A femtosecond is a unit of time in the
International System of Units (SI) equal to 10−15 or 1⁄1 000 000 000 000 000 of a
second; that is, one quadrillionth, or one millionth of one billionth, of a second.[1] For context, a femtosecond is to a second as a second is to about 31.71 million years; a ray of light travels approximately 0.3
μm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a
virus.[2] The first to make femtosecond measurements was the Egyptian Nobel Laureate Ahmed Zewail, for which he was awarded the Nobel Prize in Chemistry in 1999. Professor Zewail used lasers to measure the movement of particles at the femtosecond scale, thereby allowing chemical reactions to be observed for the first time.
The word femtosecond is formed by the
SI prefixfemto and the
SI unitsecond. Its symbol is fs.[3]
A femtosecond is equal to 1000
attoseconds, or 1/1000
picosecond. Because the next higher SI unit is 1000 times larger, times of 10−14 and 10−13 seconds are typically expressed as tens or hundreds of femtoseconds.
The
periods of the waves of visible
light have a duration of about 2 femtoseconds. The precise duration depends on the energy of the
photons, which determines their color. (See
wave–particle duality.) This time can be calculated by dividing the
wavelength of the light by the
speed of light (approximately 3×108 m/s) to determine the time required for light to travel that distance.[5]