Abstract
Near-field rotation of a trapped particle under focused evanescent Laguerre-Gaussian beam illumination is theoretically investigated by mapping the two-dimensional transverse trapping efficiency exerting on the particle. It is revealed that the severe focal field deformation associated with a focused evanescent Laguerre-Gaussian beam causes a significant impact on the transverse trapping performance of the microparticle. Compared with the far-field trapping force, strong tangential force components have been observed in the transverse efficiency mapping, which potentially lead to rotational motions to the particle within a small trapping volume in the optical near-field.
Highlights
Optical tweezers have been widely used in the fields of modern physics, chemistry and biology for confinement and manipulation of microparticles, biological cells and molecules [1,2,3,4,5]
Near-field trapping using a focused evanescent field generated by a high numerical aperture (NA) total internal reflection (TIR) objective illuminated with an annular beam has been demonstrated to be advantageous over the far-field trapping scheme in biological samples [6,7,8,9], and in particular the red blood cells [9]
It has been revealed recently that when the LG beams are combined with the focused evanescent field, an anomalous focal field deformation occurs due to the phase dislocation induced by TIR and the helical phase front of the LG beams [17]
Summary
Optical tweezers have been widely used in the fields of modern physics, chemistry and biology for confinement and manipulation of microparticles, biological cells and molecules [1,2,3,4,5]. Near-field trapping using a focused evanescent field generated by a high numerical aperture (NA) total internal reflection (TIR) objective illuminated with an annular beam has been demonstrated to be advantageous over the far-field trapping scheme in biological samples [6,7,8,9], and in particular the red blood cells [9] This is due to a significantly reduced focal volume, which can substantially suppress the background and the heating effect [3, 6,7,8,9,10,11]. The rotational motion is examined by mapping the two-dimensional (2D) transverse force exerting on a polystyrene particle
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