A
femtosecond is the
SI unit of time 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. 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.