Femtosecond

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

• Typical time steps for molecular dynamics simulations are on the order of 1 fs.^[4]
• The waves of visible light oscillate with a period (reciprocal frequency) of about 2 femtoseconds ${\lambda\over{c}} = {600 \times 10^{-9}~{\rm m} \over 3 \times 10^8~{\rm m}~{\rm s}^{-1}} = 2.0 \times 10^{-15}~{\rm s}$. The precise period 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 x 10⁸ m/s) to determine the time required for light to travel that distance.^[5]
  • 1.3 fs – cycle time for 390 nanometer light, at the transition between violet visible light and ultraviolet^[5]
  • 2.57 fs – cycle time for 770 nanometer light, at the transition between red visible light and near-infrared^[5]
• 15 fs – the swiftest chemical reaction, such as the absorption of a light photon in the Photosynthetic antenna molecule
• 200 fs – the average chemical reaction, such as the reaction of pigments in an eye to light^[5]
• 300 fs – the duration of a vibration of the atoms in an iodine molecule^[6]

Longer Times

See also

• Femtochemistry
• Femtosecond pulse shaping
• Ultrafast laser spectroscopy
• SI unit
• Second
• Microsecond
• Millisecond
• Nanosecond
• Picosecond
• Orders of magnitude (time)

References

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. 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.