Torque equations for spin and orbital angular momenta of radiation fields and Faraday effect

The spin angular momentum S of light has never been linked to the Faraday rotation of light traveling in an optically active medium possessing a rotational invariance of a crystal, because there was no helicity term associated with the phase shift in the previous torque equation for S. In order to relate the change in S with time to the Faraday rotation, therefore, we derived an exact torque equation for S. As a result, a magnetic helicity term appeared in a new torque equation for S, so that one-half of the phase shift derived from the helicity term was equivalent to the Faraday rotation angle. However, the orbital angular momentum L had no relation to the Faraday rotation. It was thus clarified that the change in S with time is related to the Faraday rotation angle of light traveling in an optically active medium, owing to the appearance of the helicity term without a rotational invariance around the optical axis. It was also demonstrated theoretically that the Faraday rotation is accompanied by a torque acting on the crystal so that the total angular momentum of light and matter is conserved.     

Low energy excitations in CeNiSn

We have studied the magnetic excitation spectrum of CeNiSn at low energies both on a polycrystalline sample using time-of-flight technique and on a single crystal with a triple axis spectrometer. The energy gap in the excitation spectrum is clearly observed in the polycrystalline sample reconciling the earlier discrepancies between the two kinds of measurements. The experimental results are consistent with the occurrence of a quasielastic signal within the gap without any significant wave vector dependence and characterized by an energy scale Γ≈0.2 meV.     

Vortex penetration depth of κ-(ET)2Cu[N(CN)2]Br

The magnetic field dependence of the in-plane penetration depth λ_|(H) for single crystal κ-(ET)₂Cu[N(CN)₂]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ_| scales with a characteristic field that coincides with a shoulder in the λ_| vs. H curves. Above that field, λ_| increases sharply toward a second inflection point at that coincides with is close to the irreversibility line measured by magnetization. For fields larger than the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ_⊥ ∼ 300 μm, implying an anisotropy .     

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ_cms = 75° and θ_cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the amplitude at the resonance energy of 320 MeV is: .     

High-resolution photorefractive gratings in nematic liquid crystals sandwiched with photoconductive polymer film

Photorefractive gratings with high grating resolution were observed in the 20 μm thick low-molar-mass nematic liquid crystal (NLC) cell with a separate photoconductive (PC) poly(N-vinylcarbazole) layer. An orientational grating with a grating spacing of 1.9 μm was produced. It is believed that a space–charge field with small fringe spacing forms in the PC layer and its evanescent component penetrates into the NLC layer. The penetrated evanescent field drives the NLC to reorient, and consequently the orientational grating forms. The model indicates that the modulated field exists in several hundred nanometers near the surface, and thus the orientational grating is not full of the NLC film, which is consistent with the observed phenomena of the multiple diffractions. Besides, asymmetric two-beam coupling of 11.2% was achieved for the grating with a grating spacing of 1.9 μm, and a net gain coefficient of larger than 62 cm⁻¹ was obtained.     

Gain characteristics of 980 nm-pumped Er<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>–Pr<Superscript>3+</Superscript>-co-doped fiber

We present a numerical model of Er³⁺–Tm³⁺–Pr³⁺-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr³⁺, Tm³⁺, Er³⁺ concentrations are around 2.0×10²⁴, 3.0×10²⁴, 1.5×10²⁴ (ions/m³), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.     

Memory properties of a Ge nanocrystal MOS device fabricated by pulsed laser deposition

The charge–storage properties of Ge nanocrystal (Nc) memory devices with MOS structure have been studied. The Ge nanocrystals (Ncs) were prepared on a p-Si (100) matrix by means of pulsed laser deposition (PLD) combined with rapid annealing in the presence of Ar gas. The device is characteristic of better switching characteristics (the I _on/I _off>10⁵), low leakage current, which was attributed to the effect of Coulomb blockade preventing injection. A significant threshold-voltage shift of 0.85 V was observed when an operating voltage of 5 V was implemented on the device. The kind of hysteresis behavior in the double sweep suggests that the device has a good electrostatic control over the Ge Nc channel.     

