Attosecond

An attosecond is 1×10⁻¹⁸ of a second (one quintillionth of a second). For context, an attosecond is to a second what a second is to about 31.71 billion years.

The word "attosecond" is formed by the prefix atto and the unit second. Atto- was made from the Danish word for eighteen (atten). Its symbol is as.

An attosecond is equal to 1000 zeptoseconds, or  ¹⁄₁₀₀₀ of a femtosecond. Because the next higher SI unit for time is the femtosecond (10⁻¹⁵ seconds), durations of 10⁻¹⁷ s and 10⁻¹⁶ s will typically be expressed as tens or hundreds of attoseconds:

Times which can be expressed in attoseconds: