Optical Limitation induced by Gold Clusters. 1. Size Effect

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Optical Limitation induced by Gold Clusters. 1. Size Effect
Lionel Francüois, Mehran Mostafavi,* and Jacqueline Belloni
Laboratoire de Chimie Physique, UMR 8610 CNRS, UniVersite´ Paris-Sud, 91405 Orsay, Cedex, France
Jean-Francüois Delouis and Jacques Delaire
( C) F; x5 o, X4 E, u' dLaboratoire de Photophysique et Photochimie Supramole´culaires et Macromole´culaires, UMR 8531,
2 Q+ j" p+ B2 ]! n4 Y2 AEcole Normale Supe´rieure de Cachan, 94235 Cachan Cedex, France
Patrick Feneyrou
& v) _7 l- `( `; e/ z, \2 ?1 [Laboratoire Central de Recherches, Thomson-CSF, Domaine de CorbeVille, 91404 Orsay Cedex, France
7 }, N/ ~- E8 j8 I  ^ReceiVed: December 20, 1999; In Final Form: March 8, 2000
) K6 x  t0 w: _1 L: \) hThe nonlinear optical response of gold particles (with 2.5, 9, or 15 nm radius) prepared by ç-radiolysis in
/ e6 Z8 n3 _  K- u5 Awater solution and stabilized by poly(vinyl alcohol) is size-dependent. The 2.5 nm clusters do not limit light
transmission even at very high fluence of nanosecond laser pulses, while the larger clusters strongly limit the
laser beam transmission at 530 nm. The threshold of limitation and the amplitude depend on the size of the
9 l3 j; a: f$ I! y2 w' J; [( L3 Iparticles. The rise of the optical limiting effect is measured by picosecond laser spectroscopy. For the largest
, b" B; }  K6 p" e( |+ V5 E5 F. Eparticles, it lasts 1 ns. The limitation effect is attributed to large light-scattering centers induced by the pulse
around the initial particles.