水汽分子对CO_2谱线加宽的影响

报道了以高分辨力连续可调谐中红外差频激光为探测光源,结合可调长光程怀特池,利用直接吸收的方法探测了CO2的10011←10002带R支以及部分P支在室温下的水汽加宽吸收光谱。在2422cm-1到2457cm-1范围内共有26条吸收谱线被探测到,采用Voigt线型对吸收谱线进行拟合,得到了CO2光谱的水汽加宽系数,结果显示CO2的水汽加宽系数平均比干燥空气的加宽系数大52%。利用实验测得的CO2的水汽加宽系数与HITRAN04数据库中CO2谱线的线位置、线强和干燥的空气加宽系数进行比较,分析了在实际大气中(海平面,10km光程)不存在水汽和存在水汽(含有2.0kPa水汽)时该波段CO2的大气透过率,结果表明潮湿空气与干燥空气之间的最大透过率差约为0.5‰。     

Tunable diode laser absorption measurement of oxygen A-band line strengths

Line strength measurements and pressure-broadening coefficients for the oxygen A-band (b¹Σ_g ⁺ X³Σ_g ^-) at 13122 cm^-1 using tunable diode laser absorption spectroscopy are reported. Diode lasers are scanned over individual lines and the absorption at different pressures is recorded; from these data the line strength for each transition is obtained. Average values for each transition are compared to those previously published, and in particular a comparison with the HITRAN database is presented. Line strengths reported here are 5–10% lower than the HITRAN values. PACS 33.20.-t; 33.70.Fd     

Neutral meson production at high p<Subscript>T</Subscript> with the PHENIX experiment at RHIC

Over the first five years of operation the PHENIX experiment at RHIC has collected a wealth of data for various systems and collision energies that is providing valuable information for the understanding of the suppression pattern observed in central Au+Au collisions at . An overview on transverse-momentum (p_T) spectra of π⁰ and η in different collision energies and systems is presented.     

Frequency-stabilized cavity ring-down spectrometer for high-sensitivity measurements of water vapor concentration

We present a portable spectrometer that uses the frequency-stabilized cavity ring-down spectroscopy technique capable of high-precision measurements of trace water vapor concentration. Measuring one of the strongest rovibrational transitions in the ν₁+ν₃ water vapor combination band near ˜ν=7181.156 cm^-1, we compare spectroscopic and thermodynamic determinations of trace water vapor in N₂, and find systematic differences attributable to water vapor background effects and/or uncertainties in line intensities. We also compare the frequency-stabilized ring-down method with other cavity ring-down approaches that are based on unstabilized probe lasers and unstabilized ring-down cavities. We show that for the determination of water vapor concentration, the frequency-stabilized cavity ring-down method has the minimum measurement uncertainty of these techniques. The minimum noise-equivalent absorption coefficient of the spectrometer was 1.2×10^-10 cm^-1 Hz^-1/2, which further corresponds to a minimum detectable water vapor mole fraction equal to 0.7×10^-9 for an absorption spectrum of 10 minutes duration. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Investigation of the high-p<Subscript>T</Subscript> strange baryon anomalies at RHIC

Results from RHIC have shown that there is an enhanced baryon/meson ratio in the intermediate transverse momentum range (2<p_T<6 GeV/c) in Au+Au collisions at both  =130 and 200 GeV. This was initially demonstrated by measurements of the p̄/π^- ratio which was then extended in p_T by the Λ/K⁰ _S ratio. The data were successfully described by models utilising different hadronization mechanisms: those having recombination of quarks and others having an interplay between flow, jet quenching and incorporating baryon junction loops. The strange particle data from the first Au+Au run at  =200 GeV gave tantalising hints that the observed enhancement of baryons compared to mesons was diminished by a p_T of 6 GeV/c, but a lack of statistics in this range made a definitive statement impossible. Here we present an extended analysis of identified strange baryons and mesons in Au+Au collisions at  =200 GeV using data obtained by the STAR experiment from the 2004 running period. The increase in statistics extends the measurement of Λ hyperons out to at least 7 GeV/c and K⁰ _S mesons out to 9 GeV/c. This data allows us to place limits on the range where in-vacuum fragmentation functions are applicable and the effect of baryon dominance is reduced. We also discuss the prospects for making these measurements using multiply-strange baryons and mesons (Ω and ϕ).     

