A microsecond is a millionth (1*10^-6) of a second. It is often used for measuring things like atomic and chemical reactions, which occur in normally immeasurable amounts of time.
... covered by US patents 3,726,146 (1973) and 5,353,655 (1994) by L.A. Mishler and US patent 5,800,311 (1998) by P.S.Chuang.
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