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.[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 word femtosecond is formed by the SI prefix femto and the SI unit second. 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.

Shorter Times

Longer Times

See also


  1. "Femtosecond: Merriam Webster definition". Merriam Webster Online Dictionary.
  2. Compared with overview in: Fisher, Bruce; Harvey, Richard P.; Champe, Pamela C. (2007). Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series). Hagerstown, MD: Lippincott Williams & Wilkins. ISBN 0-7817-8215-5. Page 3
  3. NIST. "NIST Definitions of the SI units".
  4. "Femtosecond: use in molecular dynamics simulation". LAMMPS Molecular Simulator.
  5. 1 2 3 4 Andrew M. Weiner (2009). Ultrafast Optics. Wiley. ISBN 978-0-471-41539-8.
  6. Abbi, S. C. (2001). Nonlinear Optics and Laser Spectroscopy. United States of America: Alpha Science Int'l Ltd. p. 361. ISBN 8173193541.
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