CO laser stabilization using the optogalvanic Lamb-dip

Frequency stabilization of the CO laser using a CO lamb-dip is achieved in the range from 5.0–6.3 m. The CO saturation signal is obtained from a low-pressure discharge in absorption and is detected using optogalvanic, detection. The frequency stability and reproducibility has been verified to be better than 100 kHz; this is an improvement of more than one order of magnitude compared with locking techniques using CO laser gain profiles.Alexander von Humboldt Awardee from National Bureau of Standards, Boulder, Colorado, USA     

Multiparticle excitations in142Nd

An (α, 2nγ) in-beam study of excited states in 142Nd revealed 27 new levels on top of the 6⁺ isomer. Nanosecond lifetimes were found for two levels. The measured excitation energies were compared with spherical shell-model predictions obtained from suitably truncated model spaces.     

Vibrational modes and infrared absorption of interstitial oxygen in silicon

A quasi-linear Si₂O molecule model (QLMM) is suggested from an analysis of the configuration and the interactions of an isolated oxygen atom with its neighbor silicon atoms. The vibrational modes are assigned and the infrared absorption spectra are calculated in detail with the model. The theoretical results are in reasonably good agreement with reported experimental values. This agreement shows that for the analysis of the vibrational modes of the interstitial oxygen atom in silicon crystals it is not necessary to consider the coupling of the molecule with the rest of the lattice. The interaction of the oxygen atom with its six second-nearest silicon atoms only causes the level separation of the ₂ mode and the formation of the fine structure.     

Toward molecular electronics

A polarized N-O bond behaves as an intramolecular p-n junction. Their rectifying properties have been found in 1,3-dimethylisoxasole, 1-phenylsydnone, and 1-(4-methylphenyl)sydnone molecules based on H¹-NMR data.     

High energy muon-nucleon inelastic scattering at lowq 2

The inelastic interactions of 150 GeV positive muons produced at Fermi Laboratory have been studied in nuclear emulsion. Secondary particles produced in these interactions have been identified, the energy spectra and angular distributions for pions and protons are given. The inclusive pionproduction reaction is studied and the relative shape ofp _t ² distribution is discussed. The average charged multiplicity relations are determined as a function of different parameters and are compared with the multiplicities produced in pure hadronic interactions. The integral cross sections have been measured and are compared with the first and second powers of 1/(1+q ²/m _p ² ) forσ _exp(q ²,v), the quantity commonly called the “virtualphoton-nucleon total cross section”. The values of the structure function νW ₂ are calculated for 0.02≤q ²≤0.5. The present data are compared with other muon data at the same energy.     

Analysis of the 3-dimensional electron distribution in silicon using directional Compton profile measurements

A method of reconstructing the electron momentum density (p), and its Fourier transform,B(t), from a series of directional Compton profiles is described. It is based on a double Fourier inversion technique and an expansion in lattice harmonic functions. The effect of random errors has been analysed, and the implications for the data collection discussed. We have used the reconstruction technique to obtain (p) andB(t) for silicon from six directional Compton profiles measured with 412 KeV gamma-radiation. The experimental result is in good agreement with earlier measurements and with available solid state theories. A recent Wannier function calculation for silicon using orthogonalised bond orbitals provides a useful tool for identifying the physical origins of the observed anisotropies. A comparison between the information presented in position and momentum space shows that the ease of interpretation depends upon the degree to which the various interactions give rise to localised features in each representation.     

The effect of laser illumination on the propagation of ultrasonic waves in single crystalline lithium niobate

By means of ultrasonic experiments we have observed in Fe-doped LiNbO₃-crystals elastic inhomogeneities and an ultrasonic absorption which stronglydecrease under laser illumination. The elastic inhomogeneities before illumination lead to a non-exponential decay of the ultrasonic echo pattern. The corresponding variations of the acoustic velocity and absorption across the sound beam have been displayed directly by an ultrasonic topography. — In contrast to the photorefractive behaviour of LiNbO₃ the elastic inhomogeneities and the ultrasonic absorption are not enhanced but disappear as soon as the illumination is switched on: Under illumination the echo pattern becomes well exponential as expected for an ideal crystal. The physical nature of the elastic inhomogeneities and the acoustic absorption inside the sample which can be bleached out by optical radiation is not yet well understood. But there is evidence that Fe⁺⁺-impurities play an important role.Dedicated to Professor Harry Thomas on the occasion of his 60th birthdaySupported by the Science Fund of the Chinese Academy of Sciences