Atomic coherence effects on optically pumped cesium atoms in static magnetic field

The population difference between ground states F = 4 and F = 3 is calculated for Cs atoms pumped on the D₂ line by a resonant laser beam. The pumping efficiency for Cs atoms in a static magnetic field on two hyperfine transitions (6S_1/2 F = 4 → 6P_3/2 F′ = 3 and F′ = 4) is calculated for various pump laser intensities. The population difference as a function of the static magnetic field exhibits a dip centered at the zero magnetic field, which corresponds well with the Zeeman coherence between sublevels of the F = 4 state. The full-width at half-maximum (FWHM) of the dip as a function of the pump laser intensity shows abnormal power broadening behavior that differs for different hyperfine transitions. We present experimental results that agree with the theoretical calculations.     

Excess molar heat capacity of isobutyric acid–water binary liquid mixtures near and far away from the critical temperature

The heat capacity of the liquid–liquid mixture isobutyric acid–water has been measured for the first time near and far away from its critical point using an adiabatic calorimeter. The measurements were performed at atmospheric pressure, in the one phase region as a function of three temperatures: (1) T − T_C = 0.055 °C, (2) T − T_C = 3.055 °C, (3) T − T_C = 8.055 °C and of the composition X in acid (IA). The heat capacity C_p decreases rapidly when X increases at the used temperatures. Near the critical composition, C_p is not affected by the correlation of the concentration fluctuations.

The molar excess heat capacity of the system under investigation was analysed along the phase diagram and considered as a structural transformation effect.     

Influence of N2:(N2 + Ar) flow ratio and substrate temperature on the properties of zirconium nitride films prepared by reactive dc magnetron sputtering

Preferred crystal orientation and low electrical resistivity are required for ZrN_x films applied in electronic devices. In this paper, effects of N₂:(N₂+Ar) flow ratio (F(N₂)) and substrate temperature on the properties of the films deposited on glass substrate by reactive dc sputtering are investigated. In a wide range of F(N₂) (4–24%), the films show fcc NaCl structure. While for F(N₂) in the ranges of 5–12, 12–24 and >24%, the films show (1 1 1)/(2 0 0), (1 1 1) only and amorphous structures, respectively. The electrical resistivity increases with F(N₂) from 5 to 24%, and can be controlled to some extent by changing the substrate temperature.     

Temperature dependence of the specific heat of anisaldazine close to phase transitions

The experimental data for the specific heat C_p is analyzed at various temperatures close to the nematic–isotropic liquid (T_NI = 180.5 °C) and the solid–nematic (T_SN = 168.9 °C) transitions in anisaldazine.

Values of the critical exponent for the specific heat, which describe a λ-transition between nematic and the isotropic liquid, and a jump discontinuity between solid and nematic phases, are deduced for anisaldazine. They are compared with the model predictions.     

Crosstalk between two-photon and two-color (two-photon) excitation in optical beam induced current generation with two confocal excitation beams

We analyze the influence of residual two-photon excitation (2PE) in two-color (two-photon) optical beam induced current (2CE-OBIC) generation in wide band gap semiconductor samples. 2CE-OBIC generation is accomplished with two confocal excitation beams of separation angle θ and wavelengths λ₁ and λ₂ where , λ_e = hc/E_b, h is the Planck’s constant, c is speed of light in vacuum, and E_b is the energy band gap. Because the conduction band of the sample is a continuum, at least one excitation beam would also contribute an undesirable 2PE-OBIC signal that degrades the signal-to-noise ratio of the measured 2CE-OBIC response and broadens the effective OBIC distribution in the sample particularly when θ ≠ 0 or π. We show that the deleterious effects of crosstalk are reduced by a careful selection of λ₁ and λ₂ and the relative excitation beam intensities. λ₁ and λ₂ should be chosen to minimize the ratio of the two-photon absorption coefficients (β₁, β₂) to the 2CE absorption coefficient β₁₂ or at least satisfy the constraint: β₁ + β₂  β₁₂. Keeping the two excitation intensities equal is beneficial only when β₁ = β₂. Otherwise, it is advantageous to bias the intensity ratio towards the wavelength with a lower 2PE absorption coefficient.     

