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1

Focus shaping of Weierstrass solid immersion lens by an axisymmetric Bessel-modulated Gaussian beam

Dong X., Geng T., Zhuang S.

Optica Applicata

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2013

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Vol. 43, nr 2

s. 247--259

EN

Weierstrass solid immersion lens (SIL) has been used to obtain superresolution because a smaller focal size is desirable. In this paper, focus shaping of Weierstrass SIL illuminated by an axisymmetric Bessel-modulated Gaussian beam (QBG beam) is investigated. It has been found theoretically that the sharper focusing of Weierstrass SIL disappears for a certain beam order of QBG beam. For case of a smaller beam order, the focus still locates on the plane of Weierstrass SIL and Weierstrass SIL still plays a tighter focusing role. However, when the beam order increases continuously, the focus lefts the plane of Weierstrass SIL, and shifts along an optical axis considerably. In addition, under condition of the higher beam order, the dependence of the focal shift on the beam order is nearly linear, which may be used to alter a focal position conveniently.

2

Focus shaping of the radially polarized Bessel–Gauss beam with a sine-azimuthal variation wavefront

Gao X, Zhang D., Mei T., Fu R., Zhuang S.

Optica Applicata

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2013

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Vol. 43, nr 3

567--582

EN

Focusing properties of the radially polarized Bessel–Gauss beam with a sine-azimuthal variation wavefront was investigated by the vector diffraction theory. The wavefront distribution is the sine function of the azimuthal angle with one phase parameter that indicates the phase change frequency. Results show that the focal pattern can be altered by the phase parameter, and many novel focal patterns may occur, such as multiple dark-foci focal pattern, crescent shape, and wheel shape. For case of a higher phase beam, the whole focal pattern turns on a symmetric wheel shape with multiple reduplicate intensity elements. When the phase parameter is an odd number, the number of reduplicate elements equals the phase parameter, while when the phase parameter is an even number, the number of reduplicate elements is two times the phase parameter. In addition, the effect of the phase parameter on the focal pattern is more considerable than that of the beam parameter under low numerical aperture. Under higher numerical aperture, the effect of the beam parameter on the focal pattern gets stronger.

3

Focus shaping of Bessel-Gauss beam with radial varying polarization

Gao X., Fu R., Shen H., Dong X., Geng T., Zhuang S.

Optica Applicata

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2012

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Vol. 42, nr 3

481-491

EN

Focusing properties of Bessel-Gauss beam with radial varying polarization are investigated based on vector diffraction theory in this article. The polarization angle formed by polarization direction and radial coordinate is the function of the radial distance in pupil plane, and one polarization parameter indicates the speed of change of polarization angle. It was found that the intensity distribution in focal region can be altered considerably by the beam parameter and polarization parameter. For a small beam parameter, the focal spot broadens transversely, distorts into ring focus, and then evolves back into focal spot on increasing polarization parameter. When beam parameter gets higher, focal pattern becomes complicated and the focus evolution principle with increasing beam parameter also changes significantly. Some novel focal patterns may appear, including multiple intensity rings, dark hollow focus, cylindrical crust focus.

4

Conditions for tighter focusing and higher focal depth of radially polarized vector beam

Gao X, Wang Q, Yun M, Yu J, Guo H, Zhuang S

Optica Applicata

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2012

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Vol. 42, nr 1

85--101

EN

The radially polarized vector beam has attracted much attention recently and was also used to obtain a smaller focal spot. In this paper, highly focusing properties of radially polarized vector beam are investigated by comparing them with those of linearly polarized beam. A condition was found for tighter focusing of radially polarized vector beam. The focal spot of radially polarized vector beam is not always smaller than that of linearly polarized beam. Even if only a longitudinal field component is considered, in fact, the condition for tighter focusing of radially polarized vector beam is very complicated. Therefore, more attention should be paid to the smaller focal spot generation by means of radially polarized vector beam in practical use. In addition, the focal depth of radially polarized beam decreases on increasing numerical aperture under condition of small radius ratio, and increases on increasing radius ratio. The focal depth difference between these two kinds of beams shrinks upon increasing radius ratio and numerical aperture.

5

High focusing of radially polarized Bessel-modulated Gaussian beam

Gao X., Gao M., Hu S., Guo H., Wang J., Zhuang S.

Optica Applicata

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2010

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Vol. 40, nr 4

965--974

EN

The focusing properties of radially polarized Bessel-modulated Gaussian (QBG) beam are theoretically investigated in detail by vector diffraction theory. The QBG beam contains an optical vortex. Calculation results show that the intensity distribution in focal region of radially polarized QBG beam can be altered considerably by changing beam parameter and the topological charge of the optical vortex. Beam parameter can induce remarkable focus evolution in axial direction. While topological charge adjusts intensity distribution more significantly in transverse direction, for instance, one focal spot changes into one ring pattern. And some novel focal patterns may occur, including two-peak focus, one ring focus, two-ring focus, three-ring focus, and even dark hollow focus, which is very important in optical tweezers technique.