Dynamic and static contributions to the zero-field splitting term of divalent nickel in fluosilicate crystals

Previously published electron paramagnetic resonance (EPR) data for Ni²⁺(3d⁷) in hydrated and deuterated crystals of zinc and nickel fluosilicate have been re-analyzed to separate the static and dynamic contributions to the fine-structure (or axial zero-field-splitting) term D in the spin-Hamiltonian. While the Debye parameters of ZnSiF₆·6H₂O and ZnSiF₆·6D₂O were determined in an earlier low-temperature study¹, those of the undiluted nickel crystals, for which good data between 4 and 77 K is lacking, have been estimated here by comparison of the data above 60 K with those for the corresponding zinc compounds. The numerical results indicate that the measured values of D are composed of a negative dynamical contribution produced by the rotational motions of the water ligands, together with both negative and positive static contributions produced by the water ligands, and the more distant [SiF₆]²⁻ and [Ni.6H₂O]²⁺ complexes, respectively. A point-charge calculation shows the contribution of the latter to be roughly +2.5 cm⁻¹ in NiSiF₆·6H₂O. The exceptionally large temperature variations of D in these crystals is attributed to the near-cancellation of the positive and negative static contributions, leaving the effect of the dynamical contribution dominant.     

Q-switched and mode-locked diode-pumped Nd:YAG laser with an LT-GaAs

Simultaneous Q-switching and mode-locking (QML) is accomplished in a diode-pumped Nd:YAG laser using low-temperature GaAs (LT-GaAs) as the saturable absorber, which also acts as an output coupler at the same time. The repetition rate of the Q-switched envelope increased from 25 to 40 kHz as the pump power increased from 2.2 to 6.9 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of 714 MHz. A maximum average output power of 770 mW was obtained.     

Acousto-optic mode-locker for Nd:Lasers using paratellurite

The design of an acousto-optic modulator using paratellurite requiring only low driving power is described. Because of the high figure of merit a high modulation index can be achieved. To avoid an intermediate transmission peak the modulator should not be operated in the Bragg-regime but rather in the transition regime. The time dependent transmission for this regime is calculated as a function of the material parameters. Experimentally, modulation indices up to 10 are obtained. Using such a TeO₂ mode-locker a pulsed Nd:Cr:GSGG laser delivered pulses down to 70 ps.     

Identification and characterization of forced degradation products and stability‐indicating assay for notoginsenosidefc by using UHPLC‐Q‐TOF‐MS and UHPLC‐MS/MS: Insights into stability profile and degradation pathways

Notoginsenoside Fc, a protopanaxadiol‐type saponin, shows multi‐pharmacological activities. Chemical stability evaluation plays a crucial role in drug development. In this study, the forced degradation behavior of Notoginsenoside Fc was investigated under hydrolytic and oxidative conditions. A specific ultra high performance liquid chromatography with quadrupole time‐of‐flight mass spectrometry was developed for the separation, identification, and characterization of the degradation products of Notoginsenoside Fc. Fifty potential degradation products were formed via deglycosylation, dehydration, hydration, isomerization, side‐chain cleaving, oxidation, and superoxidation. Notoginsenoside Fc was subjected to different pH solutions, temperatures, and time periods to assess its stability. A sensitive ultra high performance liquid chromatography‐tandem mass spectrometry was developed for the quantification of Notoginsenoside Fc, notoginsenoside ST‐4, notoginsenoside Ft1, and relative quantification of notoginsenoside Ft2, 20(R)‐notoginsenoside Ft2, notoginsenoside SFt3, and notoginsenoside SFt4. The assay was linear over the concentration range (R² > 0.997) with the lowest limit of quantification of 0.02 μg/mL for Notoginsenoside Fc, Notoginsenoside ST‐4, and Notoginsenoside Ft1. The intra‐day precision, inter‐day precision, and accuracy of the three analytes were within accepted levels. The degradation kinetics of Notoginsenoside Fc in pH 1 and 3 solutions fits to first‐ and second‐order kinetics, respectively. The degradation of Notoginsenoside Fc is pH‐, temperature‐, and time‐dependent.     

Comparison of Laser Performances of 5at.% Yb:Gd2xY2(1-x)SiO5 Crystals between Different Cutting Directions

We investigate the laser actions of 5at.% Yb:Gd_2xY_2(1-x)SiO₅ (Yb:GYSO; x=0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9,W. In contrast, the sample cut parallel reaches only 1.65W at 1044nm with a slope efficiency of 33.76% with absorbed pump power of 7.99W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68nm to 1084.82nm.     

