Cubic optical nonlinearity of free electrons in bulk gold

Abstract

A fast (Tau(response) <90 fs) free-electron spin-f lipping frequency-degenerate nonlinearity with a signif icant value of|chi((3))(xxyy)(omega,omega,omega,-omega)chi((3))(xxyy)(omega,omega,omega,-omega)|~10(-)(8)esu has been observed in bulk gold at 1260 nm by use of a new pump-probe polarization-sensitive technique.