Effect of Ta<Superscript>5+</Superscript> substitution for Mn on the ground state of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>

We report the charge state modification effects at the Mn site on the ground state properties of colossal magnetoresistive manganites. Ta⁵⁺ substitution results in an appreciable increase in the lattice parameters and unit cell volume due to increased Mn³⁺ concentration. The ferromagnetic-metallic ground state modifies to a cluster glass insulator for . The reduction in the transition temperatures with increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn³⁺ concentration and enhanced local structural effects, the local electrostatic potential of the substituent seems to contribute to the unusually strong reduction of the transition temperatures of the compounds. Thermo magnetic irreversibility just below Curie temperature (T_c), non-saturation of magnetization, two distinct magnetic transitions in ac susceptibility in an appropriate static field: close to T_c and other at low temperature (the spin freezing temperature (T_g)) and non-stationary dynamics with a characteristic maximum in the magnetic viscosity close to T_g confirm a cluster glass state for . These results find additional support from a linear low temperature magnetic specific heat of x = 0.10 with a characteristic broad maximum close to T_g.     

Comparison between theoretical calculations and high-resolution measurements of pressure broadening for near-infrared water spectra

We report N₂ and air foreign pressure broadening coefficients of more than twenty rovibrational transitions of water vapor in the 935-nm spectral region, and these measurements are compared to new theoretical calculations. The data were obtained using the frequency-stabilized cavity ring-down spectroscopy method, yielding relative uncertainties for the broadening parameters in the range 0.4-2.2%. The sensitivity of measured broadening parameters to the choice of line shape functions is discussed, and systematic differences between experimentally determined collisional broadening coefficients are shown for the cases when the observed line narrowing is interpreted in terms of Dicke-narrowing or the speed-dependence of the collisional broadening and shifting. Theoretical models of pressure broadening for these transitions agree with the measurements to within 4% for most transitions with an average relative difference of 0.63%.     

Decelerated molecular beams for high-resolution spectroscopy

Ultimately, the resolution of any spectroscopic experiment is limited by the interaction time between the particles that are to be examined and the measuring device. The obtainable spectroscopic resolution in a molecular beam experiment can be considerably improved using samples of slow molecules, as produced, for example, in a Stark-decelerator. This is demonstrated here by measuring the inversion tunneling spectrum of using a pulsed molecular beam that has been decelerated to about 52 m/s. Hyperfine resolved inversion transitions in in the state (around 1.43 GHz) are induced in a microwave region, and molecules that have undergone the transition are subsequently detected using a UV-laser based ionization detection scheme. To increase the signal intensity, the decelerated molecular beam is both transversally and longitudinally focused into the laser detection region. The observed spectral width of individual hyperfine transitions in the fully resolved spectrum is about 1 kHz, and the standard deviation of the best fit is 62 Hz.Received: 7 September 2004, Published online: 23 November 2004PACS: 33.15.Pw Fine and hyperfine structure - 33.20.Bx Radio-frequency and microwave spectra - 33.40. + f Multiple resonances - 33.70.Jg Line and band widths, shapes, and shifts - 39.10. + j Atomic and molecular beam sources and techniques     

The hyperfine and isotope structure of the Cd intercombination line – revisited

Careful analysis of the intercombination 5¹S₀–5³P₁ line of the ¹¹³Cd isotope with two hfs components and was carried out. The hyperfine splitting of this line was determined to uncertainty less than 10^-3 cm^-1 using neon-perturbed Doppler limited spectra.     

Upconversion blue emission dependence on the pump mechanism for Tm<Superscript>3+</Superscript>-heavy-doped NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Upconversion blue emissions of Tm³⁺-ion-heavy-doped NaY(WO₄)₂ crystals are investigated with three different near-infrared pump mechanisms. The dependence of upconversion efficiency on the pump mechanism is analyzed from the scope of the concentration quenching effect. Three cross-relaxation processes, , , and , which influence the upconversion dominantly in the Tm³⁺-heavy-doped system, are demonstrated theoretically and experimentally. The results indicate that Yb³⁺ ions can weaken the concentration quenching effect of Tm³⁺ ions significantly so that the blue emission efficiency can be enhanced by one order of magnitude. At the same time, the wavelength of the pump source also has considerable influence on both the population of some crucial energy levels and the upconversion mechanism. Experiments show that the upconversion blue emission in Tm³⁺/Yb³⁺ co-doped NaY(WO₄)₂ crystal under 980-nm laser diode excitation is the most intensive of these three different near-infrared pump mechanisms. The conclusions are confirmed by spectra measurements and calculations of Judd–Ofelt theory and Miyakawa–Dexter theory. PACS 42.70.Hj; 78.55.-m     

