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The Optical Kerr Effect In Small Metal Particles And Metal-Doped Glasses : The Case Of Gold

Metal-doped glasses, composed of very small metallic particles embedded in a glass are known to be very efficient, fast-responding media for optical Kerr effects as phase conjugation in the degenerate - four - wave - mixing configuration. The origin of the high non-linearity of these media lies in the intrinsic electronic nonlinearity of metallic spheres which is greatly amplified by the existence of the surface plasma resonance. Such a resonance effect in the nonlinear optical properties is well understood from a general calculation of the response of a metal-doped glass to an electromagnetic radiation. We perform both theoretical and experimental studies of optical phase conjugation in the case of gold-doped glasses. Various origins of the nonlinearity of a gold sphere are analysed : conduction electron intraband contribution, saturation of direct interband transitions and change in dielectric constant due to hot photoexcited electrons. The last two are shown to be the most important contributions. Experimental studies of the dependence of the conjugate signal with the size of the spheres, and with the wave polarization of the beams confirm these conclusions. Saturation effects for absorption and phase conjugation are also fully understood.