Lifetime measurements in Gd II and Gd III using time-resolved laser spectroscopy

Natural radiative lifetimes of 20 levels (energy range between 29 000-35 000 cm^-1) in Gd II and 5 levels (energy range between 43 000-49 000 cm^-1) in Gd III have been measured using time-resolved laser-induced fluorescence in a laser-produced plasma. Received 17 July 2000 and Received in final form 13 October 2000     

硅、锗中氧的低温红外吸收

在6—300K下,利用红外傅里叶光谱仪研究了400—4000cm^-1间的硅、锗中氧的红外吸收。采用高分辨条件时,分辨率可达0.5cm^-1。研究了在低温下利用硅的1106cm^-1吸收峰和锗的855cm^-1吸收峰探测硅和锗氧含量的探测限和误差。若样品厚度为2cm,估计在20K下,硅中氧含量探测限～9.6×10¹⁴氧原子·cm^-3,锗中氧含量探测限～3.0×10¹⁴氧原子·cm^-3。同时,对不同生长条件下直拉锗单晶的氧含量进行了研究,并与用锂沉淀法所求得的锗中氧含量加以比较。对不同氧含量的硅样品的1106cm^-1吸收峰在6—300K的变化进行了观察和讨论。 关键词：     

A coherent light source,widely tunable down to 16 μm by stimulated Raman scattering

An infra-red emission tunable down to 16 μm is produced by a hydrogen Stokes shifted dye laser. The peak power measured at 16 μm is of ca. 50 kW in 2 ns within a one millimeter diameter beam. The corresponding light flux of the order of 5 MW cm^-2 could allow a multi-step vibrational excitation of molecules absorbing down to 16 μm. Simultaneous emissions from the laser and from the previous Stokes bands are available at: 0.76, 1.62, 2.09 μm with respective peak powers of 550, 50 and 20 MW. Spectral widths of 0.8 cm^-1 and of ca. 7 × 10^-2 cm^-1 are obtained for the dye laser and for each of the Stokes band respectively.     

Transition energies of atomic lawrencium

Transition energies of the superheavy element lawrencium, including the ionization potential, excitation energies and electron affinities, are calculated by the intermediate Hamiltonian coupled cluster method. A large basis set (37s31p26d21f16g11h6i) is used, as well as an extensive P space (6s5p4d2f1g). The outer 43 electrons are correlated. Accuracy is monitored by applying the same approach to lutetium, the lighter homologue of Lr, and comparing with experimentally known energies. QED corrections are included. The main goal is to predict excitation energies, in anticipation of planned spectroscopy of Lr. The ground state of Lr is , unlike the of Lu. Predicted Lr excitations with large transition moments in the prime range for the planned experiment, 20 000–30 000 cm^-1, are 7p→8s at 20 100 cm^-1 and 7p→7d at 28 100 cm^-1. The average absolute error of 20 excitation energies of Lu is 423 cm ^-1, and the error limits for Lr are put at 700 cm^-1. The two electron affinities measured recently for Lu are reproduced within 55 cm^-1, and a third bound state of Lu^- is predicted.     

Parametric generation of shortened,narrow-band picosecond pulses using a Yag-pump laser

Using a single path parametric system pumped by a YAG laser, shortened pulses are produced at various frequencies. Starting with a duration of the pump pulse of 21 ps at 9400 cm^?1 we achieve a duration of 4 ps between 2700 cm^?1 and 6700 cm^?1, of 8 ps between 13 500 cm^?1 and 16 100 cm^?1, and of 8 ps between 27 000 cm^?1 and 32 000 cm^?1. Typical bandwidths are 10 cm^?1 in the infrared, 4 cm^?1 in the visible, and 5 cm^?1 in the ultraviolet.     

Laser damage of silicon solar cells with different surface states

An experimental study of the damage of Si solar cells due to Q-switched ruby laser radiation has been made. Four kinds of specimen with different surface states were used in order to examine how the damage depends on the surface state: (a) chemically etched to a mirror finish, (b) mechanically polished by a 0.5 m Al₂O₃ powder, (c) chemically etched, but rough, (d) coated with SiO on the (c) surface. The threshold power densities, at which a change in the photo-current occurs, were for the specimens (a) to (d) respectively 60 MW cm^–2, 20 MW cm^–2, 30 MW cm^–2 and 9 MW cm^–2. Attenuations of the photo-current of the specimens, a, c and d were observed over the whole range of wavelength 500 to 1000 nm. For the b cell, however, increase of the photo-current was observed mainly in the short wavelength region.     

