A tunable diode laser system for the remote sensing of on-road vehicle emissions

2 O, and NO₂ emissions have been measured with this instrument. The system is also capable of measuring CO, NH₃, H₂CO, CH₃OH, and other small molecules in vehicle exhaust. Received: 18 May 1998/Revised version: 1 July 1998     

Phase separation and partial devitrification in soda-lime silicate glasses

2 O-rich droplets dispersed throughout the SiO₂-rich matrix and nanoparticles of metallic silver. In exchanged specimens the joint effect of colloidal silver and electric field results in partial transformation of the amorphous droplets into crystalline Na₂O particles. Received: 11 February 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

A new stable organic metal: -(BETS)C(CN). The first -type radical cation salt with a planar-triangular discrete organic anion

The -(BETS)₂C(CN)₃ radical cation salt was prepared by electrocrystallization, and its crystal structure was determined by single crystal X-ray diffraction. The electronic structure of -(BETS)₂C(CN)₃ was studied by means of the extended Hückel tight binding method. The electrical conductivity of this salt as a function of temperature shows a metallic behaviour down to 1.3 K. Shubnikov-de Haas oscillations reveal both the classical and magnetic breakdown orbits on the Fermi surface typical of the -type organic conductors. In addition, a low frequency oscillation (250 T) which is not predicted by the band structure calculations has been found in the oscillation spectrum. Received: 11 March 1998 / Revised: 9 June 1998 / Accepted: 11 June 1998     

New green self-frequency-doubling diode-pumped Nd:Ca4GdO(BO3)3 laser

3+ :Ca₄GdO(BO₃)₃ (Nd:GdCOB). 21 mW of green cw laser emission for an absorbed pump power of 820 mW were achieved under laser diode-pumping. 64 mW of green cw laser output were obtained with 1 W of absorbed pump power under titanium-sapphire pumping. Its availability in large-size crystals with good optical quality makes Nd:GdCOB a true challenger to the best SFD laser crystal reported so far: Nd:YAl₃(BO₃)₄ (Nd:YAB or NYAB). Received: 2 March 1998/Revised version: 20 May 1998     

CO2 laser-induced plasma CVD synthesis of diamond

2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron). Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H₂:CH₄ gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO₂ laser focused beam produced plasma. The deposition area was about 1 cm² and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed. Received: 15 January 1998/Accepted: 16 January 1998     

Low temperature thermodynamical properties of the organic chain conductor (TMTSF)AsF

We report on specific heat measurements of the quasi-one-dimensional organic salt (TMTSF)₂AsF₆ in its spin density wave state between 75 mK and 7 K. Similarly to (TMTSF)₂PF₆, we find discontinuities in the lattice contribution at 1.9 K an d 3.5 K ascribed to sub-spin density wave phases. Time-dependent effects due to dynamics of low-energy excitations in metastable states occur only below 0.2 K which yields an activation energy for the equilibrium energy relaxation process of 0.34 K, 4-5 times smaller than found for (TMTSF)₂PF₆. Finally the reduction of the low-energy excitations contribution to the specific heat in comparison to PF₆ reveals an intermediate cubic-like regime between 0.25 and 0.5 K that we tentatively describe as the phason contribution of the incommensurate spin density wave modulation. Received: 17 March 1998 / Revised: 27 July 1998 / Accepted: 22 September 1998     

Estimation of trap concentration in photorefractive crystals by a technique of adaptive holographic interferometry

12 GeO₂₀, Bi₁₂SiO₂₀, Bi₁₂TiO₂₀). Received: 17 June 1998/Revised version: 3 August 1998     

Flow equations and the Ruderman-Kittel-Kasuya-Yosida interaction

In the past different models for the magnetic salt vanadyl pyrophosphate (VO)₂P₂O₇ were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations. In this paper we propose a 2D model that fits better to experimental observations. Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998     

Total cross-sections for positron scattering by a series of molecules

The additivity rule is employed to obtain the total (elastic+inelastic) cross-sections for positron scattering from molecules including a number of diatomic, polyatomic molecules (H₂, N₂, HCl, CO₂, NH₃, SF₆, CH₄, C₂H₄ and C₃H₈) over an incident energy range of 10-1000 eV. The total cross-sections (TCS) of the constituent atoms of molecules are obtained by employing a complex optical model potential (composed of static, polarization and absorption potential). The present results are compared with experimental data and other theoretical calculations, good agreement is obtained in intermediate- and high-energy region. Received: 11 November 1997 / Revised: 23 March 1998 / Accepted: 16 June 1998     

V:YAG – a new passive Q-switch for diode-pumped solid-state lasers

gsa =3.0×10^-18 cm² and σ_esa=1.4×10^-19 cm² at 1064 nm, and σ_gsa=7.2×10^-18 cm² and σ_esa=7.4×10^-19 cm² at 1342 nm. Q-switched operation was demonstrated at 1064 nm and 1342 nm from a Nd:YVO₄ microchip laser, producing pulses as short as 9.3 ns at 1342 nm with peak powers of 350 W. Received: 17 March 1998/Revised version: 8 June 1998     

Charge localization in organic conductors (TM)X: The influence of anion ordering

An investigation of the different contributions leading to charge localization in a 1/2 or 1/4 filled band 1D conductor has been conducted through a study of transport properties in the solid solution [(TMTSF)_1-x (TMTTF) _x]₂ReO₄. The existence of an ordering transition of the anions allows to identify two contributions to the electronic potential with wave vector 4k_F. A dominant on-site 4k_F potential besides the bond contribution is revealed when Umklapp scattering is pertinent via the weakening of the localization arising at the (0, 1/2, 1/2) anion ordering which is stabilized under pressure in the compound [(TMTSF) _0.5 (TMTTF)_0.5]₂ReO₄ at variance with the enhancement of localization observed in the homomolecular (TMTTF)₂ReO ₄ material. Received: 13 May 1998 / Revised: 8 July 1998 / Accepted: 9 July 1998     

