Interactions of laser light with solids. The term usually refers to the thermal effects of absorption of high-intensity laser beams. For nonthermal laser interactions with matter See Laser spectroscopy, Nonlinear optics
The high power densities attainable with lasers allow melting and even vaporization of any solid material that is sufficiently opaque at a given wavelength or photon energy. This has led to a number of applications involving cutting and drilling of ceramics and other brittle materials, even diamonds. Welding of components from the smallest wires to huge steel plates is done commercially with high-power lasers. Metal alloying in surface regions is also a domain of lasers.
Ion implantation has become a dominant method of introducing controlled quantities of impurities near the surface of silicon and other semiconductors. The implanted layers need a heat treatment to repair the displacement damage caused by bombardment with energetic ions and to move the implanted impurity ions into lattice locations where they replace host atoms and become electrically active. Laser heating is particularly suitable for annealing since only the implanted regions are heated.
Thin films of single-crystalline silicon over an insulating substrate are very attractive for high-speed integrated circuits. An important approach to the formation of such films is the controlled melting of thin polycrystalline layers deposited over fused silica substrates or over oxidized silicon wafers. Through a careful control of temperature gradients around the molten spot, by shaping the laser beam or patterning the film, single-crystalline regions can be obtained. The formation of silicon-on-insulator structures will lead in the future to three-dimensional circuits, with several levels of transistors on the same chip. See Laser