Superconducting properties of ZnO-doped (Bi, Pb)-2223 thick film on Ni and NiO substrates prepared by spray deposition technique

The superconductivity of ZnO-doped (Bi, Pb)-2223 thick film on the Ni and NiO substrates, which was prepared by the spray deposition technique with cold forging, was investigated by characterizing the critical current density (J_c), the critical temperature (T_c), the orientation factor (f), and the microstructure of the film. The thickness of the thick film prepared by the spray deposition method was approximately 10 μm. The maximum J_c value of (Bi, Pb)-2223 film on NiO substrate was approximately 2200 A/cm² (I_c = 110 mA) when the film was sintered at 865 °C for 1 h with a cooling rate of 0.5 °C/min from 865 °C to 650 °C; in the case of Ni substrate, a maximum J_c value of approximately 2000 A/cm² (I_c = 100 mA) was obtained for the (Bi, Pb)-2223 thick film when a cooling rate was 3 °C/min. Such a difference in the J_c values of (Bi, Pb)-2223 thick film on Ni and NiO substrates is attributed to the presence of reaction layer at the (Bi, Pb)-2223 and substrate interface. In addition, the variations in the orientation factor of (Bi, Pb)-2223 thick film on NiO substrate related to those of J_c values. The J_c values of (Bi, Pb)-2223 film on NiO substrate with ZnO doping extremely depended on the amount of ZnO doping and the 0.5 wt% ZnO-doped (Bi, Pb)-2223 thick film deposited on NiO substrate, which was sintered at 835 °C for 1 h in air with a cooling rate of 1 °C/min, showed a J_c value of approximately 1200 A/cm² (I_c = 60 mA). Thus, it is considered that a small amount of ZnO doping was effective in lowering the sintering temperature of (Bi, Pb)-2223 thick film, resulting the improvement in the intragranular weak bonding or Josephson junction.     

Gas source MBE grown wavelength extended 2.2 and 2.5 μm InGaAs PIN photodetectors

Using homo-junction structure and relative thin linear graded In_xGa_1−xAs as the buffer layer, extended wavelength InGaAs PIN photodetectors with cut-off wavelength of 2.2 and 2.5 μm at room temperature have been grown by using GSMBE, and their performance over a wide temperature range have been extensively investigated. For those 2.2 or 2.5 μm detectors with 100 μm diameter, the typical dark current (V_R = 10 mV) and R₀A are 57 nA/10.3 Ω cm² or 67 nA/12.7 Ω cm² at 290 K, and 84 pA/4.70 kΩ cm² or 161 pA/3.12 kΩ cm² at 210 K respectively. The thermal activation energies of the dark current are 0.447 eV or 0.404 eV for 2.2 or 2.5 μm detectors respectively.     

Superconductivity and pseudogap states studied by microwave conductivity measurements of λ-(BEDT-TSF)2GaCl4

We have investigated the microwave response at 45 GHz in an organic superconductor λ-(BEDT-TSF)₂GaCl₄ with T_c = 4.8 K. We determine the μ₀H_c2–T phase diagram from microwave loss and find that the superconducting state is in the pure limit (l/ξ_GL  10). Although the real part of the complex conductivity (=σ₁ + iσ₂) does not show a coherence peak just below T_c, the London penetration depth completely saturates at low temperatures down to T/T_c = 0.2, which may provide an evidence for a conventional s-wave pairing. In the metallic state below about 50 K, (parallel to the c-axis) deviates downward from , while σ₂, which should be zero in a conventional metal, increases exponentially toward T_c. In spite of the fact that the Hagen–Rubens limit is well satisfied as far as the dc conductivity is concerned, a Drude model is unable to explain the large positive σ₂. In order to explain such anomalies in the metallic state, we propose a possible existence of so-called a pseudogap near a Fermi level. The anomalous increase of the positive σ₂ may be attributed to an appearance of pre-formed electron pairs in the pseudogap state. This appearance can be regarded as a precursor to the superconducting transition. Such a precursory phenomenon has been observed also in the isostructural FeCl₄ salt with the anomalous metallic states, which shows a negative σ₂ in contrast to the GaCl₄ salt. Just the opposite of ground states in between the GaCl₄ and FeCl₄ salts may result in the contrasting anomalous metallic states with different precursory phenomena with opposite signs of σ₂.     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Effect of the dielectric background on dispersion characteristics of metallo-dielectric photonic crystals

We theoretically study the effect of the dielectric background in two-dimensional metallo-dielectric photonic crystals. The metallo-dielectric photonic crystal consists of a square lattice of circular metallic rods embedded into a dielectric background. We calculate the photonic band structure by means of the plane wave method and the frequency-dependent finite-difference time-domain method. The transfer matrix method is used to obtain the reflectivity characteristics. Results show that the band structures shift toward lower frequencies and become flatter when the background dielectric constant increases. In addition, degeneracy can be broken and new gaps can be created in function of the dielectric background. We also found that the relative band gap width Δω/ω_g grows with increasing background dielectric constant and widths as large as 42.3% and 13.8% for the second and third band gaps can be achieved for ε_b = 9. We have investigated the origin of the new gap in these structures by studying the electric-field distribution at the band edges for the first five modes.     

