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Optical trapping forces of focused circular partially coherent beams on Rayleigh particles

Yu Chaoqun, Chen Fuchang, Zeng Jun, Huang Cheng, He Zhimin, Lin Huichuan, Zhang Yongtao, Chen Ziyang, Pu Jixiong

Optica Applicata

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2022

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Vol. 52, nr 4

575--583

EN

The optical trapping forces of tightly-focused radially polarized circular partially coherent beams on Rayleigh particles are theoretically investigated. Numerical calculations are performed to study the optical trapping forces on Rayleigh particles for different initial coherent length of the incident circular partially coherent beams. The results show that the magnitude of the gradient force decreases with the reduction of the initial coherent length of the focused radially polarized circular partially coherent beams, while the balanced position (i.e., the position where the optical trapping forces becomes zero) stays constant. Moreover, the focused spot gradually elongates along the optical axis with the reduction of the initial coherent length, and the axial gradient force on Rayleigh particles also decreases gradually with the reduction of the intensity gradient in axial direction. As there exists an spherical aberrant in the focusing optical system, the focal spot in the direction of the optical axis becomes trumpet-shaped, and the optical trapping forces on Rayleigh particles change as well.

2

Q-switched partially coherent lasers with controllable spatial coherence

Wang Yushuang, Ji Xuanxuan, Chen Ziyang, Pu Jixiong

Optica Applicata

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2021

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Vol. 51, nr 2

245--256

EN

We develop a Q-switched degenerate laser, delivering a partially coherent light pulse of duration about 16 ns. The spatial coherence of the output laser pulse can be varied by tuning the spatial filter inside the laser resonator, and the oscillating transverse mode structure can be determined by measuring the degree of coherence of the output laser pulse. It is shown that the larger is the diameter of the spatial filter, the more are the oscillating transverse modes, and the lower is the degree of coherence. Based on coherent-mode representation for the partially coherent source, we can estimate the transverse mode contribution to the output partially coherent laser. The experimental results on suppressing speckle demonstrate that the generated partially coherent light possesses the characteristics of rapid reduction of spatial coherence, making it an ideal source for high-speed imaging and ranging applications.

3

Generation of optical needle and dark channel by tight focusing of radially polarized circular partially coherent beams

Lin Huichuan, Li Yan, Zhou Xiaoming, Wang Juanjuan, Chen Ziyang, Pu Jixiong

Optica Applicata

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2020

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Vol. 50, nr 2

229--240

EN

We theoretically investigate the tight focusing of radially polarized circular partially coherent(RPCPC) beams through a high numerical aperture objective. The sub-wavelength super-long optical needle and dark channel can be obtained near the focus, by engineering the source coherent length of the incident RPCPC beams. The length of the optical needle and the dark channel can be adjusted, and the obtained maximal lengths of the optical needle and the dark channel are both 22λ.The full width at half maximum of the optical needle and the dark channel are 0.6λ and 0.48λ, respectively.