Long and short range spin-spin interactions in ErBaCuO

Dipolar spin-spin interactions play a crucial role as for the magnetic order in the compounds of the RBa₂Cu₃O_6+x family, (R = Dy, Er, Nd). However, inelastic neutron scattering data observed in ErBa₂Cu₃O₇ can be explained only if exchange interactions in addition to dipolar ones are taken into account. Received: 12 January 1998 / Received in final form: 26 March 1998 / Accepted: 10 April 1998     

Charge states of transition metal in “Cr, Co and Ni” doped Ln0.5Ca0.5MnO3 CMR manganites

The XAS study at Cr, Co, Ni and Mn K-edges was performed for the doped CMR manganites Ln_0.5Ca_0.5Mn_1-xB_xO₃ with Ln=La, Nd, Sm and B= Cr, Co, Ni (), on the samples that were studied previously for their ferromagnetic-metallic to antiferromagnetic-insulator transition. We observed that the formal charges of the doping elements are Ni²⁺, Co²⁺ and Cr³⁺. It is also evidenced that the average formal charge of the manganese is increased after doping, in agreement with the charge compensation keeping “O₃” stoichiometry. These results suggest that the doping elements participate directly to the band structure. Received: 9 January 1998 / Received in final form: 6 April 1998 / Accepted: 7 April 1998     

How to get access to long range states of highly excited molecules

Due to competition between ionic and covalent dissociation, the excited potential curves of the alkali dimers display long range structures, leading in some cases to secondary wells. We discuss the possibility of populating the well (with a depth of 1614.8 cm^-1, located at R _e = 30.5a ₀ ) that is present in the Na₂ potential curve and propose detection schemes. Received: 28 May 1998 / Revised: 5 August 1998 / Accepted: 24 September 1998     

Free-electron laser for infrared SEW characterization surfaces of conducting and dielectric solids and nm films on them

2 , BaF₂, MgO, LiNbO₃ were determined. The nonlinear spectroscopy applications of SEW–FEL techniques to studies of a second-harmonic generation (SHG) on crystal surfaces in the regime of counterpropagating SEWs – the frequency dependence of efficiency and the influence of a thin film deposition on a quartz surface – are described. Received: 15 May 1998/Accepted: 25 August 1998     

Dynamics of the Yb3+ to Er3+ energy transfer in LiNbO3

The energy transfer dynamics between Yb³⁺ and Er³⁺ ions in lithium niobate is investigated after ytterbium-pulsed excitation at 920 nm. The sensitisation of the LiNbO₃:Er³⁺ system with Yb³⁺ ions does not modify the lifetime of the ⁴I_13/2 erbium level (1.5-μm emission), whereas it induces a marked, concentration-dependent change in the lifetime of the ²F_5/2 (Yb³⁺) and ⁴S_3/2 (Er³⁺) multiplets (1060-nm and 550-nm emissions, respectively). The results are analysed by using the rate-equation formalism and cross-relaxation model for the energy transfer. Received: 15 October 1998 / Revised version: 24 November 1998 / Published online: 24 February 1999     

The evolution of electronic structure in lanthanide metal clusters: Threshold photoionization spectra of and

The photoionization spectra of Pr₂-Pr₂₁ and Ce₂-Ce₁₇ have been measured near threshold. The ionization potentials (IPs) of and vary discontinuously with size, but trend downward toward the work function of the bulk metals. In general, the IPs of cerium clusters display more variation than those of praseodymium clusters. The sudden discontinuities observed in the IPs of both and is akin to that displayed by clusters of transition metal atoms, suggesting that as in transition metal clusters, the rapid evolution in geometric structure with size is the source of these discontinuities. Received: 2 January 1998 / Accepted: 10 March 1998     

Excited state absorption and stimulated emission of Nd3+ in crystals. Part 2: YVO4, GdVO4, and Sr5(PO4)3F

3+ ion in the crystals YVO₄, GdVO₄, and Sr₅(PO₄)₃F. The measurements were performed in the spectral region of the main laser transitions ⁴F_3/2→⁴I_9/2, ⁴F_3/2→⁴I_11/2, and ⁴F_3/2→⁴I_13/2by a continuous wave pump and probe technique. The calibrated gain and ESA spectra are presented and possible implications of ESA on the laser performance are estimated. It is shown that ESA can be a small loss factor to the laser emission near 1060 nm but does considerably diminish the effective emission cross sections near 1340 nm especially in Nd:YVO₄ and Nd:GdVO₄. Received: 29 January 1998/Revised version: 8 May 1998     

Patterning of YBa2Cu3O7-δ films using a near-field optical configuration

2 Cu₃O_7-δ films have been patterned by means of an arrangement employed in scanning near-field optical microscopy (SNOM). Standard SNOM probes were modified to achieve high transmission for direct writing by oxygen depletion in N₂ atmosphere. The written lines are about 1.5 μm wide and show a semiconductor-like resistivity behavior (δ≥0.5). The morphology of illuminated regions is about the same as that of the YBCO films. Received: 3 July 1998/Accepted: 6 July 1998     

Fundamental noise sources in a high-sensitivity two-tone frequency modulation spectrometer and detection of CO2 at 1.6 μm and 2 μm

2 , and its sensitivity is 7(2)×10^-8 in a 1-Hz bandwidth. The corresponding minimum detectable concentration of CO₂ in air has been estimated to be 1 ppm · m. This opens the possibility of a detection at ppb levels at 2 μm, where a two orders of magnitude increase in the CO₂ absorption signal is demonstrated. Received: 06 April 1998/Revised version: 02 July 1998