Abstract
The principle of optical trapping is conventionally based on the interaction of optical fields with linear-induced polarizations. We develop the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate femtosecond laser pulses, based on the linear and nonlinear polarization effects.
Introduction of results
Optical tweezers, also known as optical trapping or optical micro-manipulation, is a useful technique for noncontact and noninvasive manipulation of small particles using a focused laser beam. Thus this technique has wide applications in physics, chemistry, biology, and other disciplines. Up to now, the stable optical trapping of micro- and nano-particles has been extensively demonstrated by the use of a continuous-wave (CW) laser beams.
Recently, the optical trapping technique has been extended by substituting a CW laser with high-repetition-rate femtosecond laser pulses. With the femtosecond laser pulses, several novel phenomena have been observed, including the trapping split behavior in the process of capturing gold nanoparticles, a controllable directional ejection of optically trapped nanoparticles, and the immobilization dynamics of a single polystyrene sphere.
Conventionally, the principle of optical trapping is based on the interaction of optical fields with linear-induced polarizations. In the femtosecond optical trapping, however, the observations indicate that the optical force originating from the nonlinear polarization becomes significant and cannot be neglected if the trapped particles exhibit nonlinear optical effects.
Very recently, Prof. Yiping Cui and Prof. Bing Gu from Southeast University collaborated with both A/P Zhuqing Zhu from Nanjing Normal University and Prof. Qiwen Zhan from University of Dayton (USA) have developed the optical forces of focused femtosecond laser pulses on a nonlinear optical Rayleigh particle.
Based on the linear and nonlinear polarization effects, we investigate both the magnitude and distribution of 3D optical forces of focused femtosecond laser pulses on a nonlinear optical nanoparticle. It is shown that the self-focusing effect enhances the trapping ability, whereas the self-defocusing effect leads to the splitting of the potential well at the focal plane and destabilizes the optical trap. Our results show good agreement with the reported experimental observations and provide theoretical support for capturing nonlinear optical nanoparticles.
This research work entitled “optical forces of focused femtosecond laser pulses on nonlinear optical Rayleigh particles” has been published on Photonics Research.
Paper links：https://www.osapublishing.org/prj/abstract.cfm?uri=prj-6-2-138
