femtosecond
A unit of time equal to 10⁻¹⁵ seconds. Used in physics, chemistry, and ultrafast optics.
Femtosecond lasers are used to observe ultrafast phenomena.
Chemical reactions can occur on a femtosecond timescale.
From the SI prefix フェムト (femto-, 10⁻¹⁵) and 秒 (second).