Dynamics Of Nd Research Articles

Layered lanthanide phosphonates Ln(2-qpH)(SO4)(H2O)2 (Ln = La, Ce, Pr, Nd, Sm): polymorphism and magnetic properties.

Polymorphic layered lanthanide coordination polymers provide opportunities to study the effect of intralayer and interlayer interactions on their magnetic dynamics. Herein we report a series of layered lanthanide phosphonates, namely, α-Ln(2-qpH)(SO4)(H2O)2 (Ln = Sm) (α-Ln), β-Ln(2-qpH)(SO4)(H2O)2 (Ln = Pr, Nd, Sm) (β-Ln) and γ-Ln(2-qpH)(SO4)(H2O)2 (Ln = La, Ce, Pr, Nd, Sm) (γ-Ln) (2-qpH2 = 2-quinolinephosphonic acid), which crystallize in monoclinic P21/c (α-Ln), triclinic P1̄ (β-Ln) and orthorhombic Pbca (γ-Ln) space groups, respectively. The structural differences between the β- and γ-phases lie not only in the intralayer but also in the interlayer. Within the layers, the Ln2O2 dimers are aligned parallel in the β-phase, but are non-parallel in the γ-phase. In the interlayer, there are π-π interactions between the quinoline groups in the α- and β-phases but not in the γ-phase. Magnetic studies reveal a field-induced slow relaxation of the magnetisation at low temperatures for compounds γ-Ce, β-Nd, and γ-Nd, and the impact of polymorphism on the magnetic dynamics of Nd(III) compounds is discussed.

Frequency-shifted dynamics of Nd:YVO4 laser with anisotropic and quite weak optical feedback

The dynamic response of single-mode a-cut Nd:YVO4 laser combined with linearly polarized oscillation and orthogonally polarized optical feedback is investigated. Under frequency-shifted of 2 MHz, the output laser exhibits amplitude and phase modulation with anisotropic feedback when arbitrary retarder is inserted in external cavity. Its response characteristics vary with both phase retardation and optical axis orientation of the retarder. The amplitude response coefficient (ARC) and the phase response coefficient (PRC) are introduced to describe the response characteristics. In the special case where phase retardation equal to π/2, there is the minimum value in ARC and jump in PRC. Based on the Jones matrix of birefringent external cavity and rate equations of micro-chip laser, theoretical analysis of the frequency-shifted dynamics is carried out, in which the amplitude and phase response coefficient bridge the measurement and simulation quite well. Under different feedback level, the response limit of micro-chip laser with anisotropic feedback is verified as low as 10-9 of the reinjected light.

Nonlinear absorption, SHG behavior and carrier dynamics of Nd and Pr doped GaSe single crystals

Undoped, 0.1 at% Nd and 0.1 at% Pr doped GaSe single crystals were grown by using modified Bridgman method. The nonlinear absorption (NA), second harmonic generation (SHG) and carrier dynamics of undoped, 0.1 at% Nd and 0.1 at% Pr doped GaSe single crystals have been studied by open aperture Z-scan, SHG and transmission ultrafast pump probe spectroscopy experiments, respectively. All of the studied crystals showed nonlinear absorption under 100 fs pulse duration and 1200 nm wavelength excitations. It was found that the doping of Nd3+ and Pr3+ into GaSe single crystals caused shifting of SHG signal peaks to the shorter wavelengths. However, transmission pumb-probe experiments revealed that all of the crystals showed NA signals with long lifetime under 620 nm pump and 626 nm probe excitations.

Dual-wavelength pulsed dynamics in Nd:GdVO_4 laser with Cr^4+:YAG saturable absorber: roles of pump rate and spot size

The dual-wavelength pulse dynamics at 1.06 μm and 1.34 μm were reported based on the mechanism of mixed spiking and passive Q switching. When the dynamical behaviors were classified based on the 1.34-μm spiking pulse evolutions in one pulse repetition period of 1.06-μm Q-switched pulse train, the multiple-pulse, leading one-on-one, multiple repetition period pulse, and simultaneously one-on-one dynamics were sequentially generated by increasing the pump power. When the spot size of 1.34 μm emission was varied, the dynamical pulse behaviors occurred in sequence, but the sizes of regions were changed. The experiments agreed with the numerical results.