Predictions of the modified Biot-Attenborough model for the dependence of phase velocity on porosity in cancellous bone

The modified Biot–Attenborough (MBA) model for acoustic wave propagation in porous media has been found useful to predict wave properties in cancellous bone. The present study is aimed at applying the MBA model to predict the dependence of phase velocity on porosity in cancellous bone. The MBA model predicts a phase velocity that decreases nonlinearly with porosity. The optimum values for input parameters of the MBA model, such as compressional speed c_m of solid bone and phase velocity parameter s₂, were determined by comparing the predictions with previously published measurements in human calcaneus and bovine cancellous bone. The value of the phase velocity parameter s₂ = 1.23 was obtained by curve fitting to the experimental data for 53 human calcaneus samples only, assuming a compressional speed c_m = 2500 m/s of solid bone. The root-mean-square error (RMSE) of the curve fit was 15.3 m/s. The optimized value of s₂ for all 75 cancellous bone samples including 22 bovine samples was 1.42 with a value of 55 m/s for the RMSE of the curve fit. The latter fit was obtained by using of a value of c_m = 3200 m/s. Although the MBA model relies on the empirical parameters determined from experimental data, it is expected that the model can be usefully employed as a practical tool in the field of clinical ultrasonic bone assessment.     

Gas Cotton-Mouton constant measurement by extrapolation in dissolved binary liquid solutions

The magneto-optic Cotton-Mouton effect constant C, light refraction index n and density ρ of binary solutions of toluene in carbon tetrachloride, -picoline and β-picoline in 1,4-dioxane have been measured at different concentrations. The results have been used for the calculation of the molar C^M constants of the solutions. By extrapolating the values C^M = C^M(f₂) for the concentration f₂ → 0, the constant _∞C₂^M = _gasC₂^M of the dipolar component of the solution has been found, which is interpreted as the Cotton-Mouton gas constant. For all solutions, the reduction factors of the dissolved component have been calculated and their linear dependence on the solution concentration has been found.     

A spectroscopic ellipsometric investigation of new critical points of Zn1−xMnxS epilayers

Zn_1−xMn_xS epilayers were grown on GaAs (1 0 0) substrates by hot-wall epitaxy. X-ray diffraction (XRD) patterns revealed that all the epilayers have a zincblende structure. The optical properties were investigated using spectroscopic ellipsometry at 300 K from 3.0 to 8.5 eV. The obtained data were analyzed for determining the critical points of pseudodielectric function spectra, (E) = ₁(E) + i₂(E), such as E₀, E₀ + Δ₀, and E₁, and three E₂ (Σ, Δ, Γ) structures at a lower Mn composition range. These critical points were determined by analytical line-shapes fitted to numerically calculated derivatives of their pseudodielectric functions. The observation of new peaks, as well as the shifting and broadening of the critical points of Zn_1−xMn_xS epilayers, were investigated as a function of Mn composition by ellipsometric measurements for the first time. The characteristics of the peaks changed with increasing Mn composition. In particular, four new peaks were observed between 4.0 and 8.0 eV for Zn_1−xMn_xS epilayers, and their characteristics were investigated in this study.     

27Al NMR study in ZrNiAl

We have studied the microscopic properties of the hexagonal ZrNiAl, a model compound for a wide family of intermetallic compounds crystallizing in this type of structure, by using ²⁷Al NMR spectroscopy. We have investigated the lineshape of static and MAS NMR spectra as a function of magnetic field strength (4.7–9.4 T) and temperature (5–300 K). Our data indicate that the ²⁷Al NMR spectra result from a combined effect of quadrupole and anisotropic shift interactions. The ²⁷Al nuclei are in an environment characterized by the quadrupole coupling constant e²qQ/h of 3.3 MHz, asymmetry parameter η_Q of 0.42, isotropic shift δ_iso of 393 ppm, shift anisotropy δ_anis = δ_zz − (δ_xx + δ_yy)/2 of 150 ppm, and asymmetry factor η_S of 0.5. They are found to be temperature independent. The spin–lattice relaxation rate measured at 7.05 T is proportional to the temperature with T₁T = 135 s K. The mechanisms responsible for observed values of δ_iso, δ_anis, T₁T, and the enhanced Korringa constant are discussed.     

