Compact QEPAS sensor for trace methane and ammonia detection in impure hydrogen

A compact two-gas sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) was developed for trace methane and ammonia quantification in impure hydrogen. The sensor is equipped with a micro-resonator to confine the sound wave and enhance QEPAS signal. The normalized noise-equivalent absorption coefficients (1σ) of 2.45×10^?8 cm^?1?W/ $\sqrt{}$ Hz and 9.1×10^?9 cm^?1?W/ $\sqrt{}$ Hz for CH₄ detection at 200 Torr and NH₃ detection at 50 Torr were demonstrated with the QEPAS sensor configuration, respectively. The influence of water vapor on the CH₄ channel was also investigated.     

Li+ transportation kinetics of FeF3 · 0.33H2O/C nanocomposite synthesized by one-step solid state method

A new cathode material for lithium ion battery FeF₃?·?0.33H₂O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g^?1 and corresponding charge capacity of 186.4 mAh g^?1. A reversible capacity of ca.157.4 mAh g^?1 at 20 mA g^?1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2?×?10^?13?~?3.6?×?10^?14 cm² s^?1 with a maximum of 1.2?×?10^?13 cm² s^?1 at 2.5 V. The method of GITT gave a result of 8.1?×?10^?14?~?1.2?×?10^?15 cm² s^?1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.     

Growth of high-quality ZnO thin films on (11\bar{2}0) a-plane sapphire substrates by plasma-assisted molecular beam epitaxy

High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al₂O₃ interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×10⁸ cm^?2 and an edge dislocation density of 3.38×10⁹ cm^?2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω?cm, an electron concentration of 6.85×10¹⁷ cm^?3, and a mobility of 76.5 cm²?V^?1?s^?1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals.     

Investigation of atmospheric {\text{O}}_{2}{\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} using open-path tunable diode laser absorption spectroscopy

A tunable diode laser absorption spectroscopy (TDLAS) device fiber coupled to a pair of 12.5 in. telescopes was used to study atmospheric propagation for open path lengths of 100–1,000 meters. More than 50 rotational lines in the molecular oxygen A-band O₂ $ {\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} $ transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3 % (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6 % (less than ±0.04 × 10¹⁸ molecules/cm³). Pressure was determined independently from the pressure-broadened Voigt lineshapes to within 10 %. A fourier transform interferometer (FTIR) was also used to observe the absorption spectra at 1 cm^?1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2 %, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging.     

Near and far infrared vibrational absorption ofH i − andD i − centres in KBr

Near infrared absorption measurements by Gross and Bron led to the suggestion that the threefold degeneracy of the localized vibration ofH _i ^? andD _i ^? centres in KI is completely lifted in KBr. Using thermal annealing procedures,H _i ^? -D _i ^? substitution and far infrared techniques we found that the lines at 794, 840, and 896 cm^?1 cannot be interpreted as a splitting of the main line. Only the 794 cm^?1 line can be correlated with the direct excitation of theH _i ^? oscillator. The absence of any splitting in this line (its halfwidth at 9 °K is only 1.5 cm^?1) indicates that also in KBrH _i ^? centres have at most only slightly perturbedT _d symmetry.     

