The advent of the modelocked Ti:sapphire laser in the late 1980s was a major milestone in the generation of subpicosecond and femtosecond optical pulses and ultimately led to the all-solid-state ultrafast laser systems with which we are familiar today. As the laser systems evolved, becoming much more robust and user-friendly in the process, so too did the range of ultrafast applications. In research labs, femtosecond pulses now enable routine real-time monitoring of molecular chemistry processes, while on the factory floor they can deliver direct-write, precision materials processing.
Despite its tremendous properties as a gain medium however, the Ti:sapphire crystal does manifest thermally induced optical distortion when pumped. Although attention to system design can compensate for much of this lensing effect, one rather unusual route to its management at higher powers is cryogenic cooling of the Ti:sapphire crystal, resulting in an even more versatile ultrafast system (see cover and p. 65).
Besides their direct applications, femtosecond pulses can also be used to generate attosecond pulses (10-18 s.) in the extreme-UV. And while femtosecond pulses opened the door to directly probing molecular chemistry mechanisms, attosecond pulses similarly will “open a new window on atomic physics,” says contributing editor Jeff Hecht, by providing a means to examine electronic transitions in atoms (see p. 103).
“Materials processing” is an awkwardly broad term that actually groups countless laser applications, from welding sheet metal to precision machining, and from the newest technology to the not so new. While ultrafast materials processing is still relatively novel and particularly suited to situations in which excess heat is a problem (the speed of the pulse means it can do its processing job before producing residual heat), processing materials with excimers is well established. And low thermal damage to the surroundings is also one of its benefits-in this case because of the short (UV) wavelengths. From drilling nozzles to the micromachining of polymers and ceramics, the excimer laser offers a set of unique benefits in precision materials processing (see p. 69).