In surgery, the system that uses a femtosecond flash of light: A femtolaser has been used to sever the axons that control muscles in nematode worms resulting in the immediate loss of the ability to wiggle backward; although they regenerated about half their axons, and some worms regained full movement within 24 hours.

"Femto<" is a combining form used in naming units of measurement to indicate one-thousand-million-millionth (10^-15) of the laser unit.

A "laser" is a device that transfers light of various frequencies into an extremely intense, small, and nearly nondivergent beam of monochromatic radiation in the visible or invisible spectrum, with all the waves in phase; capable of mobilizing immense heat and power when focused at close range, lasers act on tissues by photocoagulation and photodisruption and are used in surgery, in diagnosis, and in physiological studies.