Spall at ultra high strain rate (107 s−1) was investigated using short pulsed laser-induced shock waves in copper and aluminum foils. The intensities of the 3.9-ns Nd:Glass laser were in the range of 1010–1012 W/cm2, and the foil thickness was in the 100–600 μm range. The laser-generated shock wave pressure was in the range of a few hundred kilobars (kb). The shock wave traversed the foils in a few tens of nanoseconds. The controlled stepwise increase in laser energies allowed the stages of damage evolution from incipient to complete perforation of the target foils to be found. The energy threshold for spall and the spall width at that energy was measured as a function of the foil thickness for both materials. At threshold energy conditions, spall width of 25–65 μm for Al and 15–45 μm for Cu were obtained for foil thicknesses of 100–600 μm. Computer simulations of the laser-induced spall were performed, including the laser absorption, shock wave travel through the foil, and the spall phenomena. The simulations were based on the one-dimensional medusa code, which was expanded to include the spall phenomena, using simple spall criteria. An estimate of the strain rate was derived from the simulations and it was shown that the strain rates in the present experiments are about an order of magnitude larger than those obtained in spall experiments using other methods. The experimental results of energy threshold for spall and spall width at this energy were compared with the numerical simulations. The experimental results are in good agreement with the simulation results, indicating that spall strength for both materials, Al and Cu, are in the −50 to −60 kb regime.

An organically doped sol−gel optical fiber pH sensor based on silica-entrapped α-naphtholphthalein, is described. The absorption-based device, pumped with a red He−Ne laser, exhibits a dynamic range of 100% change between pH 4 and 11. The design and setup are simple and low cost, and the recladded optical fiber probe is easily replaceable.

Facile replication of microoptical elements and arrays was performed in sol-gel matrixes prepared by the fast sol-gel method. These sol-gel resins, made from mixtures of alkylalkoxysilane monomers, undergo hydrolysis and polymerization within 10-20 min and curing within a few days. Single-step reproducible fabrication of large crack-free elements of 1 cm thickness and up to 10 cm in diameter was demonstrated. High accuracy of replication was facilitated by maintaining a very small shrinkage of only a few percent during the curing stage. This was attained by removing most of the volatile products from the sol, without gelling, prior to casting it onto the template. Accurate replication depends on adequate control of two key parameters: the replica-template adhesion-separation timing, by manipulating the template surface via oxidative etching, and the drying-cross-linking relative pace, by accurately tailoring the silanes mixture, the water-to-silane ratio, and their hydrolysis and polymerization.

Experimental confirmation is provided for a brittle-to-ductile transition of the spall failure mode in a 6061-T6 aluminum alloy, at a strain rate of 107 s−1 , caused by laser-induced shock waves. This result is consistent with the prediction of a theory that has been put forward recently by Grady. The experimental approach that was used allowed determination of the maximum elongation associated with the spall failure in the alloy and pure aluminum.

A new experimental method was developed in order to estimate the decay of the laser-generated shock waves and the dynamic spall pressure. Experiments were performed on aluminum, copper, and unidirectional carbon fiber epoxy composites with impact strain rates of the order of 107 s−1. The following values for dynamic spall pressure and pressure gradient were obtained (to an accuracy of a factor of two): aluminum [25 kb (kb=kilobars), 60 kb/mm]; copper (20 kb, 180 kb/mm); carbon fiber epoxy composite (0.3 kb, 15 kb/mm) perpendicular to the fiber direction; and (7 kb, 100 kb/mm) when the impact is parallel to the fiber direction.