Meteoritic dust from the atmospheric disintegration of a large meteoroid.

Much of the mass of most meteoroids entering the Earth's atmosphere is consumed in the process of ablation. Larger meteoroids (> 10 cm), which in some cases reach the ground as meteorites, typically have survival fractions near 1-25 per cent of their initial mass. The fate of the remaining ablated material is unclear, but theory suggests that much of it should recondense through coagulation as nanometre-sized particles. No direct measurements of such meteoric 'smoke' have hitherto been made. Here we report the disintegration of one of the largest meteoroids to have entered the Earth's atmosphere during the past decade, and show that the dominant contribution to the mass of the residual atmospheric aerosol was in the form of micrometre-sized particles. This result is contrary to the usual view that most of the material in large meteoroids is efficiently converted to particles of much smaller size through ablation. Assuming that our observations are of a typical event, we suggest that large meteoroids provide the dominant source of micrometre-sized meteoritic dust at the Earth's surface over long timescales.

Small-core single-mode microstructured polymer optical fiber with large external diameter.

A preform sleeving technique is demonstrated that allows the fabrication of single-mode polymer microstructured fiber with the smallest core and hole dimensions yet reported to our knowledge. For a fixed triangular hole pattern a range of fibers is produced by adjustment to the operating conditions of the draw tower. Numerical modeling is carried out for one of the fibers produced with a 570-microm external diameter, a core diameter of 2.23 microm, an average hole diameter of 0.53 microm, and an average hole spacing of 1.38 microm. This fiber was shown to be endlessly single mode.

Identifying hollow waveguide guidance in air-cored microstructured optical fibres.

An analysis of leaky modes in real microstructured optical fibres fabricated specifically for photonic band gap guidance in an air core has been used to identify alternative guiding mechanisms. The supported leaky modes exhibit properties closely matching a simple hollow waveguide, uninfluenced by the surrounding microstructure. The analysis gives a quantitative determination of the wavelength dependent loss of these modes and illustrates a mechanism not photonic band gap in origin by which colouration can be observed in such fibres. These findings are demonstrated experimentally.