The results show that the stabe region of the optical tweezer depends on the nonlinear coefficient of refractive index. Moreover, the stable region could be brokendown with a critical value of the nonlinear coefficient of refractive index of the surrounding medium irradiated by Gaussian laser pulse described by given parameters as intensity, duration and radius of beam waist. | Communications in Physics, Vol. 23, No. 2 (2013), pp. 155-161 THE INFLUENCE OF THE SELF-FOCUSING EFFECT ON THE OPTICAL FORCE ACTING ON DIELECTRIC PARTICLE EMBEDDED IN KERR MEDIUM HOANG VAN NAM Council of Science and Technology, Ha Tinh, Vietnam CAO THANH LE Ha Tinh University No. 447, 26/3 Road, Dai Nai, Ha Tinh City, Ha Tinh, Vietnam HO QUANG QUY Academy of Military Science and Technology 17 Hoang Sam Street, Nghia Do, Cau Giay, Hanoi, Vietnam Received 30 January 2013; revised manuscript received 31 May 2013 Accepted for publication 10 April 2013 Abstract. The influence of the self-focusing effect arised from Kerr effect on the optical force acting on the dielecric particle embedded in the Kerr medium, which is irradiated by the Gaussian beam, is proposed to concern. The expressions of the optical forces with the nonlinear refractive index and nonlinear focal length are derived. Using them, the distribution of the optical forces in the trapping region of the optical tweezer is simulated and discussed for same distinguished case of the Kerr medium with different nonlinear coefficients. The results show that the stabe region of the optical tweezer depends on the nonlinear coefficient of refractive index. Moreover, the stable region could be brokendown with a critical value of the nonlinear coefficient of refractive index of the surrounding medium irradiated by Gaussian laser pulse described by given parameters as intensity, duration and radius of beam waist. I. INTRODUCTION The optical tweezer used CW laser beam is used to trap the micro dielectric particle, which is embedded in a medium as gas, fluid [1-8]. Up to now, the optical trap using pulsed Gaussian beam and the optical trap using counter-propagating pulsed Gaussian beams has been paid attention to trap the nanoparticle [9-11]. Unfotunately, in the mentioned works, there was attention to thermal effect of the medium only (the Brownian motion), but not to other effect as random or Kerr. In work [12], the .
