Orbital Angular Momentum Of Vortex Beam Research Articles

Highly efficient detection of near-infrared optical vortex modes with frequency upconversion.

Vortex beams carrying orbital angular momentum (OAM) have been widely applied in optical manipulations, optical micromachining, and high-capacity optical communications. Vortex mode detection is very important in various applications. However, the detection of near-infrared vortex modes is still difficult because of the wavelength limitations of the detection device. Here, we present a study on measuring optical near-infrared vortex modes with frequency upconversion, which can convert a near-infrared beam into a visible beam. In our experiment, the optical near-infrared vortex modes can be measured by the number and orientation of the fringes of the second harmonic intensity patterns. The proposed method is a convenient and flexible way to measure the different OAM of vortex beams, which may have potential applications in all kinds of circumstances that vortex modes involve.

Relation of momentum and orbital angular momentum of Gaussian vortex beam with topological charge and their propagation in free space

While the theory of paraxial approximation is applied to the research of momentum and orbital angular momentum (OAM), the analytical expressions of momentum and OAM of vortex beam are derived. Based on the analytical expression, the distribution and propagation of the momentum and OAM of the Gaussian vortex beam is investigated in free space. Theoretical analysis and numerical simulation show that the values of the radial and angular components of momentum are close to each other, and they are far smaller that the value of the longitudinal component of momentum. The three components of momentum of the beam will expand along the radial direction during propagation in the cross section. The maximum positions of the three components are different, which problem is dependent on the topological charge and the beam width of the source beam. The whole integration results of the three components on the cross section shows the conservation of the momentum of the beam. Besides, the OAM of the Gaussian vortex beam will also expand along the radial direction during propagation. The maximum position of the OAM is the same as that of longitudinal component of the momentum. The whole integration result on the cross section confirms the conservation of the OAM of the Gaussian vortex beam while propagating.

Distribution of phase and orbital angular momentum of tightly focused vortex beams

Based on vectorial Debye theory, the expressions for the distribution of the light field and orbital angular momentum (OAM) of tightly focused vortex beams have been derived. A Bessel-Gaussian (BG) beam is set as the model of the vortex beam. The phase distribution of the field component in the x direction near focus is analyzed as usual by presenting phase contours. It is found that circular edge dislocations exist in the focal plane, but they evolve as screw wavefront dislocations in observation planes away from the focus. Moreover, the dependence of the distribution of phase contours and OAM in the focal plane on the numerical aperture is shown. The distribution of OAM along the z axis is studied; it is found that the optimal location for applications of OAM of vortex beams along the z axis is near the focal plane.