Optical trapping of metallic Rayleigh particles by using coherently and incoherently combined beams

Abstract

The effect of two beam combination schemes, i.e. combination of coherent and incoherent beam, on the radiation force and stability in trapping metallic Rayleigh particles is studied, where the dependences of the radiation force on beam combination scheme, off-axis distance, coherence parameter and particle radius are stressed and illustrated by numerical examples. It is shown that there exist critical values dc and c for different combination schemes. For 0ddc or 0cthe Gaussianthe Gaussian-like intensity profile takes place in the geometrical focal plane, so that the transverse gradient force can act as a restoration force to provide stable equilibrium point. Fordd0,c or00,cthe transverse gradient force can not trap metallic Rayleigh particles. For 0ddc the intensity, the radiation force, the trapping stiffness, and the longitudinal trapping range of coherently combined beam are larger than those of incoherently combined beams. Therefore, a suitable choice of combination scheme, smaller off-axis distance and coherence parameter is beneficial to trapping metallic Rayleigh particles in the use of combined beams.