Hydrogen Storage Thermodynamics and Dynamics of Nd–Mg–Ni-Based NdMg12-Type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous NdMg12-type NdMg11Ni + x wt% Ni (x = 100, 200) hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The gaseous hydrogen absorption and desorption properties were investigated by Sieverts apparatus and differential scanning calorimeter connected with a H2 detector. Results show that increasing Ni content significantly improves hydrogen absorption and desorption kinetics of the alloys. Furthermore, varying milling time has an obvious effect on the hydrogen storage properties of the alloys. Hydrogen absorption saturation ratio (\(R_{ 1 0}^{\text{a}}\); a ratio of the hydrogen absorption capacity in 10 min to the saturated hydrogen absorption capacity) of the alloys obtains the maximum value with varying milling time. Hydrogen desorption ratio (\(R_{ 2 0}^{\text{d}}\), a ratio of the hydrogen desorption capacity in 20 min to the saturated hydrogen absorption capacity) of the alloys always increases with extending milling time. The improved hydrogen desorption kinetics of the alloys are considered to be ascribed to the decreased hydrogen desorption activation energy caused by increasing Ni content and milling time.

Simultaneous measurements of terahertz emission and magneto-optical Kerr effect for resolving ultrafast laser-induced demagnetization dynamics

Simultaneous detection of THz emission and transient magneto-optical response is employed to study ultrafast laser-induced magnetization dynamics in multisublattice magnets NdFeCo and GdFeCo amorphous alloys with in-plane magnetic anisotropy. A satisfactory quantitative agreement between the dynamics revealed with the help of these two techniques is obtained for GdFeCo. For NdFeCo the THz emission reveals faster dynamics than the magneto-optical response. This indicates that in addition to spin dynamics of Fe ultrafast laser excitation triggers faster magnetization dynamics of Nd.

Effect of gain and loss anisotropy on polarization dynamics in Nd:YAG microchip lasers

Relaxation oscillation spectrums of orthogonally polarized modes versus the direction of pump polarization is observed. Unlike previous reports that the anti-phase relaxation peaks are compensated totally, in most cases, they can still be observed in total intensity fluctuation spectrum. An anisotropic rate equation model for orthogonally polarized states Nd:YAG microchip laser is developed to account for the experimental observations. Anisotropic gain and loss are included to explain the polarization dynamics.

Optical spectra and excited state relaxation dynamics of Nd 3+ in CaF 2 single crystal

Nd-doped CaF 2 crystal with high optical quality was obtained by a temperature gradient technique (TGT). Energies of the crystal field levels of Nd 3+ multiplets relevant to laser operation were determined based on optical spectra recorded at T = 10 K. Room temperature absorption spectra were analyzed in the framework of the Judd–Ofelt theory to calculate radiative transition rates and luminescence branching ratios for the 4F 3/2 level. The 4F 3/2 radiative lifetime was calculated to be 1295 μs whereas a monotonous decrease of the 4F 3/2 luminescence lifetime value from 1.45 ms to 0.9 ms was observed when the temperature increased from 10 K to 300 K. The stimulated emission cross-section of 1.48 × 10 −20 cm 2 at 1061 nm was determined using the Fuchtbauer–Ladenburg relation. All the results showed that Nd:CaF 2 would be a promising gain media in solid-state lasers.

A novel ultra-broadband transient spectrometer with microsecond measurement range based on a supercontinuum fiber laser

We show that the combination of a free-running 24 kHz supercontinuum fiber laser with a kHz femtosecond laser renders a sensitive and easy to implement transient spectrometer. It can directly extend the observation range of a standard broadband femtosecond spectrometer from the usual limit of a few nanoseconds to 1 millisecond and with the additional use of a chopper to seconds. The transmission signal from all supercontinuum pulses is recorded and assigned to the proper delay time by data post-processing. To demonstrate the performance of the device, the relaxation dynamics of Nd:YAG is measured.

Hopf bifurcation in parallel polarized Nd:YAG laser

Dynamics of Nd:YAG laser with intracavity KTP crystal operating in two parallel polarized modes is investigated analytically and numerically. System equilibrium points were found out and the stability of each of them was checked using Routh–Hurwitz criteria and also by calculating the eigen values of the Jacobian. It is found that the system possesses three equilibrium points for ( I j , G j ), where j = 1, 2. One of these equilibrium points undergoes Hopf bifurcation in output dynamics as the control parameter is increased. The other two remain unstable throughout the entire region of the parameter space. Our numerical analysis of the Hopf bifurcation phenomena is found to be in good agreement with the analytical results. Nature of energy transfer between the two modes is also studied numerically.

