Phase transformations of crystalline ${\text{Ge}}_2{\text{Sb}}_2{\text{Te}}_5$ films upon pulsed laser irradiation have been studied using in situ reflectivity measurements with temporal resolution. Two different configurations allowed point probing with nanosecond temporal resolution and imaging with subpicosecond temporal and micrometer spatial resolution. The role of the pulse duration and laser fluence on the dynamics of the phase change and the degree of amorphization is discussed. Several advantageous features of femtosecond compared to nanosecond laser-induced amorphization are identified. Moreover, a high-resolution study of the amorphization dynamics reveals the onset of amorphization at moderate fluences to occur within $\sim 100\text{ps}$ after arrival of the laser pulse. At high fluences, amorphization occurs after $\sim 430\text{ps}$ and the molten phase is characterized by an anomalously low reflectivity value, indicative of a state of extreme supercooling.

A new class of partially coherent light sources is introduced. At the source plane, they exhibit perfect coherence along any annulus that is concentric to the source center. Between two points at different distances from the center, coherence can be partial or even vanishing. Such sources can be synthesized by using a generalized form of van Cittert–Zernike theorem where axial sources are used. Beams radiated by this type of source are analyzed at the source plane and upon free propagation for some simple cases.

Time-resolved measurements of the spectral dielectric function reveal new information about ultrafast phase transitions induced by femtosecond laser pulses in Sb-rich amorphous GeSb films. The excitation generates a nonthermal phase within 200 fs. The dielectric function of this phase differs from that of the crystalline phase, contrary to previous suggestions of a disorder-to-order transition. The observed dielectric function is close to that of the liquid phase, indicating an ultrafast transition from the amorphous phase to a different disordered state.

8 pages, 6 figures, 1 table.-- PACS: 78.66.Jg; 78.66.Nk; 78.20.Ci; 68.55.Ln; 07.60.Fs; 81.05.Ys; 68.55.JkSpectroscopic ellipsometry together with an effective medium model is used to determine simultaneously the effective refractive index, thickness, and metal volume fraction of thin nanocomposite films. The films are formed by Bi nanocrystals embedded in amorphous matrices, either semiconducting (Ge) or dielectric (Al2O3). For the Bi:Ge films (metal in an absorbing host), the values obtained for both the real and imaginary parts of the refractive index vary continuously from that of Ge to that of Bi. The metal contents determined from the ellipsometry analysis are in excellent agreement with those obtained from direct measurements of the composition. For the Bi:Al2O3 films (metal in a nonabsorbing host), the extinction coefficient (k) exhibits a maximum around 360 nm which is related to the metal plasmon resonance frequency of Bi nanocrystals. The metal content determined from the ellipsometry analysis in this case is underestimated, probably due to interaction of the Bi crystals with the Al2O3 host.This work has been partially supported by CICYT\ud (Spain) under TIC96-0467 project. The authors are grateful\ud to the GPS (Université de Paris VI et VII, France) for provision\ud and assistance of Rutherford backscattering facilities.\ud One of the authors (J.M.B.) greatly acknowledges a FPI\ud grant from the Spanish Ministry of Education and Culture.Peer reviewe

This paper presents a comprehensive review of the state-of-the-art developments in health monitoring of marine structures. Monitoring the health of marine structures plays a key role in reducing the risk of structural failure. The authors establish the different sensors with their theoretical foundations and applications in order to determine the optimal position of the sensors on board. Once the data were collected, it was necessary to use for subsequent treatment; thus, the authors identified the different methodologies related to the treatment of data collected by the sensors. The authors provide a historical review of the location of different sensors depending on the type of ship and offshore platform. Finally, this review paper states the conclusions and future trends of this technology.