Quantum and Thermal Interaction between Substances and Combined Laser Beams with Different Wavelength

点击翻译按钮获取中文摘要

The outline of results obtained in the research period from 1998 to 2001are summarized below.1) Effect of wavelength of laser on ablation processing characteristicsAblation hole drilling pheaoniena were materials. Laser wavelength used were the second high harmonic (λ=532 nm), third high harmonic (λ=355 nm) and fourth high harmonic (λ=266 nm) of Q-switched YAG laser. In the hole drilling of acrylic plate by the second and third high hamonics, there appeared heat affected zone around the hole in spite of nono-secorid pulse and cracking was generated after multiple laser irradiation. However, by the fourth high harmonics, the heat affected zone was hardly seen and the process became the quantum mode. Also, light emission behavior from plasma was studied and it was revealed that the interaction between incident beam and plasma gave significant effect of ablation process.2) Effect of combined laser beams with different wavelength on melting characteristics of various metalsThe combined las … More er beams with different wavelength, i.e., basic wavelength of YAG laser (l=1064 nm) and second high harmonics (SHG) of Q-switched YAG laser (l=532 nm) was irradiated on the various metals. It was revealed that the high reflective metals such as pure copper and aluminum could not melt by basic wave of YAG laser with peak power of 5 kW. However, the addition of small power SHG YAG laser (40 W) enhanced the melting efficiency greatly up to 130 percent. The similar effect was confirmed in other metals. In the lap welding of very thin sheet less than 0.1 mm in thickness, the basic wavelength YAG laser can not weld, but it was successfully welded when the combined laser beams were used.3) Direct observation of keyhole dynamics in laser weldingKeyhole behaviors in CW and pulsed laser welding were observed by X-ray transmission imaging system with high temporal resolution. In CW laser welding, the keyhole fluctuated quickly and this instability caused the porosity formation. While, in pulsed laser spot welding, a keyhole was quickly collapsed and metal vapor as well as shielding gas were confined in the keyhole when laser power was quickly terminated which led the formation of large porosity. The most effective way to suppress the porosity formation was the use of controlled pulse wave. Less