Electron and electron-phonon effects in the quasi-two-dimensional molecular conductor θ-(BETS)<Subscript>4</Subscript>HgBr<Subscript>4</Subscript>(C<Subscript>6</Subscript>H<Subscript>5</Subscript>Cl): Optical studies at 300–15 K

This paper reports on a study of the polarized reflectance and optical conductivity spectra of the quasi-two-dimensional molecular conductor θ-(BETS)₄HgBr₄(C₆H₅Cl) within the 700–6500-cm^?1 region at 300–15 K and within the 9000–40 000 cm^?1 region at 300 K performed along two principal directions in the crystal plane parallel to the conducting layers of the BETS molecules. The IR spectra obtained at 300 K follow a close-to-Drude behavior, with strong broad features (1200–1400 cm^?1) due to electron-vibrational (vibronic) coupling (VC) superposed on the high Drude background. As the temperature is lowered in the range 180–80 K, in the spectra there appears a Lorentz term with ω_t=2900 cm^?1, as well as three additional VC-induced bands in the 800–1180-cm^?1 region, which disappear as the temperature is decreased further. The results obtained indicate the existence of unstable structural distortions along the two principal directions in the crystal, which are accompanied by the formation of a commensurate charge-density wave.     

An ab initio calculation of the rotational-vibrational energies in the electronic ground state of NH2

We have calculated ab initio the three-dimensional potential-energy surface of the NH₂ molecule at 145 nuclear geometries spanning energy ranges of about 18 000 cm^-1 for the NH stretch and 12 000 cm^-1 for the bend. The ab initio configuration-interaction calculations were done using the multireference MRD-CI method. The calculated equilibrium configuration has NH bond length r _e = 1·0207 Å and bond angle α = 103·1°. The rotational-vibrational energies for ¹⁴NH₂, ¹⁴NHD and ¹⁴ND₂ were calculated variationally using the Morse-oscillator rigid-bender internal-dynamics Hamiltonian. For ¹⁴NH₂ we calculate that υ₁ = 3267 (3219) cm^-1, υ₂ = 1462 (1497) cm^-1 and υ₃ = 3283 (3301) cm^-1, where experimental values are given in parentheses.     

Raman spectroscopic investigation of pure and ytterbium‐doped rare earth silicate crystals

Raman spectroscopy was used to study the molecular structure of a series of selected rare earth (RE) silicate crystals including Y₂SiO₅ (YSO), Lu₂SiO₅ (LSO), (Lu_0.5Y_0.5)₂SiO₅ (LYSO) and their ytterbium‐doped samples. Raman spectra show resolved bands below 500 cm⁻¹ region assigned to the modes of SiO₄ and oxygen vibrations. Multiple bands indicate the nonequivalence of the RE O bonds and the lifting of the degeneracy of the RE ion vibration. Low intensity bands below 500 cm⁻¹ are an indication of impurities. The (SiO₄)⁴⁻ tetrahedra are characterized by bands near 200 cm⁻¹ which show a separation of the components of ν₄ and ν₂, in the 500–700 cm⁻¹ region which are attributed to the distorting bending vibration and in the 880–1000 cm⁻¹ region which are attributed to the symmetric and antisymmetric stretching vibrational modes. The majority of the bands in the 300–610 cm⁻¹ region of Re₂SiO₅ were found to arise from vibrations involving both Si and RE ions, indicating that there is considerable mixing of Si displacements with Si O bending modes and RE O stretching modes. The Raman spectra of RE silicate crystals were analyzed in terms of the molecular structure of the crystals, which enabled separation of the bands attributed to distinct vibrational units. Copyright © 2007 John Wiley & Sons, Ltd.     

Electronic and electronic-vibrational phenomena in the new organic conductor ϰ-(ET)2[Hg(SCN)2Cl] with a metal-insulator transition

The reflection spectra and optical conductivity spectra of the new organic conductor ϰ-(ET)₂[Hg(SCN)₂Cl] with a metal-insulator transition in the spectral regions 700–5500 and 9000–40 000 cm⁻¹ have been studied in polarized light at 300 K. A comparisonis made between the spectra obtained and the corresponding spectra of related isostructural conductors based on the ET molecule, and also the properties of the crystal structure of the investigated compounds. An electronic transition between the ET molecules of the dimer (ET) ₂ ⁺ in the spectral region 700–5500 cm⁻¹ has been identified, as have the features of the electronic-vibrational structure arising as a consequence of the interaction of this transition with the completely symmetric intramolecular vibrations of the ET molecule. It is found that the conductor with the stronger dimer interaction between the ET molecules has the higher the transition temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 1313–1319 (August 1997)     