Sub-nanosecond pulse dynamics of Nd:LSB microchip laser passively Q-switched by Cr:YAG saturable absorber

The pulse dynamics of a Nd 3+:LSB microchip laser passively Q-switched by a Cr 4+:YAG saturable absorber has been investigated experimentally and theoretically. A generalized model of a passively Q-switched microchip laser has been proposed. This model takes into consideration the thermalization and recombination of the activator atoms in the laser medium, the transverse inhomogeneity of the pump and laser beams and the finite saturable absorber recovery time. Very good agreement between theory and experiment has been obtained for a wide range of pump power with all combinations of output couplers and absorbers. The thermalization times of Nd 3+ ions in LSB crystal have been estimated for the first time to the best of our knowledge: the thermalization time within the upper laser manifold is ∼0.4 to ∼0.8 ns, while within the lower laser manifold it is ∼0.2 to ∼0.5 ns.

Structure and Dynamics of ND3BF3 in the Solid and Gas Phases: A Combined NMR, Neutron Diffraction, and ab initio Study.

Structure and Dynamics of ND₃BF₃ in the Solid and Gas Phases: A Combined NMR, Neutron Diffraction, and ab initio Study.

Structure and dynamics of ND3BF3 in the solid and gas phases: a combined NMR, neutron diffraction, and Ab initio study.

The decrease in D-->A bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND(3)BF(3) by powder neutron diffraction. The B-N internuclear distance is 1.554(3) A, 0.118 A shorter than the most recent gas-phase microwave value and 0.121 A shorter than the single molecule geometry optimized (1.672 A, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D.F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen ((15)N and (14)N) and boron ((11)B and (10)B) chemical shifts should be rather insensitive to changes in r(BN) and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the (11)B and (14)N QCCs show large changes because of both effects. An analysis of the (10)B[(19)F] line shape in solid ND(3)(10)BF(3) yields a (11)B QCC of +/-0.130 MHz. This is reasonably close an earlier value of +/-0.080 MHz and the value of +/-0.050 MHz calculated for a [NH(3)BF(3)](4) cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T(1) measurements yield an activation energy for rotation of the ND(3) group in solid ND(3)BF(3) of 9.5 +/- 0.1 kJ/mol. Simulations of the temperature-dependent T(1) anisotropy gave an E(a) of 9.5 +/- 0.2 kJ/mol and a preexponential factor, A, of 3.0 +/- 0.1 x 10(12) s(-)(1). Our calculated value for a [NH(3)BF(3)](4) cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T(1) measurements.

Strain-dependent spin dynamics in Nd0.67Sr0.33MnO3 near the metal–insulator transition

We report on time-resolved pump–probe measurements of spin-dependent dynamics in strained Nd0.67Sr0.33MnO3 thin films grown on three different substrates: LaAlO3 (001), SrTiO3 (001), and NdGaO3 (110). The temperature dependence of the long-lived spin-relaxation component is represented well by a power-law decay of long-range correlations, clearly showing the transition from quasilong-range ferromagnetic order to a disordered paramagnetic phase. The “disordering” temperature, TM, where the intermediate phase of quasilong-range order appears, varies according to the creation of static-distortion waves under different strain forces.

Spectroscopic studies and dynamics of Nd 3+ ions in RbY 2Cl 7 single crystals. Part I. Analysis of site-selective excitation and emission spectra

Single crystals of Nd 3+:RbY 2Cl 7 were grown by the Bridgman–Stockbarger method. The host crystal contains two slightly inequivalent Y 3+ ions, each with an approximate C 2v site symmetry. The crystal-field energy levels of the Nd 3+ ion doped in the two slightly inequivalent sites of the host crystal have been measured by optical absorption spectroscopy as well as by laser-selective excitation and emission experiments. As many as 151 and 156 energy levels have been ascribed to the Nd(1) and Nd(2) sites, respectively. Emission transients of a number of the levels were determined. Strong fluorescence and upconversion transitions were recorded and some mechanisms involving excited state absorption and energy transfer between Nd 3+ ions were proposed as explanatory for the results of the present investigations.

Spectroscopic studies and dynamics of Nd 3+ ions in RbY 2Cl 7 single crystals. Part II. Crystal-field analysis

Crystal-field energy levels of Nd 3+ ions doped in the two slightly inequivalent sites of the RbY 2Cl 7 host crystal were assigned and fitted to the parameters of a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions. Using the one-electron crystal-field formalism 151 levels of the Nd(1) site and 156 levels of the Nd(2) site were assigned with a r.m.s. deviation of 17.5 and 15.4 cm −1 , respectively. Including correlation crystal-field terms into the semiempirical Hamiltonian we could obtain an improvement of the r.m.s. deviation for the Nd(1) and Nd(2) site up to 11.4 and 10.3 cm −1 , respectively, as well as the elimination of major discrepancies between the calculated and observed energy levels within the anomalous 2 H(2) 11/2 and 2 F(2) 5/2 multiplets.

