Short and intense Iaser pulse can process the surface and the inside oftransparent materials by focusing the pulse at desired position. Processing ofsuch a transparent material is considered to be app]icable to a lot of practica] applications.Details of such process are, however, still unclear and are subjects of fhrther investigations. Here we report on dynamical observation about interaction of fundarnental radiation (1064nm) of the Q-switched Nd:YAG laser to the surface of PMMA obseryed by an imaging system with nanosecond time resolution, The system uses fundamental radiation ofa Q-switched Nd:YAG laser as a processing laser and second harrnonic radiation (532nm) of another Nd:YAG laser as illuminating light.We observed stress wayes which propagate into the material and into the atmosphere by shadowgraph, schlieren and photoelastic method.We distinguished three different types of waves propagating into the bulk samples.The contrast of photoelastic images depends on raser pulse energy, Based on this result, we try to examine the effects of incidence angle of the laser to coupling between ]aser radiations and the material and found that magnitude ofstress wave correlates with laser fluence.
We report on dynamical observation about interaction of the fundamental radiation from a Q-switched Nd:YAG laser to the surface of PMMA observed by an imaging system with nanosecond time resolution, with special emphasis on stress waves inside the sample. We observed stress wave which propagated into the material and a pressure wave propagated into the atmosphere by shadowgraph and photoelastic methods. In the shadowgraph images, a shadow corresponded to the longitudinal elastic wave was clearly observed in the bulk. In photoelasticity images, another contrast which should correspond to the transverse wave was also observed. The contrast ofthe photoelasticity images depended on laser pulse energy. The contrast and thus the amount of absorbed energy were affected by the surface roughness: roughness greater than 1 micrometer caused complete absorption of laser energy at the surface. Based on this result, we try to examine the effects of incidence angle of the laser to coupling between laser radiations and the material.
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