femtosecond

{{Short description|One quadrillionth of a second}}

{{Infobox unit

| name = femtosecond

| image =

| caption =

| symbol = fs

| standard = SI

| quantity = time

| units1 = SI units

| inunits1 = {{val|e=-15|ul=s}}

}}

A femtosecond is a unit of time in the International System of Units (SI) equal to 10{{sup|−15}} or {{frac|1|1 000 000 000 000 000}} of a second; that is, one quadrillionth, or one millionth of one billionth, of a second.{{cite web |publisher= Merriam Webster Online Dictionary |url = http://www.merriam-webster.com/dictionary/femtosecond |title = Femtosecond: Merriam Webster definition }}

A femtosecond is to a second, as a second is to approximately 31.69 million years.

For context, a ray of light travels approximately 0.3 μm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a virus.Compared with overview in: {{cite book |author1=Fisher, Bruce |author2=Harvey, Richard P. |author3=Champe, Pamela C. |title=Lippincott's Illustrated Reviews: Microbiology (Lippincott's Illustrated Reviews Series) |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year= 2007|isbn=978-0-7817-8215-9 |page= 3}} The first to make femtosecond measurements was the Egyptian Nobel Laureate Ahmed Zewail, for which he was awarded the Nobel Prize in Chemistry in 1999. Professor Zewail used lasers to measure the movement of particles at the femtosecond scale, thereby allowing chemical reactions to be observed for the first time.

The word femtosecond is formed by the SI prefix femto and the SI unit second. Its symbol is fs.{{cite web |title = NIST Definitions of the SI units |url = http://physics.nist.gov/cuu/Units/prefixes.html |author = NIST |author-link = NIST }}

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.

• Typical time steps for molecular dynamics simulations are on the order of 1 fs.{{cite web |publisher = LAMMPS Molecular Simulator |url = http://lammps.sandia.gov/doc/run_style.html |title = Femtosecond: use in molecular dynamics simulation }}
• The periods of the waves of visible light have a duration of about 2 femtoseconds. $\{\backslash lambda\backslash over\{c\}\}\; =\; \{600\; \backslash times\; 10^\{-9\}~\{\backslash rm\; m\}\; \backslash over\; 3\; \backslash times\; 10^8~\{\backslash rm\; m\}~\{\backslash rm\; s\}^\{-1\}\}\; =\; 2.0\; \backslash times\; 10^\{-15\}~\{\backslash rm\; s\}$ The precise duration 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 3×10⁸ m/s) to determine the time required for light to travel that distance.{{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 }}

class="wikitable" style="float:center; width:400px; margin:1em 0 1em 1em; clear:right;" |+ The colors of the visible light spectrum{{cite book|title=Fundamentals of Atmospheric Radiation: An Introduction with 400 Problems|author=Craig F. Bohren|publisher=Wiley-VCH|year=2006|isbn=978-3-527-40503-9|url=https://books.google.com/books?id=VN2RC-xcKioC|page=214|bibcode=2006fari.book.....B}}
style="text-align: left" colspan="2"|Color !abbr="wavelength"|Wavelength interval !abbr="frequency"|Cycle time interval
style="background:#f00;"| !style="text-align: left"|Red | ~ 700–635 nm | ~ 2.3–2.1 fs
style="background:#ff8000"| !style="text-align: left"|Orange | ~ 635–590 nm | ~ 2.1-2.0 fs
style="background:#ff0"| !style="text-align: left"|Yellow | ~ 590–560 nm | ~ 2.0–1.9 fs
style="background:#0f0"| !style="text-align: left"|Green | ~ 560–520 nm | ~ 1.9–1.7 fs
style="background:#0ff"| !style="text-align: left"|Cyan | ~ 520–490 nm | ~ 1.7–1.6 fs
style="background:#00f"| !style="text-align: left"|Blue | ~ 490–450 nm | ~ 1.6–1.5 fs
style="background:#8000ff" | !style="text-align: left"|Violet | ~ 450–400 nm | ~ 1.5–1.3 fs