High-performance SOA-based multiwavelength fiber lasers incorporating a novel double-pass waveguide-based MZI

In this paper, using a direct double-pass and a novel isolator-assisted double-pass waveguide-based Mach-Zehnder interferometer (MZI), high-performance SOA-based multiwavelength fiber lasers (MFL) are proposed and demonstrated experimentally. The filtering characteristics of the proposed isolator-assisted double-pass MZI are analyzed and examined theoretically in comparison with those of the single-pass and direct double-pass MZI. Using a direct double-pass waveguide-based MZI with the single-pass free spectral range (FSR) of 43 GHz, up to 115- and 104-channel simultaneous oscillations spaced at 21.5 GHz in the L-band and C-band are obtained, respectively, with a power non-uniformity of less than 3 dB and an extinction ratio of ∼30 dB. To the best of our knowledge, it is the highest lasing-channel count that has been achieved from an SOA-based MFL. To enhance the extinction ratio while maintaining the FSR, the proposed isolator-assisted double-pass MZI is then utilized in the laser cavity, and a stable 55-wavelength simultaneous oscillation spaced at 43 GHz is accordingly achieved in C-band with an extinction ratio of higher than 50 dB. Compared with the lasing linewidth of 0.058 nm with the conventional single-pass MZI, narrower linewidths of 0.038 and 0.028 nm are obtained with the isolator-assisted and direct double-pass MZI configurations, respectively. The lasers are stable with a maximum power fluctuation per channel of less than 0.8 dB during an hour’s test.     

Kinetics of nonisothermal crystallization in Sn<Subscript>10</Subscript>Sb<Subscript>20−<Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>70</Subscript> glassy semiconductors

The crystallization kinetics of Sn₁₀Sb_20−x Bi _x Se₇₀ (x=0,2,4,6,8) chalcogenide system has been studied. Crystallization studies using differential scanning calorimetry under nonisothermal conditions with different heating rates are reported. The glass transition temperature is found to increase with the increase in heating rate as well as with the addition of bismuth. The apparent activation energy for glass transition and that for crystallization have been determined using the Kissinger equation. Thermal stability and glass forming tendency have also been studied.     

Sensitive detection of ammonia and ethylene with a pulsed quantum cascade laser using intra and interpulse spectroscopic techniques

Spectroscopic concentration measurements of ammonia and ethylene were done with a pulsed, distributed feedback (DFB) quantum cascade (QC) laser centered at 970 cm⁻¹. An astigmatic Herriot cell with 150 m path length was employed, and we compare the results from experiments using inter- and intrapulse techniques, respectively. The measurements include the detection of ammonia in breath with these methodologies. In the interpulse technique, the laser was excited with short current pulses (5–10 ns), and the pulse amplitude was modulated with an external current ramp resulting in a ∼0.3 cm⁻¹ frequency scan. A standard amplitude demodulation technique was implemented for extracting the absorption line, thus avoiding the need for a fast digitizer or a gated integrator. In the intrapulse technique, a linear frequency down-chirp is used for sweeping across the absorption line. A 200 ns long current pulse was used for these measurements which resulted in a spectral window of ∼1.74 cm⁻¹ during the down-chirp. The use of a room temperature mercury-cadmium-telluride detector resulted in a completely cryogen free spectrometer. We demonstrate detection limits of ∼3 ppb for ammonia and ∼5 ppb for ethylene with less than 10 s averaging time with the intrapulse method and ∼4 ppb for ammonia and ∼7 ppb for ethylene with the interpulse technique with an integration time of ∼5 s.     

Ag–N dual-accept doping for the fabrication of p-type ZnO

P-type ZnO was realized by dual-doping with nitrogen and silver via electrostatic-enhanced ultrasonic spray pyrolysis. The structural, electrical, and optical properties were explored by XRD, Hall-effect, and optical transmission spectra. The resistivity of ZnO:(N,Ag) film was found to be 56 Ω cm⁻¹ with the high mobility of 76.1 cm²/V s. Compared with ZnO:Ag film, ZnO:(N,Ag) film exhibited a higher and more stable optical transmittance.     