Two-step laser excitation of the highly excited even-parity states of atomic mercury

We report term energies and quantum defects of highly excited even-parity states of mercury in the 83 876–84 140 cm^-1 energy range, employing a two-step laser excitation scheme via the S₀↦6s6p³P₁ inter-combination transition. Two dye lasers, pumped by a common Nd:YAG laser, were frequency doubled by BBO crystals and used to record the spectra in conjunction with a thermionic diode ion detector. Our new observations include the much extended D₂ (22 ≤n ≤52) series and a few members of the S₁ (24 ≤n ≤30) Rydberg series. Members of the D₂ Rydberg series with such a high n value are reported for the first time. The relative intensities of the D₂ and S₁ transitions (m = 4, 5 and 6) of group II-B elements excited from the P₁ inter-combination states are also discussed.     

Metal-insulator transition in the low-dimensional organic conductor (TMTSF)<Subscript>2</Subscript>FSO<Subscript>3</Subscript> probed by infrared microspectroscopy

We present measurements of the infrared response of the quasi-one-dimensional organic conductor (TMTSF)₂FSO₃ along (E ) and perpendicular (E ) to the stacking axis as a function of temperature. Above the metal-insulator transition related to the anion ordering the optical conductivity spectra show a Drude-like response. Below the transition an energy gap of about 1500 cm^-1 (185 meV) opens, leading to the corresponding charge transfer band in the optical conductivity spectra. The analysis of the infrared-active vibrations gives evidence for the long-range crystal structure modulation below the transition temperature and for the short-range order fluctuations of the lattice modulation above the transition temperature. We also report about a new infrared mode at around 710 cm-1 with a peculiar temperature behavior, which has so far not been observed in any other (TMTSF)₂X salt showing a metal-insulator transition. A qualitative model based on the coupling between the TMTSF molecule vibration and the reorientation of electrical dipole moment of the FSO₃ anion is proposed, in order to explain the anomalous behavior of this new mode.     

Detection of acetylene by electronic resonance-enhanced coherent anti-Stokes Raman scattering

We report the detection of acetylene (C₂H₂) at low concentrations by electronic resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS). Visible pump and Stokes beams are tuned into resonance with Q-branch transitions in the v₂ Raman band of acetylene. An ultraviolet probe beam is tuned into resonance with the – electronic transition of C₂H₂, resulting in significant electronic resonance enhancement of the CARS signal. The signal is found to increase significantly with rising pressure for the pressure range 0.1–8 bar at 300 K. Collisional narrowing of the spectra appears to be important at 2 bar and above. A detection limit of approximately 25 ppm at 300 K and 1 bar is achieved for our experimental conditions. The signal magnitudes and the shape of the C₂H₂ spectrum are essentially constant for UV probe wavelengths from 233.0 to 238.5 nm, thus indicating that significant resonant enhancement is achieved even without tuning the probe beam into resonance with a specific electronic resonance transition. PACS 42.65.Dr; 42.62.Fi; 42.65.-k     

Investigation of Rb <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript> atomic lines in strong magnetic fields by fluorescence from a half-wave-thick cell

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D ₁ line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D ₁ line of ⁸⁷Rb and ⁸⁵Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields.     

Sub-Doppler fluorescence on the atomic <Emphasis Type="Italic">D</Emphasis><Subscript>2</Subscript> line of a submicron rubidium-vapor layer

An extremely thin cell (ETC) with the thickness of a Rb atomic vapor layer in the range of 100–300 nm was fabricated. It is demonstrated that a simple laser-diode technique with a single resonant light beam is sufficient to observe separately all of the atomic hyperfine transitions of the D ₂ line of Rb (780 nm) and also allows us to measure the relative transition probabilities of the hyperfine transitions. The onset of collisional self-broadening of the hyperfine transitions as the number density of atoms increases was studied. The detrimental role of the atoms with slow longitudinal velocity in the sub-Doppler response of the Rb ETC is demonstrated by studies in which the cell is tilted from normal incidence of the laser beam. It is also shown that using an ETC allows us to resolve in a moderate external magnetic field the Zeeman splitting of the hyperfine transitions of the ⁸⁷Rb D ₁ transition F _g=1F _e=1,2. Received: 19 February 2003 / Revised version: 4 April 2003 / Published online: 2 June 2003 RID="*" ID="*"Corresponding author. Fax: +374/32-31172, E-mail: david@ipr.sci.am     

Hyperfine structure and isotope shifts in near-infrared transitions of atomic nitrogen

We have obtained Doppler-free spectra of transitions in the → 2p²(³P) and → multiplets of atomic nitrogen using saturated absorption spectroscopy. These multiplets consist of respectively of seven and eight transitions, and have center of gravity wavelengths of 821 nm and 869 nm. Values for the hyperfine structure coupling constants of all the upper and lower states for these multiplets were obtained for both ¹⁴N and ¹⁵N. Isotope shifts of three transitions in each multiplet were also measured, and a significant J-dependence to the shifts was observed.     

