Another important technique enabled by femtosecond laser pulses is welding of transparent materials, e.g. glass or polymers. The laser beam is focused at the interface between the two materials to be welded. Because of nonlinear absorption, only the region around the laser focus melts to create the weld. Even though a single laser pulse deposits minimal heat in the material, rapid, overlapping pulses can be used to produce precise thermal effects at the laser focus through heat accumulation. Precise control of the thermal effect can be achieved by varying the translation speed and pulse repetition rate.