surface interactions. They can yield valuable information complementary to that obtained by other means. The field is still in the beginning stage: the existing techniques need further development, and many other possible techniques are yet to be explored. The practical importance of this research area is evidenced by the recent entrance of many industrial and national laboratories into the field.

Lasers already play a significant role in the area of surface processing. Although most of the laser techniques are still in the developmental stage, a few have reached the production line. Laser annealing is probably the best-known process: the recrystallization of the surface after laser-induced melting can yield high-quality crystalline films. With a pulsed laser, it is even possible to obtain selectively a crystalline or amorphous film depending on the duration of the pulse. Laser heating of surfaces is also the basis of a number of other laser surface-processing techniques. These include laser-enhanced etching, laser-enhanced electroplating, and laser alloying. In the former two cases, a continuous-wave laser beam can enhance the processing speed by orders of magnitude. In the latter, pulsed laser alloying with extremely rapid quenching can yield alloy films obtainable by ordinary methods. In all these cases, laser heating has the advantage of being able to heat a local spatial region selectively to a very high temperature. The spatial resolution of such laser processing techniques would be limited only by the degree to which the laser can be focused. Aside from laser heating, laser-induced chemical reactions can also be used to modify surfaces. Photochemical surface etching or deposition is one example. Micron-size metal or nonmetal structure can be inscribed on a surface at high speed using such a process. Laser ablation can also be an effective method for surface processing. With ultraviolet lasers, the technique can carve extremely sharp surface patterns on polymers or biological materials. This is believed to be the result of laser-induced bond breaking rather than thermal evaporation.

All of these laser processing techniques hold considerable promise as practical tools for surface treatment. Many industrial labs have already invested heavily in the development of these techniques. One might think that the basic physics underlying these laser processes must be well understood. This is not true, however, and universities in collaboration with industrial laboratories can expect to make significant contributions.



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