Effect of Cd and Pb impurities on the optical properties of?fresh?evaporated amorphous (As2Se3)90Ge10 thin films

Transmission spectra (400–1500 nm) of thermally evaporated amorphous [(As₂Se₃)₉₀Ge₁₀]₉₅M₅ thin films have been analyzed to study the effect of impurities (M = Cd and Pb) on their optical properties. The refractive index increases with addition of metal impurities. The dispersion of refractive index has been studied using Wemple–DiDomenico single oscillator model. The optical gap has been estimated using Tauc’s extrapolation and was found to decrease with the addition of metal impurities from 1.46 to 1.36 eV (Cd) and 1.41 eV (Pb) with an uncertainty of ±0.01 eV. The change in optical properties with metal impurities has been explained on the basis of density, polarizability and bond energy of the system.     

RF-plasma assisted pulsed laser deposition of nitrogen-doped SrTiO3 thin films

Perovskite-type nitrogen substituted SrTiO₃ thin films were deposited with a one-step process by RF-plasma assisted pulsed laser deposition from a SrTiO₃ target using a N₂ plasma, while deposition with a NH₃ plasma yields films with almost no incorporated nitrogen. The deposited films exhibit a cubic perovskite-type crystal structure and reveal oriented growth on MgO(100) substrates. The unit cell parameters of the studied N-doped SrTiO₃ films range within 3.905<a<3.918 Å, which is slightly larger than for SrTiO₃ (a=3.905 Å). The nitrogen content in the deposited films varies from 0.2 to 0.7 atom%. The amount of incorporated nitrogen in the films decreases with increasing RF-power, while the N₂ flow rate does not have any pronounced influence on the N content. Nitrogen incorporation results in an increased optical absorption at 400–600 nm, which is associated with N(2p) energy states that have a higher energy level than the valence band in strontium titanate. The optical band gap energies in the studied N-doped SrTiO₃ films are at 3.2–3.3 eV, which is very similar to that of pure strontium titanate (～3.2 eV). Films deposited with NH₃ for the RF-plasma exhibit a lower degree of crystallinity and reveal almost no nitrogen incorporation into the crystal lattice.     

Molecular relaxations in mixtures of O2 with CO2 observed on?laser-induced gratings

Laser-induced gratings in mixtures of O₂ with CO₂ were formed by excitation of the O₂ molecules to the singlet state b ¹ Σ _g ⁺(v′=0). Density changes from heat release and from electrostriction, and variation of electric polarizability by excitation of molecules contribute to the grating. For modeling the relaxation of the excited O₂ molecules, a three-step process is assumed: Fast heat release with respect to the rotational states first, then medium fast electronic de-activation with excitation of vibrational states of the O₂ and CO₂ molecules, and then the final slow heat release processes. The observed temporal evolution of the diffraction efficiency of the grating agrees rather well with modeling. Average rates of the final relaxations and the value of the polarizability of the singlet state b ¹ Σ _g ⁺(v′=0) are determined in this way.     

Photoluminescence investigation on impurity behavior in Sb-doped HgCdTe

Temperature-dependent (4.2–115 K) and excitation-intensity-dependent photoluminescence measurements have been performed on Sb doped HgCdTe samples with the emphasis on the impurity behavior of Sb doped in HgCdTe. In addition to the observation of the localized exciton, D°A°, band to band and bound to free transition related luminescence structures, the Sb-doping-related acceptor level of about 30 meV above the bottom of the valence band at 4.2 K has been obtained.     

Structure and magnetostriction of RFex (1.6 ? x ? 2.0) and R(Fe1−yTiy)1.8 (y ? 0.2) alloys (RDy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 ? x ? 2.0) and R(Fe_1−yTi_y)_1.8 (y ? 0.2) alloys (RDy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 ? x ? 1.85. The second phase is a rare-earth-rich phase when x ? 1.8, and (Dy, Tb, Pr)Fe₃ phase when x ? 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y ? 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y ? 0.05, then remains almost unchanged in the range of 0.05 ? y ? 0.20. The magnetostriction of RFe_x alloys is improved when x ? 1.80 and reduced by increasing Fe content when x ? 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.     

Infrared gluon and ghost propagator exponents from lattice QCD

The compatibility of the pure power law infrared solution of QCD and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data are well described by a pure power law with an infrared exponent κ∼0.53, in the Dyson–Schwinger notation. κ is measured using a technique that suppresses finite volume effects. This value is consistent with a vanishing zero momentum gluon propagator, in agreement with the Gribov–Zwanziger confinement scenario. For the ghost propagator, the lattice data seem not to follow a pure power law, at least for the range of momenta accessed in our simulation.