Brillouin scattering has been measured with a high degree of sensitivity by a system built around a laser-diode-pumped microchip LiNdP(4)O(12) laser. An efficient self-mixing modulation effect that is due to the interference between a lasing field and a weak field fed back from an acousto-optic modulator by means of a phase-conjugate reflection was used. Laser-Doppler velocimetry that can discriminate the direction of motion has been demonstrated.

The origin of power-law distributions in self-organized criticality is investigated by treating the variation of the number of active sites in the system as a stochastic process. An avalanche is then regarded as a first-return random-walk process in a one-dimensional lattice. Power-law distributions of the lifetime and spatial size are found when the random walk is unbiased with equal probability to move in opposite directions. This shows that power-law distributions in selforganized criticality may be caused by the balance of competitive interactions. At the mean time, the mean spatial size for avalanches with the same lifetime is found to increase in a power law with the lifetime.

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One possible basis of a new definition of the kilogram is the Avogadro constant determined by measuring the lattice parameter and molar volume of a silicon single crystal. Data of molar volumes derived from different silicon crystals in the international framework differ significantly. It was suggested that the differences are produced by holes or voids in the crystal lattice exceeding today's experience in silicon perfection. To illuminate this problem, test crystals were grown in different ambient conditions in order to generate areas in the material with vacancies or light elements. Macroscopic defects were generated by hydrogen in the growth atmosphere and detected by preferential etching, laser scattering tomography and x-ray topography. Using the pressure-of-flotation method for the evaluation of density differences in silicon, relative loss in the macroscopic density of float-zone silicon up to 1 × 10 −7 was observed when the growth ambient contained 2% hydrogen. However, the reason for the reported molar volume differences of the order of 10 −6 is still not found and will be the subject of further investigations.(Some figures in this article are in colour only in the electronic version)