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| A '''femtosecond''' is the [[SI unit]] of time equal to 10<sup>−15</sup> of a second. That is one quadrillionth, or one millionth of one billionth, of a [[second]].<ref name=Webster>{{cite web |title = [[Merriam Webster]] Online Dictionary |url = http://www.merriam-webster.com/dictionary/femtosecond |title = Femtosecond: Merriam Webster definition }}</ref> 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 [[Micrometer|µm (micrometers)]] in 1 femtosecond, a distance comparable to the diameter of a [[virus]].<ref name=Microbiology3>Compared with overview in: {{cite book |author=Fisher, Bruce; Harvey, Richard P.; Champe, Pamela C. |title=Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series) |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year= 2007|pages= |isbn=0-7817-8215-5 |oclc= |doi=}} Page 3</ref>
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| The word '''femtosecond''' is formed by the [[SI prefix]] ''femto'' and the [[SI unit]] ''second''. Its symbol is '''fs'''.<ref name="NIST">{{cite web |title = NIST Definitions of the SI units |url = http://physics.nist.gov/cuu/Units/prefixes.html |author = [[NIST]] }}</ref>
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| A femtosecond is equal to 1000 [[attosecond]]s, or 1/1000 [[picosecond]]. Because the next higher SI unit is 1000 times larger, times of 10<sup>−14</sup> and 10<sup>−13</sup> seconds are typically expressed as tens or hundreds of femtoseconds.
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| [[Attosecond|Shorter Times]]
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| * Typical time steps for [[molecular dynamics]] simulations are on the order of 1 fs.<ref name=LAMMPS>{{cite web |title = [[LAMMPS]] Molecular Simulator |url = http://lammps.sandia.gov/doc/run_style.html |title = Femtosecond: use in molecular dynamics simulation }}</ref>
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| * The waves of visible [[light]] oscillate with a [[period (physics)|period]] (reciprocal [[frequency]]) of about 2 femtoseconds <math>{\lambda\over{c}} = {(600\times10^{-9})\over{(3\times10^8)}} = 2.0\times10^{-15}</math>. The precise period depends on the energy of the [[photon]]s, 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 10<sup>8</sup> m/s) to determine the time required for light to travel that distance.<ref name=Weiner>{{cite book |title = Ultrafast Optics |author = Andrew M. Weiner |url = http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471415391.html |isbn = 978-0-471-41539-8 |year = 2009 |publisher = Wiley }}</ref>
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| ** 1.3 fs – cycle time for 390 [[nanometer]] light, at the transition between violet visible light and [[ultraviolet]]<ref name=Weiner/>
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| ** 2.57 fs – cycle time for 770 nanometer light, at the transition between red visible light and near-[[infrared]]<ref name=Weiner/>
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| * 200 fs – the swiftest [[chemical reaction]]s, such as the reaction of pigments in an [[Human eye|eye]] to light<ref name=Weiner/>
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| * 300 fs – the duration of a vibration of the atoms in an [[iodine]] molecule<ref>{{cite book |last = Abbi |first = S. C. |title = Nonlinear Optics and Laser Spectroscopy |url = http://books.google.com/books?id=bnuGcAZR14IC&pg=PA361 |year = 2001 |publisher = Alpha Science Int'l Ltd |location = United States of America |isbn = 8173193541 |page = 361 }}</ref>
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| [[Picosecond|Longer Times]]
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| == See also ==
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| * [[Femtochemistry]]
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| * [[Femtosecond pulse shaping]]
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| * [[SI unit]]
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| * [[Second]]
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| * [[Microsecond]]
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| * [[Millisecond]]
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| * [[Nanosecond]]
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| * [[Picosecond]]
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| * [[Orders of magnitude (time)]]
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| == References ==
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| {{reflist}}
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| {{Orders of magnitude seconds}}
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| {{DEFAULTSORT:1 E-15 S}}
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| [[Category:Orders of magnitude (time)]]
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| [[de:Sekunde#Abgeleitete Maßeinheiten]]
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| [[fr:1 E-15 s]]
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