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We investigated the laser-energy-density dependence of absorption changes and paramagnetic centers induced by a cw Ar(+)laser operating at 5.1 eV, in both unloaded and H(2)-loaded singlemode Ge-doped optical fibers. The induced absorption is measured in the blue and near ultraviolet spectral range by using the 3.1 eV photoluminescence, ascribed to Ge lone pair center (GLPC), as an in situ probe source. We find that the Ge(1) center (GeO-(4) ) is induced upon UV exposure by electron trapping on GeO(4) precursors, where the free electrons are most likely produced by ionization of GLPC. Ge(1) is responsible of optical transmission loss of the fiber in the investigated range. Hydrogen loading strongly influences the generation efficiency of the several observed paramagnetic defects, leading in particular to passivation of radiation-induced Ge(2) centers.

We report experimental results on the temperature and Ge-content dependencies of the decay times of the 3.1 eV emission of twofold-coordinated germaniums, excited at 3.51 eV, in both virgin and H2-loaded germanosilicate optical fibers. For T<110 K, the lifetimes are temperature invariant in the two kinds of fibers; at higher temperatures, they are progressively shortened in the H2-loaded fibers whereas they remain unaltered in the virgin fibers. On increasing the Ge content in the fiber core the lifetime decreases in the whole temperature range. We also found a direct correlation in H2-loaded samples between the dependencies on temperature of the emission lifetime and the diffusion lengths of H2 molecules in silica glass determined from earlier work. These experimental features are explained by assuming an elastic-collisional deactivation mechanism due to interaction with diffusing H2 molecules, described in terms of an Arrhenius law with activation energy approximately 64 meV that operates in competition with the normal radiative process.

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Since the discovery of the first planet outside the solar system in 1995, the detection of exoplanets has been an attractive and engaging scientific field. This article intends to present briefly the radial velocity method for detecting the presence of an unseen planet orbiting a star. Based on an experimental setup, the presentation resorts to the analogy between sound waves and light waves. In particular, they can undergo the Doppler effect from which the radial velocity can be determined. Because the Doppler effect is easier to observe for sound waves than for light waves, a Bluetooth speaker simulates a star. It rotates in a horizontal circle with a constant angular speed, while emitting at two user-selected frequencies, simulating two spectral lines of a star. From the analysis of spectrograms, the radial velocities are deduced. Very good agreement is found between the experiment and theory.