laser modified region relative to Ge. Electron microprobe analysis further confirmed the elemental redistribution of Bi and Ge, which agrees well with the Raman spectral analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation of Bi:TiO2 thin films by an hybrid deposition configuration: pulsed laser deposition and thermal evaporation

The aim of this work was to report the application of an hybrid deposition configuration to deposit Titanium dioxide (TiO₂) thin films modified with different amounts of bismuth (Bi:TiO₂). The samples were synthesized combining a TiO₂ laser ablation plasma with a flux of vapor of bismuth produced by thermal evaporation. By varying the deposition rate of Bi it was possible to control the amount of Bi incorporated in the film and consequently the film properties. A detailed compositional, structural, and optical characterization by XPS, RBS, Raman spectroscopy, and UV–Vis spectrometry techniques is discussed. Photocatalytic response of the deposited thin films was studied through the degradation of a malachite green solution.     

FIR NH3 cascade laser excited by a Q-switch laser

Short FIR laser pulses of high repetition rate are obtained by pumping NH₃ with the pulses of a passively Q-switched IR laser. The two cascade laser transitions observed show coupled relaxation oscillations. The pulse shapes and delay times are qualitatively in agreement with a four-level rate-equation model.Partially supported by Deutsche ForschungsgemeinschaftOn leave from Korea Standards Research Institute, Dae Deog Dan Ji, P.O. Box 3, Choong Nam, Korea, supported by Korea Science and Engineering Foundation     

Estimation of the Fulfillment of the Local Thermodynamic Equilibrium Criterion for the Plasma Generated by Laser Pulses of Various Shapes at the Surface of a Solid Target

The results of experimental estimation of the fulfillment of the local thermodynamic equilibrium (LTE) criterion for the plasma generated by laser pulses of various duration at the surface of a solid target placed in a gaseous atmosphere at standard pressure are given in the present paper. The fulfillment of all the LTE criteria is demonstrated for an ensemble of neutral atoms contained in the plasma generated by a giant laser pulse or by a laser pulse whose complex shape represents several giant pulses against the background of free-running laser oscillations. The plasma excited by the radiation of a Nd : YAG laser with energy 0.4 J per pulse is examined. We have recorded a resonance broadening of atomic Al and Mg lines. This has allowed us to estimate the density of neutral atoms contained in a plasma plume.