This is the free portion of the full article. The full article is available to licensed users only.
How do I get access?

Femtosecond

A unit of time equa to 10−15 s (seconds), i.e., one billionth (U.S.) of one millionth of a second, which corresponds to a frequency of one petahertz (1 PHz), about the frequency of visible violet light with a wavelength of about 0.3