\mathrm{CO}_{2}^{*} chemiluminescence study at low and elevated pressures

Chemiluminescence experiments have been performed to assess the state of current $\mathrm{CO}_{2}^{*}$ kinetics modeling. The difficulty with modeling $\mathrm{CO}_{2}^{*}$ lies in its broad emission spectrum, making it a challenge to isolate it from background emission of species such as CH^? and CH₂O^?. Experiments were performed in a mixture of 0.0005H₂+0.01N₂O+0.03CO+0.9595Ar in an attempt to isolate $\mathrm{CO}_{2}^{*}$ emission. Temperatures ranged from 1654 K to 2221 K at two average pressures, 1.4 and 10.4 atm. The unique time histories of the various chemiluminescence species in the unconventional mixture employed at these conditions allow for easy identification of the $\mathrm{CO}_{2}^{*}$ concentration. Two different wavelengths to capture $\mathrm{CO}_{2}^{*}$ were used; one optical filter was centered at 415 nm and the other at 458 nm. The use of these two different wavelengths was done to verify that broadband $\mathrm{CO}_{2}^{*}$ was in fact being captured, and not emission from other species such as CH^? and CH₂O^?. As a baseline for time history and peak magnitude comparison, OH^? emission was captured at 307 nm simultaneously with the two $\mathrm{CO}_{2}^{*}$ filters. The results from the two $\mathrm{CO}_{2}^{*}$ filters were consistent with each other, implying that indeed the same species (i.e., $\mathrm{CO}_{2}^{*}$ ) was being measured at both wavelengths. A first-generation kinetics model for $\mathrm{CO}_{2}^{*}$ and CH₂O^? was developed, since no comprehensively validated one exists to date. CH₂O^? and CH^? were ruled out as being present in the experiments at any measurable level, based on calculations and comparisons with the data. Agreement with the $\mathrm{CO}_{2}^{*}$ model was only fair, which necessitates future improvements for a better understanding of $\mathrm{CO}_{2}^{*}$ chemiluminescence as well as the kinetics of the ground state species.     

Investigation of third-order optical nonlinearity in KBe2BO3F2 crystal by Z-scan

The third-order optical nonlinearity of deep-ultraviolet (DUV) nonlinear optical (NLO) crystal KBe₂BO₃F₂ (KBBF) was investigated using single-beam Z-scan technique for the first time. The Z-scans were performed on a c-cut KBBF crystal and a KBBF prism-coupling device (PCD) with picosecond pulses at 355?nm. No two-photon absorption was observed in the experiment. The measured nonlinear refraction index n ₂ showed positive signs, indicating self-focusing Kerr effects. The n ₂ values were estimated to be (1.75±0.35)×10^?15?cm²/W with the c-cut sample and (1.85±0.37)×10^?15?cm²/W with the PCD, corresponding to the third-order nonlinear optical susceptibilities $\chi_{\mathrm{eff}}^{(3)}$ of (0.99±0.20)×10^?13?esu and (0.94±0.19)×10^?13?esu, respectively. The results are expected to promote the investigation of frequency conversion processes with ultra-short laser in KBBF crystal.     

Spin-spin interaction of Dy3+ ions in KY(WO4)2

The spin-spin interaction of Dy³⁺ ions in a KY(WO₄)₂ single crystal is investigated by electron paramagnetic resonance (EPR) spectroscopy at a temperature of 4.2 K and a frequency of 9.2 GHz. The EPR spectra of ion pairs located in different coordination shells are analyzed. It is revealed that the considerable contribution to the spin-spin interaction of the nearest neighbor ion pair nn is made not only by the magnetic dipole-dipole interaction but also by the isotropic exchange interaction with the parameter I _nn = (+601 ± 17) × 10^?4cm^?1. The exchange interaction in pairs of more widely spaced ions is substantially weaker: I _5n = (?38 ± 3) × 10^?4cm^?1 and I _9n = (+18 ± 4) × 10^?4cm^?1. For the other ion pairs, the magnetic dipole-dipole interaction dominates. It is found that the EPR spectra of single ions and ion pairs exhibit a superhyperfine structure associated with tungsten nuclei.     

Production and loss of N 2 + , Ne+ and Ne 2 + during the decay period of plasmas produced in neon-nitrogen mixtures

Studies of the time dependencies of the number density of N ₂ ⁺ , Ne⁺ and Ne ₂ ⁺ ions have been made during the decay period of plasmas produced in neon containing various concentrations of nitrogen molecules. Reaction rate constants were obtained for N ₂ ⁺ +N₂+Ne→N ₄ ⁺ +Ne((1.2±0.2)×10^?29 cm⁶ sec^?1) and Ne⁺+N₂→N ₂ ⁺ + Ne ((2.9±0.3) × 10^?12 cm³ sec^?1). The ambipolar diffusion coefficient of N ₂ ⁺ in neon was found to beD _a p _o =350±20 cm² sec^?1 Torr.     

