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Expimental setup showing focusing shock-wave generation and imaging. A mJ laser "shock"pulse was directed onto an axicon conical prism and focused by a lens to form a ring pattern at the sample layer. The laser induced shock wave, generated directly in the sample layer, propagates laterally within the layer. The shock evolution is evaluated either from CCD or streak camera images. After each image is recorded, the target is shifted to a new position with a fresh area in the beam paths since each irradiated and shocked sample region is permanently damaged.
Laser induced Shock Waves
The use of pulsed lasers to excite shock waves has considerably widened the possibilities for study of shock propagation and the dynamic properties of materials under shock loading. In almost all laser shock research conducted to date, an intense light pulse irradiates a thin layer of material (such as aluminum) which, through ablation or chemical decomposition, acts as a shock transducer and launches a shock pulse into an underlying material layer or substrate that includes the sample of interest. The shocked sample is typically probed optically from the opposite side through interferometric and/or spectroscopic measurements. However, the different sample regions at which the shock wave arrives at different times are not resolved spatially in the measurement. Spatially distinct probing regions will enable shock imaging as well as wide-ranging spectroscopic measurements spanning many spectral regions.
One of our recent experiments demonstrate laser-induced 2D focusing shock waves and direct, real-time visualization of shock-wave generation, in-plane propagation and focusing, and induced material responses. Following pulsed laser excitation of a thin sample, the shock wave propagates laterally in the plane of the sample rather than through the sample plane as in the front-back approach described above. In the present case, the optical excitation or laser ‘‘shock’’ pulse is focused to a circular ring pattern at the sample, launching a shock wave that propagates and focuses inward toward the center, see the drawings below.