# atto- [A toh]

#### (Danish or Norwegian: eighteen; a decimal prefix used in the international metric system for measurements)

This prefix is used in the metric [decimal] system as quintillionth [U.S.] and trillionth part [U.K.], 10-18 [0.000 000 000 000 000 001]. The metric symbol for atto- is a.

attoampere (aA)
One-quintillionth (10-18) of an ampere.

The ampere, in practice often shortened to "amp", (symbol: A) is a unit of electric current, or amount of electric charge per second.

The ampere is an SI base unit, and is named after André-Marie Ampère (born, January 22, 1775 Poleymieux, Lyon, France and died June 10, 1836, in Marseille, France), one of the main discoverers of electromagnetism.

The farad is defined as the amount of capacitance for which a potential difference of one volt results in a static charge of one coulomb.

Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential.

A coulomb (symbol: C) is the SI unit of electric charge. It is named after Charles Augustin de Coulomb who was a French physicist.

attogram, ag
A unit of mass equal to 10-18 grams; symbol: ag.
attoscience
The study of the physical processes which occur in less than a fraction of a cycle of visible light, in times less than a quadrillionth of a second.
attosecond (as)
1. One attosecond (as) is equivalent to the time it takes for light to cross an atom.
2. One quintillionth of a second; one thousandth of a femtosecond.
3. There are 1,000,000,000,000,000,000 (translated as a million trillion) attoseconds in one second.
— Source for this atto (as) word: Chemistry and Molecular Biology Resources, UC Extension, Berkeley/San Francisco

In February, 2004, a team of physicists led by Dr. Ferenc Krausz (Austria) of Vienna University of Technology, announced that they had created pulses of ultraviolet laser light lasting just 250 attoseconds (250 times 10-18 seconds). Using these attosecond light pulses, they were able to observe electrons in neon atoms and distinguish between events just 100 attoseconds apart.

A statement of goals by Attoworld: "Our primary research goal is to develop tools and techniques enabling us to control the motion of electrons on atomic length and time scales and observe these motions in space and time with sub-atomic (picometre and attosecond) resolution."

—More atto information is available at Atto World.

### Watching electrons tunnel, German-Austrian-Dutch team observes electron tunnelling for the first time

It has been predicted that ionization of atoms in strong electromagnetic fields occurs via a quantum mechanical process: electrons ovrecome the attractive force of the atomic core by tunnelling through the potential wall.

Now for the first time (Nature, April 5, 2007) a German-Austrian-Dutch collaboration around professor Ferenc Krausz, Director at the max Planck Institute of Quantum Optics, has succeeded in capturing this process in real time.

Using ultrashort laser pulses the scientists were able to reveal distinct steps of ionization each lasting several hundred attoseconds.

The result represents a milestone in gaining deeper insight into electronic motion inside atoms and molecules, which is relevant to advancing many areas of science, technology, and medicine.

—Information from the "Joint Press Release of the
Max Planck Institute of Quantum Optics and the
Munich Centre for Advanced Photonics", April 5, 2007;
as seen in the Atto World web site.

attotesla (aT)
One-quintillionth (10-18) of a tesla or aT.

The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction) and defines the intensity (density) of a magnetic field.

The tesla is equal to one weber per square meter and was defined in 1960 in honor of the inventor, scientist, and electrical engineer Nikola Tesla.

In physics, the weber (symbol: Wb) is the SI unit of magnetic flux. It is named after the German physicist Wilhelm Eduard Weber (1804-1891) and was established by the IEC in 1930.

The IEC refers to the International Electrotechnical Commission which is a not-for-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic, and related technologies; collectively known as "electrotechnology".

attowatt (aW)
One-quintillionth [U.S.] and trillionth part [U.K.], of a watt, 10-18 [0.000 000 000 000 000 001], the approximate power scale at which operations of nanoelectromechanical systems is overwhelmed by thermal fluctuations.

Related "metric" families: yotta; zetta; exa; peta; tera; giga; mega; kilo; hecto; deka; deci; centi; milli; micro; nano; pico; femto; zepto; yocto.