New wave of laser welding using USLP

New wave of laser welding using USLP is presented in comparison with keyhole laser welding using CW lasers. The author has been involved in the research work on laser-matter interaction in laser welding process and applied to in-process monitoring since 1965. It is shown that the welding performance of the keyhole welding is limited by humping, plasma shielding, collapse of keyhole, thermal deformation due to shrinkage stress and so on. Recently the author has developed a novel fusion welding process of transparent material using ultrashort laser pulse (USLP) where the laser energy is absorbed by nonlinear process. In USLP welding, the laser energy is deposited into plasma produced inside bulk material to produce embedded molten pool, in contrast to the case of the conventional keyhole welding where molten pool contains free surface. New wave of laser welding brought by USLP is introduced by showing that USLP can remove the limitations and/or problems such as maximum welding speed, minimum weldable thickness, plasma shielding and shrinkage thermal stress, which limit the performances of the conventional keyhole welding. The USLP welding of glass/glass and Si/glass are demonstrated to show how the problems encountered in the keyhole welding are overcome.