Photoluminescence of O2 and S2 ions in synthetic sodalities

Photoluminescence spectra of oxygen-doped chloro- and bromosodalites and sulfur-doped chloro-, bromo- and iodosodalites were measured at temperatures between 4.2 and 300 °K. At 4.2 and 77 °K, the emission spectra of oxygen-doped sodalites consisted of a series of peaks in the wavelength range 400–700 nm, with an average energy separation of ∼ 1000 cm^-1. In addition, fine structure, attributed to lattice modes, was observed in each vibrational band. At 4.2 and 77 °K, the sulfur-doped samples showed a multiband spectrum in the 500–750 nm range, with an average separation of ∼ 570 cm^-1 between bands. The spectrum at 4.2 °K exhibited some asymmetry not observed at 77 °K, but no fine structure was resolved. At 300 °K weak, broad-band luminescence was observed from both oxygen- and sulfur-doped samples, with no vibrational structure evident. The results compared very favorably with those reported for oxygen- and sulfur-doped alkali halides, and by analogy the spectra were attributed to luminescence from O^-₂ and S^-₂ molecular ions.     

Fourier transform emission spectroscopy of the FΔ-XΦ system of TiF

The emission spectra of TiF have been reinvestigated in the 4200-15 000 cm⁻¹ region using the Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. TiF was formed in a microwave discharge lamp operated with 2.5 Torr of He and a trace of TiF₄ vapor, and the spectra were recorded at a resolution of 0.02 cm⁻¹. The TiF bands observed in the 12 000-14 000 cm⁻¹ region have been assigned to a new transition, F⁴Δ-X⁴Φ. Each band consists of four sub-bands assigned as, ⁴Δ_1/2-⁴Φ_3/2, ⁴Δ_3/2-⁴Φ_5/2, ⁴Δ_5/2-⁴Φ_7/2, and ⁴Δ_7/2-⁴Φ_9/2. A rotational analysis of the 0-1, 0-0, and 1-0 bands has been obtained and spectroscopic constants have been extracted.     

Radiative lifetimes of excited W II levels

Radiative lifetimes of 19 selected W II levels with energies between 36 000 cm^-1 and 55 000 cm^-1 have been measured with the time-resolved laser-induced fluorescence technique. The ions are generated in a hollow cathode discharge and stored in a linear Paul trap. Selected states are populated with tunable dye laser pulses and the subsequent fluorescence is measured by means of a 5 Gigasample transient digitizer and a fast photodetector with a risetime of 700 ps. By taking into account both the temporal profile of the laser pulses and the separately measured response function of the system, the lifetime can be determined from the full decay curve. A refined evaluation procedure, taking into account saturation effects in the signals, reduces the uncertainty in our data to around 1%. Received: 30 July 1998 / Revised: 18 August 1998     

The GaP(001) surface and the adsorption of Cs

GaP(001) cleaned by argon-ion bombardment and annealed at 500°C showed the Ga-stabilized GaP(001)(4 × 2) structure. Only treatment in 10^?5 Torr PH₃ at 500°C gave the P-stabilized GaP(001)(1 × 2) structure. The AES peak ratio $\text{P}\text{Ga}$ is 2 for the (4 × 2) and 3.5 for the (1 × 2) structure. Cs adsorbs with a sticking probability of unity up to 5 × 10¹⁴ Cs atoms cm^?2 and a lower one at higher coverages. The photoemission measured with uv light of 3660 Å showed a maximum at the coverage of 5 × 10¹⁴ atoms cm^?2. Cs adsorbs amorphously at room temperature, but heat treatment gives ordered structures, which are thought to be reconstructed GaP(001) structures induced by Cs. The LEED patterns showed the GaP(001)(1 × 2) Cs structure formed at 180°C for 10 h with a Cs coverage of 5 × 10¹⁴ atoms cm^?2, the GaP(001)(1 × 4) Cs formed at 210°C for 10 hours with a Cs coverage of 2.7 × 10¹⁴ atoms cm^?2, the GaP(001)(7 × 1) and the high temperature GaP(001)(1 × 4), the latter two with very low Cs content. Desorption measurements show three stability regions: (a) between 25–150°C for coverages greater than 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.2 eV; (b) between 180–200°C with a coverage of 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.8 eV; (c) between 210–400°C with a coverage of 2.7 × 10¹⁴ atoms cm^?2, and an activation energy of 2.5 eV.     

