## Friday, 11 March 2016

### ONE FEMTOSECOND = ONE QUADRILLIONTH OF A SECOND

FEMTOSECOND (WIKI)

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 31.71 million years; a ray of light travels approximately 0.3 µm (micrometers) in 1 femtosecond, a distance comparable to the diameter of a virus.
The word femtosecond is formed by the SI prefix femto and the SI unit second. Its symbol is fs.
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.
• 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.
• 1.3 fs – cycle time for 390 nanometer light, at the transition between violet visible light and ultraviolet
• 2.57 fs – cycle time for 770 nanometer light, at the transition between red visible light and near-infrared
• 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
• 300 fs – the duration of a vibration of the atoms in an iodine molecule