A frequency-stabilized Yb:KYW femtosecond laser frequency comb and its application to low-phase-noise microwave generation

We present an optically stabilized Yb:KYW fs-laser frequency comb. We use an f–2f nonlinear interferometer to measure the carrier envelope offset frequency (f ₀) and the heterodyne beatnote between the comb and a stable CW laser at 1068 nm to detect fluctuations in the comb repetition rate ( $f_{\mathrm{rep}}$ f rep ). Both of these degrees of freedom of the comb are then controlled using phase-locked loops. As a demonstration of the frequency-stabilized comb, we generate low-phase-noise 10 GHz microwaves through detection of the pulse train on a high bandwidth photodiode. The phase noise of the resulting 10 GHz microwaves was ?99 dBc/Hz at 1 Hz and the corresponding Allen deviation was <2.6 × 10^?15 at 1 s, measured by comparison to an independently stabilized Ti:sapphire frequency comb. This room-temperature, optically based source of microwaves has close-to-carrier phase noise comparable to the very best cryogenic microwave oscillators.     

Simultaneous detection of trace gases using multiplexed tunable diode lasers and a photoacoustic cell containing a cantilever microphone

We report what we believe to be a novel demonstration of simultaneous detection of multiple trace gases by near-IR tunable diode laser photoacoustic spectroscopy using a cell containing a cantilever microphone. Simultaneous detection of carbon monoxide (CO), ethyne (C₂H₂), methane (CH₄) and combined carbon monoxide/carbon dioxide (CO+CO₂) in nitrogen-based gas mixtures was achieved by modulation frequency division multiplexing the outputs of four near-IR tunable diode lasers. Normalized noise-equivalent absorption coefficients of 3.4×10^?9, 3.6×10^?9 and 1.4×10^?9 cm^?1?W?Hz^?1/2 were obtained for the simultaneous detection of CO, C₂H₂ and CH₄ at atmospheric pressure. These corresponded to noise-equivalent detection limits of 249.6 ppmv (CO), 1.5 ppmv (C₂H₂) and 293.7 ppmv (CH₄) respectively over a measurement period of 2.6 s at the relevant laser power. The performance of the system was not influenced by the number of lasers deployed, the main source of noise arising from ambient acoustic effects. The results confirm that small-volume photoacoustic cells can be used with low optical power tunable diode lasers for rapid simultaneous detection of trace gases with high sensitivity and specificity.     

Line strength and collisional broadening coefficients of H2O at 2.7 μm for natural gas quality assurance applications

We employed tunable diode laser absorption spectroscopy to measure the line strength, the methane (CH₄), ethane (C₂H₆) and the propane (C₃H₈) broadening coefficients for the 523–422 H₂O transition at 3619.61 cm^?1. Water amount fractions generated by a stable and accurate humidity transfer standard, traceable to the SI units via the German national humidity standard, were used to calibrate the spectroscopic line strength measurements. We focus on the traceability of the measured line data to the SI and on uncertainty assessments following the guidelines of the Guide to the Expression of Uncertainty in Measurement. We determined the line strength to be (8.42 ± 0.07)×10^?20 cm^?1/(cm^?2 molecule) corresponding to a relative uncertainty of ±0.8%. To the best of our knowledge, we report the first methane, ethane and propane broadening coefficients of (8.037 ± 0.056)×10^?5 cm^?1/hPa, (9.077 ± 0.064)×10^?5 cm^?1/hPa and (10.469 ± 0.073)×10^?5 cm^?1/hPa for the 523–422 H₂O transition at 3619.61 cm^?1, respectively. The relative combined uncertainties of the stated CH₄, C₂H₆ and C₃H₈ broadening coefficients are in the ±0.7% range.     

A quantum cascade laser-based optical feedback cavity-enhanced absorption spectrometer for the simultaneous measurement of CH4 and N2O in air

Optical feedback cavity-enhanced absorption spectroscopy (OF CEAS) has been demonstrated with a thermoelectrically cooled continuous wave distributed feedback quantum cascade laser (QCL) operating at wavelengths around 7.84 μm. The QCL is coupled to an optical cavity which creates an absorption pathlength greater than 1000 m. The experimental design allows optical feedback of infra-red light, resonant within the cavity, to the QCL, which initiates self-locking at each TEM₀₀ cavity mode frequency excited. The QCL linewidth is narrowed to below the mode linewidth, greatly increasing the efficiency of injection of light into the cavity. At the frequency of each longitudinal cavity mode, the absorption coefficient of an intracavity sample is obtained from the transmission at the mode maximum, measured with a thermoelectrically cooled detector: spectral line profiles of CH₄ and N₂O in ambient air were recorded simultaneously and with a resolution of 0.01386 cm^?1. A minimum detectable absorption coefficient of 5.5×10^?8 cm^?1 was demonstrated after an averaging time of 1 s for this completely thermoelectrically cooled system. The bandwidth-normalised limit for a single cavity mode is 5.6×10^?9 cm^?1?Hz^?1/2 (1σ).     

