Spallation caused by shock waves in optical components such as those used in the Laser MegaJoule facility during laser operation leads to material fracture during a Laser-Induced damage event. One solution may be to use a viscoelastic thin film on these components to mitigate spallation, but it must have excellent optical, mechanical, and resistance to laser damage properties. Among the viscoelastic materials investigated were Nafion and polydimethylsiloxane-based Ormosil. These materials, as thin films deposited on a fused silica substrate, were studied under nanosecond pulsed lasers at 1064 and 532 nm with different diagnostics in situ and post-mortem. In particular, the effect of the films on spallation was studied using the laser shock technique. Preliminary results showed that these thin films have interesting properties that could help to reduce mechanical damage to optical components.
we present a numerical and experimental study on the characterization of the temporal ablation pressure due to a laser with and without a confinement layer on aluminum target. Based on velocimetry measurements, we have built a large experimental data of laser configurations varying the pulse duration, the energy and the wavelength. Then we are able to reproduce the results with a single numerical model using the lagrangian 1D ESTHER hydrocode in both regimes. Finally we use the code to propose analytical laws for temporal ablation pressure in a large interaction domain for aluminum targets.
Spallation effects caused by shock waves in optical components such as those used in the Laser MegaJoule facility during laser operation can lead to material fracture. One solution could be to use a viscoelastic thin film on these fused silica components to reduce the reflection of shock waves from the rear surface, but it must have excellent optical, mechanical, and power-handling properties. Among the viscoelastic materials investigated were Nafion and polydimethylsiloxane-based ormosil, with ormosil synthesized using a sol-gel process. The materials were characterized optically and especially tested for acoustic attenuation. These materials, as thin films deposited on a fused silica substrate, were studied under shock wave propagation using the laser shock technique. Preliminary results showed that these thin films have interesting properties that could help reduce mechanical damage to optical components.
Structured Light Systems (SLS) give access, without contact, to a rich measurement of a cloud of points belonging to a same object surface. SLS received much interest in the past years and became a standard technique. The aim of this talk is to present the design of such a means, working in the visible spectrum, dedicated to shock physics (implying velocities up to several km/s) and to provide an example of measurements with a 3D reconstruction. A dedicated development is necessary (laser lighting, speckle smoothing, ambient light canceling, depth of field improvement), since commonly developed SLS don’t suit this field of study, mainly for three reasons: phenomena of interest (usually lasting a few microseconds) require extremely short exposure durations (few nanoseconds to few hundreds of picoseconds); the field of view ranges from millimeter for samples shocked by high power lasers to decimeter for high-explosive setups ; and finally, experimentations have single-shot acquisitions. The main domains of study are fragmentations, surface deformations and associated damages, like micro-spalling or ejected particle clouds.
In order to control laser-induced shock processes, two main points of interest must be fully understood: the laser–matter interaction generating a pressure loading from a given laser intensity profile and the propagation of induced shock waves within the target. This work aims to build a predictive model for laser shock-wave experiments with two grades of aluminum at low to middle intensities (50 to 500 GW/cm2) using the hydrodynamic Esther code. This one-dimensional Lagrangian code manages both laser–matter interaction and shocks propagation. The numerical results are compared to recent experiments conducted on the transportable laser shocks generator facility. The results of this work motivate a discussion on the shock behavior dependence to elastoplasticity and fracturation models. Numerical results of the rear surface velocity show a good agreement with the experimental results, and it appears that the response of the material to the propagating shock is well predicted. The Esther code associated to this developed model can therefore be considered as a reliable predictive code for laser ablation and shock-wave experiments with pure aluminum and 6061 aluminum in the mentioned range of parameters. The pressure–intensity relationship generated by the Esther code is compared to previously established relationships.
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