Rayleigh scattering correlation spectroscopy on diffusion dynamics of nanoparticles under intense laser irradiation Ping-Yu Hee a , Takayuki Uwada* b , Kazunori Okano a , Atsushi Miura a , Hiroshi Masuhara* a a Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan; b Department of Chemistry, Josai University, Sakado, 350-0295, Japan ABSTRACT Rayleigh scattering correlation microspectroscopy is developed and applied to study diffusion dynamics of some nanospheres in water. It was clearly found that the diffusion constant of gold nanoparticles decreased with increasing excitation laser power at the excitation wavelength of higher absorption cross section. This behavior was explained in terms of a coupling between laser trapping by the scattering excitation laser itself and laser heating of the particle. In the case of non-absorbing nanospheres such as silica and polystyrene, the excitation power dependence can be ascribed only to the laser trapping. Experimental setup is introduced, theoretical formulation is described, and future development of this measurement is considered. Keywords: Rayleigh scattering, correlation spectroscopy, gold nanoparticles, photothermal heating, laser trapping 1. INTRODUCTION When laser light is tightly focused close to the diffraction limit by using high numerical aperture lens, photon momentum transfer results in formation of three dimensional trapping potential, exerting photon pressure on small targets. Utilizing the photon force, optical tweezers methods have been developed and laser trapping phenomena have been elucidated 1 . In the past few decades, a tremendous amounts of papers have been published on trapping and manipulating micrometer-sized objects from polymer particle to biological applications 2 , 3 . Recently, the target of the photon pressure is expanding towards nanomaterial and small molecules 3 . When the photon pressure potential is sufficiently larger than the thermal energy of the nanomaterials, they can be trapped stably at the focus. The depth of the photon pressure potential is determined by polarizability of the trapped material and laser power. The polarizability of such nanomaterial is roughly linear to the volume, so that combination of intense laser light with a high numerical aperture lens becomes more essential for nanomaterial to overcome the thermal energy. In this size region, a number of nanomaterials can be trapped in a single _________________________________________________________________________________________________________ *Emails; uwada@josai.ac.jp (TU), masuhara@masuhara.jp (HM) Phone +81-049-271-7996, Fax +81-049-271-7985 (TU) Phone +886-3-571-2121 ext. 56593, Fax +886-3-571-2121 ext. 56593 (HM) Optical Trapping and Optical Micromanipulation X, edited by Kishan Dholakia, Gabriel C. Spalding, Proc. of SPIE Vol. 8810, 88102T · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2023022 Proc. of SPIE Vol. 8810 88102T-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/27/2014 Terms of Use: http://spiedl.org/terms