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Optical trapping of the low index of refraction particles by focused vortex beams and two face-to-face focused beams

Duan Meiling, Zhang Hanghang, Li Jinhong

Optica Applicata

2020

Vol. 50, nr 3

447--461

Using the extended Huygens–Fresnel principle and Rayleigh scattering theory, optical trapping of the low index of refraction particles using a focused Gaussian Schell-model (GSM) non-vortex beam, a focused GSM vortex beam, and two face-to-face focused GSM vortex beams have been studied. The results demonstrate that the focused GSM non-vortex beam cannot capture the low index of refraction particles, however, the focused GSM vortex beam can be a two-dimensional trap of particles in the z-axis, and the transverse gradient force Fgrad,x and the trapping equilibrium region increase as the topological charge m increases. As the focal length f or the refractive index of particles np decreases, the radiation forces increase and the trapping ability also enhances. To trap the low index particles in three-dimensional space, we adopt that the two face-to-face focused GSM vortex beams can be used to construct an optical potential well. The transverse gradient force of two face-to-face focused GSM vortex beams is twice that of a single GSM vortex beam. The limit of the radius for the low index of refraction particles that were stably captured has also been determined. The obtained results provide valuable information for trapping and manipulating the low index of refraction particles using GSM vortex beams, which may be applied in micromanipulation, biotechnology, nanotechnology and so on.

Propagation of Gaussian Schell-model vortex beams in biological tissues

Duan Meiling, Tian Yannan, Li Jinhong

Optica Applicata

2019

Vol. 49, nr 2

203--215

The dependence of changes in the relative intensity and the spectral degree of coherence on the refractive-index Cn2 of biological tissues, space correlation length σ0 and wavelength λ of the Gaussian Schell-model (GSM) vortex and non-vortex beams in biological tissues has been studied. It is shown that the intensity distribution of GSM vortex beams passing through the biological tissues undergoes several stages. The bigger Cn2 is, and the smaller σ0 is, the quicker the intensity evolution is. The attenuation of intensity for GSM vortex beams is much slower than that of non-vortex beams, thus the beam quality of the former is better than the latter. When propagating through the biological tissue, the phase singularities of GSM vortex beams will appear. As the propagation distance increases, the position of the phase singularities will shift, and these points will disappear where the changes in the spectral degree of coherence of GSM vortex beams are consistent with those of GSM non-vortex beams. At the same propagation distance, the bigger Cn2 is, and the smaller σ0 and λ are, the shorter the distance between the phase singularities and the z axis is, when the propagation distance z is in the range of 0–50 μm.