Linear and nonlinear optical response of aligned gold nanorods Lazaro A. Padilha 1 , Jake P. Fontana 2 , Dana Kohlgraf-Owens 1 , Michele F. Moreira 2 , Scott Webster 1 , Peter Palffy-Muhoray 2 , Pieter G. Kik 1 , David J. Hagan 1 , and Eric W. Van Stryland 1 , 1 College of Optics and Photonics CREOL & FPCE, Univ. of Central Florida, 4000 Central Florida Blvd, Orlando, FL, 32826 2 Liquid Crystal Institute, Kent State University, Kent, OH, 44242 padilha@creol.ucf.edu Abstract: The optical properties of gold nanorods in toluene are studied as a function of orientation by aligning them in a low frequency electric field. Their nonlinear optical response is consistent with a 2-level saturation model. ©2009 Optical Society of America OCIS Code: (160.3918) Metamaterials; (190.4400) Nonlinear optics, materials. 1. Introduction The influence of metal nanoparticles on the linear optical properties of materials has received attention in large part for potential applications in optical metamaterials. There is also considerable interest in the nonlinear optical, NLO, properties of these materials. In this paper we discuss the linear and NLO properties of gold nanorods (NR) suspended in toluene as a function of NR alignment. Polarization-resolved open and closed aperture femtosecond Z-scan is used to study the response for light polarized along and perpendicular to the direction of alignment. The observed changes in the NLO properties before and after alignment correspond to the changes in the material loss consistent with a homogeneously-broadened 2-level model. 2. Results and Discussion Gold NRs were synthesized using a seed-mediated growth method described in Ref. [1] and suspended in toluene. The NRs are aligned horizontally and normal to the optical axis by an externally applied 60Hz, electric field [2, 3]. Figure 1 shows absorption associated with the plasmon resonance for parallel and perpendicular polarizations with respect to the longitudinal NR. The longitudinal peak is suppressed when the electric field is applied and the absorption is measured with light polarized perpendicular to the alignment (90 o ). Conversely, enhancement of this peak is observed when the NRs are aligned perpendicular to the laser propagation direction and parallel to the polarization (0 o ). The optical density changes by ~ 40% when the polarization is changed from 90 o to 0 o for an applied voltage of 11,250 V, corresponding to a field strength of ~ 3-4 V/μm. 400 500 600 700 800 900 0.4 0.8 1.2 1.6 2.0 Linear Absorption Measured with Horizontally Polarized Light 0 V 5000 V 7500 V 11250 V 15000 V Absorption (a.u.) Wavelength (nm) Polarization direction 400 500 600 700 800 900 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Absorption (a.u.) Wavelength (nm) 0 V 7500 V 11250 V 15000 V Linear Absorption Measured with Vertically Polarized Light Polarization direction Fig. 1. Linear absorption as function of the applied field for two cases of light polarized perpendicular to the applied field (left) and along the direction of the applied field (right).