Electron dynamics inNd1.85Ce0.15CuO4+δ:Evidence for the pseudogap state and unconventionalc-axis response

Infrared reflectance measurements were made with light polarized along the a- and c-axis of both superconducting and antiferromagnetic phases of electron doped Nd$_{1.85}$Ce$_{.15}$CuO$_{4+\delta}$. The results are compared to characteristic features of the electromagnetic response in hole doped cuprates. Within the CuO$_2$ planes the frequency dependent scattering rate, 1/$\tau(\omega)$, is depressed below $\sim$ 650 cm$^{-1}$; this behavior is a hallmark of the pseudogap state. While in several hole doped compounds the energy scales associated with the pseudogap and superconducting states are quite close, we are able to show that in Nd$_{1.85}$Ce$_{.15}$CuO$_{4+\delta}$ the two scales differ by more than one order of magnitude. Another feature of the in-plane charge response is a peak in the real part of the conductivity, $\sigma_1(\omega)$, at 50-110 cm$^{-1}$ which is in sharp contrast with the Drude-like response where $\sigma_1(\omega)$ is centered at $\omega=0$. This latter effect is similar to what is found in disordered hole doped cuprates and is discussed in the context of carrier localization. Examination of the c-axis conductivity gives evidence for an anomalously broad frequency range from which the interlayer superfluid is accumulated. Compelling evidence for the pseudogap state as well as other characteristics of the charge dynamics in Nd$_{1.85}$Ce$_{.15}$CuO$_{4+\delta}$ signal global similarities of the cuprate phase diagram with respect to electron and hole doping.

Upconversion and energy transfer dynamics in Nd 3+:KLiYF 5

A detailed study of the spectroscopy, mechanism and dynamics of orange and green luminescence that results from infrared pumping of Nd 3+:KLiYF 5 is presented. The transitions involved are determined using luminescence spectroscopy at 10 K. All orange and green luminescence emanates from the 4 G 7/2 and 4 G 5/2+ 4 G 7/2 states. The mechanism that populates upper emitting levels is determined through analysis of excitation spectra, excitation power dependence and luminescence lifetimes to be energy transfer between ions in the 4 F 3/2 metastable state. A rate-equation model determines the donor–acceptor pathways that dominate the energy transfer mechanism. Only two of four possible pathways operate, promoting acceptor ions to the 4 G 7/2 or 4 G 11/2+ 2 D 3/2+ 2 G 9/2+ 4 K 15/2 states while demoting donor ions to the 4 I 13/2 or 4 I 11/2 states respectively. These two pathways have substantially greater energy overlaps than the two possible routes that do not operate, strongly suggesting a Förster–Dexter transfer mechanism. The results are discussed in terms of their relevance to Nd 3+-doped laser gain media.

Spin dynamics in Nd 1− xSr xMnO 3 with x=0.5

Muon spin relaxation (μ +SR) spectroscopy has been applied to study spin dynamics in the manganite single crystal Nd 0.5Sr 0.5MnO 3. Critical slowing down of Mn spin fluctuations has been observed above the ferromagnetic ordering temperature T C∼251 K. The dynamic critical exponent z=2.00(12), deduced from muon spin relaxation rates above T C (nonasymptotic regime) agrees with the results of 3d dipolar ferromagnets. Root-exponential relaxation is observed above 160 K and has been attributed to muon spin relaxation in local regions containing differently sized small spin clusters.

Laser spectral dynamics of Nd^3+ in CaF_2–YF_3 crystals

A spectral and dynamic study of spontaneous and stimulated emission of Nd3+ in yttrofluorite CaF2–YF3(5%) crystals proves the existence of two main sites for the rare-earth ion in these crystals. Flash-lamp-pumped laser experiments show the existence of two laser output lines, centered at 1054 and 1063 nm, which correspond to stimulated emissions from the two resolved Nd3+ sites. The dependence of the time-resolved laser output energy and relative intensities of both lines on the pump energy suggests the existence of some kind of coupling between the two emissions produced by the stimulated-emission field itself. The ratio between the output energies at the two wavelengths was modeled as a simple rate-equation laser model that takes the stimulated-emission coupling into account.