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 31.7 million years; a ray of light travels approximately 0.3 µm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a virus.
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.
A femtosecond is one millionth of a nanosecond or 10 -15 of a second and is a measurement sometimes used in laser technology.
For comparison, a millisecond (ms or msec) is one thousandth of a second and is commonly used in measuring the time to read to or write from a hard disk or a CD-ROM player or to measure packet travel time on the Internet.
A microsecond (µs) is one millionth (10 -6 ) of a second.
A nanosecond (ns or nsec) is one billionth (10 -9 ) of a second and is a common measurement of read or write access time to random access memory ( RAM ).
A picosecond is one trillionth (10 -12 ) of a second, or one millionth of a microsecond.
An attosecond is one quintillionth (10 -18 ) of a second and is a term used in photon research.