Compact,continuous-wave,singly resonant optical parametric oscillator based on periodically poled RbTiOAsO4 in a Nd:YVO4 laser

We describe a compact all-solid-state continuous-wave, singly resonant optical parametric oscillator (SRO) based on periodically poled RbTiOAsO4. The SRO is pumped at 1.064 microm by a Nd:YVO4 laser, which is itself pumped by a 3-W diode laser. Using the intracavity technique produced an oscillation threshold for the SRO of only 1.6 W (diode-laser power). For 3 W of diode pump power some 65 mW was obtained in the (nonresonant) idler (wavelength 3.52 microm). Temperature tuning over the range 10-100 degrees C resulted in tuning ranges of 1.52-1.54 and 3.41-3.54 microm for the signal and the idler waves, respectively. Importantly, relaxation oscillations were absent.     

Novel heterocyclic systems. Part 27. The synthesis of various diazathianthrenes and the discrimination of isomeric structures using 13C-NMR and lanthanide induced shift data

Syntheses of the previously unknown 1,7-1,8- and 1,9-diazathianthrenes are reported. The former two systems were prepared via the condensation of the dianion of 2,3-dimercaptopyridine with 3-chloro-4-nitropyridine 1-oxide while the latter employed 2-chloro-3-nitropyridine. The preparation of the 1,9-diazathianthrene also led to the formation of the previously reported 1,6-diazathianthrene as a by-product in a 22% yield. The new ring systems were characterized by a combination of ¹³C nmr and ¹H lanthanide-induced shifts using Eu(fod)₃.     

A practical implementation of spectral methods resistant to the generation of spurious eigenvalues

This work describes a practical way of constructing a spectral representation of linear boundary value problems (BVPs) using a tau method. All BVPs are treated as first-order systems, unlike most implementations which tend to view the problem in terms of a single high-order differential equation. For most applications this formulation will adhere more closely to the natural derivation of the original equations from, for example, a series of conservation laws. The technique is exemplified for Chebyshev polynomials in a variety of real applications, although detailed results are provided for any polynomial basis.     

Exchange reactions of organomercury compounds

Spectroscopic studies (PMR and UV) have been carried out on mixtures of symmetrical organomercury compounds at room temperature in DMSO, pyridine, and ethanol as solvents. It has been shown that for a range of diarylmercurials, Ar₂Hg, and di-(acetaldehyde)mercury, Hg(CH₂CHO)₂, an exchange reaction occurs with the formation in solution of the unsymmetrical compound ArHgCH₂CHO. Facile exchange also occurs between pairs of diarylmercurials. A mechanism involving a four centre transition state is proposed. Simple dialkylmercurials do not undergo this exchange under mild conditions.     

Temperature waves in a rigid heat conductor

The propagation of acceleration-temperature waves in a rigid heat conductor is investigated. The theory employed allows temperature to travel with a finite wavespeed, and the full nonlinear theory is analysed. It is shown that various types of behaviour are possible for the amplitude of the wave, including one for which the amplitude becomes infinite in a finite time. Higher order temperature waves are also briefly discussed.

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Zusammenfassung Es wird die Fortpflanzung von Temperaturbeschleunigungswellen in einem starren Wärmeleiter untersucht. Die verwendete Theorie erlaubt endliche Wellengeschwindigkeiten und umfasst auch nicht-lineares Verhalten. Es wird gezeigt, dass für die Amplitude verschiedene Möglichkeiten bestehen, insbesondere das Unendlichwerden in einem endlichen Zeitabschnitt. Wellen höherer Ordnung werden kurz diskutiert.

     

Synthesis of thieno[2,3-c:5,4-c]dipyridine and the one electron transfer properties of its dimethyl diquaternary salt

Thieno[2,3-c:5,4-c]dipyridine is synthesised by reaction of 3,3′-thiobispyridine with sodium and liquid ammonia in dimethylformamide. It forms a diquaternary salt with excess methyl iodide. The salt is reversibly reduced to a stable blue-green radical cation in aqueous solution at a potential (E_σ) of -0.38V.     

Extended mode-hop-free tuning by use of a dual-cavity, pump-enhanced optical parametric oscillator

We report extended mode-hop-free tuning in a continuous-wave, pump-enhanced optical parametric oscillator (PE-OPO). We employ a dual-cavity configuration to allow independent control of the resonant pump and signal fields, and so we can suppress frequent mode hops in the signal as the pump is tuned in frequency. With the signal field clamped in frequency by an uncoated etalon, the idler field can be scanned smoothly through a range of 10.8 GHz. The PE-OPO outputs can also be tuned coarsely from 1.01 to 1.18 mum in the signal and from 2.71 to 3.26 mum and 4.07 to 5.26 mum in the idler. We find that increased idler absorption only slightly increases the oscillation threshold.     

Multiple-electron excitation in X-ray absorption: a simple generic model

The probability of multiple-electron excitation in X-ray absorption is calculated using a simple generic model. The model permits calculations to be made for all atoms with little input data or computing effort. The high-energy limit of this probability, which gives the usual EXAFS amplitude reduction factor, is calculated in the 'sudden approximation' using Slater orbitals. Good agreement with experiment is found. The energy dependence of this probability is also calculated using a simple model form of perturbing potential and found to agree well with experiment for rare gas atoms. The effect on the X-ray absorption coefficient of including multiple-electron excitations is also determined and is found to be small, again in agreement with observation.