Simultaneous detection of 14NO and 15NO using Faraday modulation spectroscopy

We describe a technique of simultaneous detection of ¹⁴NO and ¹⁵NO by means of Faraday Modulation Spectroscopy (FAMOS) based on a cw distributed feedback quantum cascade laser (QCL) operating near 5.4 μm. FAMOS is a spectroscopic method for selective, sensitive, and time-resolved detection of free radical molecules such as NO, in the mid-infrared spectral region. The selected spectral lines are the Q (1.5) for ¹⁵NO located at 1842.76 cm^?1 and the P (9.5) for ¹⁴NO located at 1842.93 cm^?1. The detection limit (1σ) of 6 ppb $/\sqrt{\mathrm{Hz}}$ for ¹⁵NO and 62 ppb $/\sqrt{\mathrm{Hz}}$ for ¹⁴NO has been achieved. The simultaneous detection was performed using a fast laser frequency switching between the two isotopologues with a time resolution of 2 s. The isotope ratio (δ ¹⁵N) has been determined with a precision (1σ) of 0.52‰ at 800-s averaging time for 100 ppm NO-gas with a time resolution of 2 s. δ ¹⁵N is determined after NO release from nitrite by chemical reduction with potassium iodine.     

Recent Results at BESIII

The BESIII detector operating at the BEPCII e ⁺ e ^? collider collected 2.25 × 10⁸ J/ψ events, 1.06 × 10⁸ ψ(3686) events, 2.9 fb^?1 data at ${\sqrt s}$ = 3.773 GeV and 477 pb^?1 data at ${\sqrt s}$ = 4.01 GeV, respectively, by the end of 2011. We report some recent results on light hadron spectroscopy, charmonium spectroscopy and charm physics, which are obtained by analyses of these data.     

Part II: Effect of high energy proton beam fluence on the electrical studies of lithium gallium phosphate glass electrolyte doped with selenium ions

A series of glass samples, according to the formula (100 ? x) (0.5Li₂O ? 0.2Ga₂O₃ ? 0.3P₂O₅) + xSeO₂ (x?=?0, 2, 4, 6, 8, 10) and 12 mol.%, labeled as LGPS _x (x is the mole percent of SeO₂), were synthesized through melt quenching technique. All the LGPS _x samples were irradiated by a high energy proton (H⁺) beam of 3 MeV at fluence of 10¹⁴, 5 × 10¹⁴, and 10 × 10¹⁴ ions/cm². FTIR and Raman spectra indicated that SeO₂ acts either as a glass modifier (SeO ₃ ^2? ) or a glass former (SeO ₄ ^2? ), as the dose rate of beam fluence changes. The bulk conductivity of the highest conducting sample LGPS₁₀ irradiated at a beam fluence of 5 × 10¹⁴ ions/cm² was determined as 5.87 × 10^?04 S/cm at 303 K. The super curve in the normalized spectra of electrical modulus at different temperatures confirms that the LGPS samples follow the temperature-independent, frequency-dependent relaxation time before and after irradiation.     