Cooperativity in a spin transition ferrous polymer: Interacting domain model, thermodynamic, optical and EPR study

A new thermodynamic model is proposed in order to account for the high spin low spin conversion in metal-organic polymers. The model, based on the idea that the spin conversion occurs in interacting domains of like-spin metal ions, allows to explain most of the important features of various types of spin conversion. The sine qua non condition of the existence of spin transitions with hysteresis is obtained. In the case of very large cooperativity, the model predicts unusual behaviour of the spin conversion system due to a low-temperature metastable high spin state. Existence of such a state is interesting in the context of the light induced excited spin state trapping recently observed in some ferrous compounds. The model is applied to interpret the spin transition in polycrystalline ferrous polymer [Fe _1-y Cu _y (Htrz)₂ trz] (BF ₄) with y = 0.00, 0.01 and 0.10, detected by differential scanning calorimetry, optical reflectivity and electron paramagnetic resonance. The domain size and the interaction energy between the domains are estimated as, respectively, n = 11 and for the y = 0 compound. As the copper content is growing, n and tend to decrease, resulting in transformations of the shape of hysteresis loop which becomes less steep, narrows and shifts to lower temperatures. The electron paramagnetic resonance gives further evidence of the presence of like-spin domains. Received 27 November 1998 and Received in final form 19 April 1999     

Iron and its complexes in silicon

This article is the first in a series of two reviews on the properties of iron in silicon. It offers a comprehensive summary of the current state of understanding of fundamental physical properties of iron and its complexes in silicon. The first section of this review discusses the position of iron in the silicon lattice and the electrical properties of interstitial iron. Updated expressions for the solubility and the diffusivity of iron in silicon are presented, and possible explanations for conflicting experimental data obtained by different groups are discussed. The second section of the article considers the electrical and the structural properties of complexes of interstitial iron with shallow acceptors (boron, aluminum, indium, gallium, and thallium), shallow donors (phosphorus and arsenic) and other impurities (gold, silver, platinum, palladium, zinc, sulfur, oxygen, carbon, and hydrogen). Special attention is paid to the kinetics of iron pairing with shallow acceptors, the dissociation of these pairs, and the metastability of iron–acceptor pairs. The parameters of iron-related defects in silicon are summarized in tables that include more than 30 complexes of iron as detected by electron paramagnetic resonance (EPR) and almost 20 energy levels in the band gap associated with iron. The data presented in this review illustrate the enormous complexing activity of iron, which is attributed to the partial or complete (depending on the temperature and the conductivity type) ionization of iron as well as the high diffusivity of iron in silicon. It is shown that studies of iron in silicon require exceptional cleanliness of experimental facilities and highly reproducible diffusion and temperature ramping (quenching) procedures. Properties of iron that are not yet completely understood and need further research are outlined. Received: 14 December 1998 / Accepted: 22 February 1999 / Published online: 26 May 1999     

120 W high repetition rate Nd:YVO<Subscript>4</Subscript> MOPA laser with a Nd:YAG cavity-dumped seed laser

A master oscillator power amplifier (MOPA) system in which the output from an end-pumped Nd:YAG oscillator cavity dumped at 500 kHz is scaled up by a four-stage Nd:YVO₄ amplifier is reported. Decrease in extraction efficiency of the amplifier chain with crystals different from that in the oscillator was analyzed. With the 5.4 W seed output, 118 W of power was extracted from the amplifier chain at the pump power of 345 W, with an extraction efficiency of 34.2% and an overall optical–optical efficiency of 30.9% for the MOPA system. The beam quality factors were measured as M _x ²=1.45 and M _y ²=1.59 in two orthogonal directions, respectively.     

Passive mode-locking in diode-pumped c-cut Nd:LuVO<Subscript>4</Subscript> laser with a semiconductor saturable-absorber mirror

We demonstrated a diode-pumped passively mode-locked c-cut Nd:LuVO₄ picosecond laser with a semiconductor saturable-absorber mirror (SESAM) at a wavelength of 1067.8 nm. Due to the wide bandwidth of 0.48 nm, stable mode-locking has been generated with a duration as short as 3.7 ps, which is shorter than for the a-cut Nd:LuVO₄ laser. A maximum output power of 1.67 W was achieved to give a highest peak power of 3.47 KW at 18 W absorbed pump power.     

Nanoscale laser processing and diagnostics

The article summarizes research activities of the Laser Thermal Laboratory on pulsed nanosecond and femtosecond laser-based processing of materials and diagnostics at the nanoscale using optical-near-field processing. Both apertureless and apertured near-field probes can deliver highly confined irradiation at sufficiently high intensities to impart morphological and structural changes in materials at the nanometric level. Processing examples include nanoscale selective subtractive (ablation), additive (chemical vapor deposition), crystallization, and electric, magnetic activation. In the context of nanoscale diagnostics, optical-near-field-ablation-induced plasma emission was utilized for chemical species analysis by laser-induced breakdown spectroscopy. Furthermore, optical-near-field irradiation greatly improved sensitivity and reliability of electrical conductance atomic force microscopy enabling characterization of electron tunneling through the oxide shell on silicon nanowires. Efficient in-situ monitoring greatly benefits optical-near-field processing. Due to close proximity of the probe tip with respect to the sample under processing, frequent degradation of the probe end occurs leading to unstable processing conditions. Optical-fiber-based probes have been coupled to a dual-beam (scanning electron microscopy and focused ion beam) system in order to achieve in-situ monitoring and probe repair.