Determination of the η and η<Superscript>′</Superscript> mixing angle from the pseudoscalar transition form factors

The possible range of the η– mixing angle is determined from the transition form factors F_ηγ(Q²) and with the help of up-to-date experimental data. For this purpose, the quark-flavor mixing scheme is adopted and the pseudoscalar transition form factors are calculated in the framework of light-cone pQCD, in which the transverse-momentum corrections and the contributions beyond the leading Fock state have been carefully taken into consideration. We construct a phenomenological expression to estimate the contributions to the form factors beyond the leading Fock state, based on their asymptotic behavior at Q²→0 and . By taking the quark-flavor mixing scheme, our results lead to , where the first error comes from the experimental uncertainty and the second error from the uncertainties of the parameters of the wavefunction. The possible intrinsic charm component in η and is discussed, and our present analysis also disfavors a large intrinsic charm component in η and , e.g. . PACS 13.40.Gp; 12.38.Bx; 14.40.Aq     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

Line-shape study of water vapour by tunable diode laser spectrometer in the 822–832 nm wavelength region

A near-infrared tunable diode laser absorption spectrometer is set up to measure the air-induced broadening coefficients and the line-strength parameters of water-vapour overtone transitions within the (2,1,1)(0,0,0) band in the 822–832 nm wavelength region. A Hitachi HL8311 E double hetero-junction structure diode laser is used as a probe. The diode laser controller is home-built and stable within ±10 A and ±10 mK, respectively. The laser-head mount has a simple design and provides easy access whenever changing of the laser head is required. The diode laser emission wavelength is thermally tuned between 50 °C and 12 °C. Thermal tuning of the diode laser emission wavelength is used to reveal the mode structure of the diode laser and to probe the overtone-band transitions of water vapour within its operating wavelength range. Current tuning of the diode laser is used at a fixed laser temperature to study the transitions one at a time. A balanced detector is used to improve the S/N ratio of the spectrum. A phase sensitive detection technique is followed to obtain the first-derivative spectra of the overtone transitions. The first-derivative spectra have been recorded at different air pressures inside the sample cell while the water-vapour pressure is kept fixed. The first-derivative spectrum is numerically integrated to obtain the original line shape. The original line shape is fitted with a Voigt profile by using a nonlinear least-squares fit program to extract the air-broadening coefficient and the line-strength parameter. The data obtained in our work is compared with the results of the HITRAN database. PACS 33.70.-w; 33.70.Fd; 33.70.Jg     

Electroluminescence in SrTiO<Subscript>3</Subscript>:Cr single-crystal nonvolatile memory cells

Metal–insulator–metal (M–I–M) structures involving transition-metal oxides and, more recently, also perovskite oxides with resistive switching effects have attracted substantial interest in research aimed at nonvolatile memories of nanometer dimensions. Although some models are presently under discussion, it is still not clear whether the fundamental switching mechanism is an interface or a bulk property, or a combination of both. Extended defects, such as dislocation lines and changes in the oxygen vacancy concentration, are considered responsible for the conducting state, and local reduction/oxidation processes have been proposed to be responsible for the resistive switching. In addition, the role of dopants has not been discussed in depth. Here we report on an electric-field-controlled electron trapping/detrapping process involved in the resistive switching in Cr-doped SrTiO₃. Electroluminescence (EL) measurements reveal that during resistive switching, light emission is observed only in the switching transition from high to low conductivity. The EL spectrum is typical for Cr³⁺ in an octahedral ligand field, indicating that the switching process involves trapping/detrapping of electrons at the Cr site. With increasing conductivity of SrTiO₃, we observe a change from the predominant (R-line) to the vibronically red-shifted transition, which points to a modification of the Cr-occupied lattice sites. PACS 71.30.+h; 78.60.Fi; 73.40.Rw; 78.55.-m; 85.30.Tv