Structural and optical properties of thermally evaporated Bi2Te3 films

Bi₂Te₃ films were prepared by thermal evaporation technique. X-ray diffraction analysis for as-deposited and annealed films in vacuum at 150 °C were polycrystalline with rhombohedral structure. The crystallite size is found to increase as the film thickness increases and has values in the range 67–162 nm. The optical constants (the refractive index, n, and absorption index, k) were determined using transmittance and reflectance data in the spectral range 2.5–10 μm for Bi₂Te₃ films with different thicknesses (25–99.5 nm). Both n and k are independent on the film thickness in the investigated range. It was also found that Bi₂Te₃ is a high refractive index material (n has values of 4.7–8.8 in the wavelength range 2.5–10 μm). The allowed optical transitions were found to be direct optical transitions with energy gap  eV. The optical conductivities σ₁ = ƒ(hν) and σ₂ = f(hν) show distinct peaks at about 0.13 and 0.3 eV, respectively. These two peaks can be attributed to optical interband transitions.     

环位形下鱼骨模驱动快离子输运的数值模拟研究

考虑包含动理学效应的鱼骨模结构,使用导心轨道程序 ORBIT,在磁面坐标下研究了不同的扰动模 幅度、频率对快离子再分布的影响,并分析了粒子与扰动发生共振的条件。模拟得出,鱼骨模扰动会使快离子在 实空间、相空间中发生再分布,芯部( ψ_p/ψ _w≤0.2 ,ψ_p 为极向磁通,ψ_w 为最后一个闭合磁面的磁通)快离子密 度下降约 20%,中间磁面位置上( ψ_p/ψ _w≥0.2,ψ_p/ψ _w≤ 0.6)的快离子密度增加约 7%;通过扫描频率发现,相空间中快 离子的再分布对模式频率敏感,并分析了快离子与鱼骨模扰动共振的条件。     

Chaotic signal generation and cancellation using a micro ring resonator incorporating an optical add/drop multiplexer

We propose a new design of a chaotic signal generation and cancellation system using an all fiber optic scheme. A system consists of a standard diode laser, a fiber optic micro ring resonator, and an optical add/drop multiplexer. When light from the diode laser is input into the fiber ring resonator, the chaotic signal can be generated by using the selected fiber ring resonator parameters and the diode laser input power. The required signal is obtained in the transmission link via the add/drop device by a specific user at the drop port. Simulation results obtained have shown the potential of application, especially, when the practical ring radius is 10 μm with the optical input power is in the range of the communication standard diode laser, for instance, when the coupling coefficients of the add/drop device are κ₁ = 0.01 and κ₂ = 0.01–0.9. When the add port of the add/drop device is employed, such a system can also be utilized for the multi user applications.     

Population lensing effect in Cr:LiSAF probed by Z-scan technique

An experiment has been performed for measuring a nonlinear refractive index that is due to the polarizability difference Δ_P between excited (⁴T₂) and ground (⁴A₂) states in a Cr³⁺:LiSAF crystal at λ = 647 nm. The latter one is responsible for a population lensing effect which has been monitored by using the eclipsing Z-scan technique. We have performed a data analysis that allows to distinguish between thermal and population contributions to the lensing effect. We have found Δ_P = 4.6 × 10⁻²⁵ cm³ which is in a good agreement with our previous measurements with a different technique.     

Radiative and non radiative spectroscopic properties of Er ion in tellurite glass

We have investigated in detail the mechanism of infrared emission and upconversion emission of Er³⁺ in tellurite glass as a function of the dopant concentration. Both the infrared and upconversion emissions are competing processes and the efficiency of infrared emission at 1534 nm is 100% at the lowest Er content (0.5 mol%) and reduces to 50% at higher dopant concentration (>2 mol%). The green upconversion emission at 548 nm is mainly due to the excited state absorption (ESA) from ⁴I_11/2, which populate the ⁴F_7/2 level. In addition to this, the possible energy transfer (ET) through Er³⁺(⁴I_11/2) + Er³⁺(⁴I_11/2) → Er³⁺(⁴F_7/2) + Er³⁺(⁴I_15/2) can also results in the green emission as is noticed from the concentration dependent efficiency change of the green emission. The fluorescence quenching of green emission with Er concentration may be related with the cross relaxation (CR) process ²H_11/2 + ⁴I_15/2 → ⁴I_9/2 + ⁴I_13/2. The red emission is due to the combined effect of the ESA from level ⁴I_13/2 to ⁴F_9/2, the energy transfer process described by Er³⁺(⁴I_13/2) + Er³⁺(⁴I_11/2) → Er³⁺(⁴F_9/2) + Er³⁺(⁴I_15/2) and the cross relaxation process.