A REVIEW OF ULTRASHORT PULSED-LASER ABLATION OF MATERIALS

The use of ultrashort pulsed lasers in materials processing is an emer ging technology. These lasers have the capability to ablate materials precisely with little or no collateral damage, even with materials tha t are impervious to laser energy from conventional pulsed lasers. The extreme intensities and short timescale at which ultrashort pulsed las ers operate differentiate them from other lasers. The means of ultrash ort pulsed laser generation is discussed; included are a survey of pul se compressor techniques with solid state lasers and a brief discussio n of excimer-dye lasers. This is followed by a discussion of specific examples of ultrashort pulsed machining of specific materials, along w ith mechanistic details. Optical breakdown mechanisms, including elect ron avalanche ionization and multiphoton absorption are discussed. It is shown that as pulse width increases and intensity decreases, laser damage becomes a stochastic process in which the ultrashort pulsed, hi gh intensity light causes optical breakdown over a very narrow range. This, along with the lack of significant thermal conduction, greatly i mproves the precision of ultrashort pulsed lasers in micromachining ap plications. (C) 1998 Laser Institute of America. [S1042-346X(98)00401- X].