The rotational spectrum of chlorine nitrate (ClONO2) in the four lowest nν9 polyads

The analysis of the recently recorded 78-378 GHz broadband spectrum of ClONO₂ has been extended to cover rotational transitions in all 14 excited vibrational states up to 650 cm⁻¹ above the ground state. We report new measurements and analysis of the 2ν₉ and 3ν₉ dyads, and first assignment and analysis for the 4ν₉ and 5ν₉ triads. The polyad fits encompass a total of over 20 000 newly measured transition frequencies and spectroscopic constants are reported for 10 vibrationally excited states in each of ³⁵ClONO₂ and ³⁷ClONO₂. All polyads were fitted with a new coupling scheme between the perturbing states combining c-axis Coriolis and Fermi interactions. The scheme is validated by multiple tests of the physical significance of the derived parameters and it results in improved deviations of fits and significant reduction in the number of adjustable parameters.     

Das Schwingungsspektrum des monoklinen CaSO4·2H2O

The relations between the imaginary part of the optical dielectric tensor in molecular crystals and transitions active in absorption, derived in a preceding paper [1], are experimentally verified by investigating the vibrational spectrum of monoclinic crystals of gypsum. Reflection spectra of precisely oriented crystal sections were recorded using polarized light between 10 000 cm^?1 and 300 cm^?1 at room temperature and at about 15°K. The eigenfrequencies of polar vibrations and the direction and magnitude of transition moments in the crystal are derived from these spectra. These results definitely support the assumption, that the bands observed between 500 cm^?1 and 300 cm^?1 are caused by hindered rotations of the water molecules. The temperature dependence of the spectra of these molecules in the region of the two stretching modes indicates mixing of these states as a result of the crystalline field. Besides this, mechanisms are discussed, which lead to the decay of excited vibrational modes and thus give rise to the observed temperature dependence of the bandwidths.     

The far infrared spectrum of 14N16O2

High resolution Fourier transform spectra in the 8–200 cm^-1 spectral region have been used to analyse the pure rotation spectrum of nitrogen dioxide. In this way, the spin rotation levels of the (000) state were accurately measured for K_a up to 14 and N up to 54. Using a hamiltonian which takes the spin-rotation and the hyperfine operators explicitly into account, it has been possible to derive a complete set of molecular parameters (rotational, spin-rotation and hyperfine constants) for the (000) state of ¹⁴N¹⁶O₂ from these experimental data and from the available microwave measurements. Numerous perturbations due to the hyperfine Fermi contact operator were analysed as well as a local resonance [42 0 42, J = 41·5] ? [41 2 40, J = 41·5] due to the electron spin-rotation interaction. Finally, a synthetic spectrum of the (000) ← (000) band of ¹⁴N¹⁶O₂ including all hyperfine transitions has been computed, covering the 0–235 cm^-1 spectral region.     

Single-mode Nd:YAG laser with transverse diode pumping and multiloop self-pumped phase-conjugate cavity

A high-power compact repetitively pulsed Nd:YAG laser with transverse diode pumping and multiloop self-pumped phase-conjugate cavity is proposed. Pulse trains with an energy of 1.5 J and beam quality parameter of M ² ≤ 1.2 are generated at a divergence of 0.4 mrad and luminance of 5 × 10¹⁴ W/(cm² sr). The peak power of single-frequency pulses is greater than 15 MW at an energy of 170 mJ and a laser bandwidth of 300 MHz.     

Interaction between 193-nm pulsed laser radiation and α-alumina

The threshold power density of 15-ns laser pulses with a wavelength 193 nm is determined for basic modes of interaction between the radiation and α-alumina. As power density Q on the target varying in the range 0.001–100 MW/cm² increases, first the interaction mechanism changes from single-photon interaction to two-photon interaction at Q ≈ 0.1 MW/cm². At Q ≈ 5 MW/cm², the material sublimates and then the sublimation products ionize at Q ≈ 15 MW/cm². At Q ≈ 100 MW/cm², the material is removed from the surface at a rate of ≈ 10 nm per pulse.     

Pulsed photoconductivity in diamond upon quasi-continuous laser excitation at 222 nm at the formation of an electron–hole liquid

An order-of-magnitude enhancement of the pulsed photocurrent in a polycrystalline diamond sample synthesized by chemical vapor deposition is observed under the conditions of formation of an electron–hole liquid. Nonequilibrium charge carriers are excited by laser pulses at a wavelength of 222 nm with FWHM pulse duration of 18 ns and peak intensity above 2.5 MW/cm² upon cooling the sample to 90 K. For peak intensities of laser excitation lower than 1 MW/cm², sample cooling from 300 to 90 K leads to a decrease in pulsed photocurrent by about a factor of 5. The observed increase in pulsed photocurrent is attributed to the formation of the electron–hole liquid.