Optimization of perpendicular magnetic anisotropy tips for high resolution magnetic force microscopy by micromagnetic simulations

Magnetic Force Microscopy (MFM) tip coated with perpendicular magnetic anisotropy film (PMA tip) is one of the choices for high resolution imaging at low scan height (SH), since it has negligible tip–sample interaction related to its stable magnetic state, sharp, and small tip stray field. In this work, detailed micromagnetic studies are carried out to understand the effect of geometrical and magnetic parameters including the cone angle θ of the PMA tip, intergrain exchange constant $A_{2}^{*}$ , saturation magnetization M _s and uniaxial crystalline anisotropy constant K ₁ of the tip coating on the MFM tip resolution. To evaluate the resolution performance of the optimized PMA tip, MFM images of high-density granular recording media and patterned media are simulated. We find that, for the PMA tip and its coating, a cone angle in a range of 36.9^° to 53.1^°, a saturation M _s of 700 emu/cm³, a large uniaxial crystalline anisotropy constant K ₁ (>4.9×10⁶ erg/cm³) and a high intergrain exchange constant $A_{2}^{*}$ of (0.3–1.0)×10^?6 erg/cm are optimized conditions for high resolution imaging. The optimized PMA tip has an excellent performance on imaging of high-density thin film media (bit size of 8×16 nm²) at low SH of 2–8 nm and bit pattern media with a pitch of 50 nm, edge-edge spacing of 5–15 nm at SH of 8–15 nm.     

Electron paramagnetic resonance and spinlattice relaxation of Cu2+ ions in ZnSeO4·6H2O

In this paper, we present detailed studies of the EPR spectra of Cu²⁺ ions in single crystals of ZnSeO₄·6H₂O. We describe the spectrum with a rhombic spin Hamiltonian with the following parameters: g_z=2.427; g_y=2.095; g_x=2.097; A _z ⁶⁵ =138.4·10^?4 cm^?1; A _x ⁶⁵ =22.3·10^?4 cm^?1. We studied spin-lattice relaxation in the temperature range 4–300 K at the frequency v≈9.3 GHz. The measured spin-lattice relaxation rate for the orientation H∥L₄ is described well at T<5 K by a linear dependence, while at T>5 K it is described by the sum of three exponentials: $$T_1^{ - 1} = 0.27T + 3.3 \cdot 10^{\text{s}} \exp \left( {\frac{{ - 69.5}}{T}} \right) + 2.6 \cdot 10^7 \exp \left( {\frac{{ - 140}}{T}} \right) + 1.36 \cdot 10^{10} \exp \left( {\frac{{ - 735.6}}{T}} \right){\text{ sec}}^{{\text{ - 1}}} $$ .We discuss possible reasons for the exponential dependence of T ₁ ^?1 for the Raman process.     

Origin of dielectric relaxations in KHSeO4 above room temperature

The dispersion curves of the dielectric response for KHSeO₄ were obtained in the radio frequency range at several isotherms below the fast proton conducting phase (T?<?415 K). The results reveal a distinct dielectric relaxation at low frequency, which is about 682 Hz at 320 K, and then, it shifts to higher frequencies (～10 kHz) as the temperature increases. The f _max vs. reciprocal T shows an activated relaxation process with an activation energy of 0.5 eV, which is in close agreement with that associated with transport of charge carriers. We suggest that the observed dielectric relaxation could be attributed to polarization induced by the proton jump and selenate tetrahedral reorientations. The displacement of mobile H⁺ proton accompanied by SeO ₄ ^??2 tetrahedra reorientations creates structural distortion in both sublattices which induce localized dipoles like HSeO ₄ ^? .     

Feasibility of a low-voltage discharge in pure molecular hydrogen

The feasibility of initiating a low-voltage discharge in pure (free of readily ionizable impurity) molecular hydrogen is studied theoretically. A discharge with cathode fall φ₁ = 10 V, interelectrode gap L = 2 cm, and total hydrogen concentration \(N_{H_2 }^{(0)} = 2 \times 10^{15}\) cm^?3 is considered by way of example. The plasma parameters, including concentration \(N_{H^ - }\) of negative hydrogen ions H^?, are calculated. The concentration of H^? ions is maximal in the near-anode plasma and may reach \(\left( {N_{H^ - } } \right)_{\max } = 0.5 \times 10^{12}\) cm^?3. Concentration \(N_{H^ - }\) can be increased severalfold by introducing a small amount of cesium into the discharge, \(N_{Cs}^{(0)} \leqslant 10^{13}\) cm^?3. Cesium ionizes completely and concentrates in narrow near-electrode layers, which are depleted with the plasma in the purely hydrogen discharge. The discharge modifications studied in this work may be of interest as low-voltage volume plasma sources of H^? ions under conditions when a high concentration of cesium in the source plasma is undesirable.