Generation Of Hollow Beam Research Articles

Nonlinear generation of hollow beams in tunable plasmonic nanosuspensions

We experimentally demonstrate that a probe beam at one wavelength, although exhibiting a weak nonlinear response on its own, can be modulated and controlled by a pump beam at another wavelength in plasmonic nanosuspensions, leading to ring-shaped pattern generation. In particular, we show that the probe and pump wavelengths can be interchanged, but the hollow beam patterns appear only in the probe beam, thanks to the gold nanosuspensions that exhibit a strong nonlinear response to pump beam illumination at the plasmonic resonant frequencies. Colloidal suspensions consisting of either gold nanospheres or gold nanorods are employed as nonlinear media, which give rise to refractive index changes and cross-phase modulation between the two beams. We perform a series of experiments to examine the dynamics of hollow beam generation at a fixed probe power as the pump power is varied and find that nonlinear beam shaping has a different power threshold in different nanosuspensions. Our results will enhance the understanding of nonlinear light–matter interactions in plasmonic nanosuspensions, which may be useful for applications in controlling light by light and in optical limiting.

Generation of hollow beams by using phase filtering with multi-distance phase retrieval

We propose a method to generate beams according to transmission limitation condition by using the multi-distance phase retrieval algorithm. Propagation properties of hollow beams were determined by several intensity patterns along the travel axis. Predicted beams were obtained using a two-step phase filtering from a Gaussian beam with fundamental mode. An iterative phase retrieval method was employed for calculating the phase distribution in the filtering mask. This beam generation approach matched special propagation characteristics of the beams in practical applications.

Gyrator transform of Gaussian beams with phase difference and generation of hollow beam

The optical expression of Gaussian beams with phase difference, which is caused by gyrator transform (GT), has been obtained. The intensity and phase distribution of transform Gaussian beams are analyzed. It is found that the circular hollow vortex beam can be obtained by overlapping two GT Gaussian beams with π phase difference. The effect of parameters on the intensity and phase distributions of the hollow vortex beam are discussed. The results show that the shape of intensity distribution is significantly influenced by GT angle α and propagation distance z. The size of the hollow vortex beam can be adjusted by waist width ω0. Compared with previously reported results, the work shows that the hollow vortex beam can be obtained without any model conversion of the light source.

Three-dimensional phase transformation by impedance-matched dielectric slabs and generation of hollow beams based on transformation optics

We propose a three-dimensional (3D) phase transformation method by an impedance-matched dielectric slab and apply it to generating hollow beams. We first employ transformation optics to establish a method for the transformation between two arbitrary 3D wavefronts through a flat dielectric and impedance-matched material. Then the method is used to convert a solid beam into a hollow beam with desired wavefront. By tuning the transformation surface, different hollow beams can be produced. The results are further validated by 3D finite-difference time-domain simulations.

基于泵浦脉冲诱导等离子体通道的空心光束产生

基于泵浦脉冲诱导等离子体通道的空心光束产生

Generation of hollow beam with radially polarized vortex beam and complex amplitude filter.

The generation of hollow beams with a long focal depth from a radially polarized Bessel-Gaussian beam with a second-order vortex phase and an amplitude filter is theoretically investigated by Richards-Wolf's integral. The null intensity on the optical axis is achieved by introducing the second-order vortex. The long focal depth is a result of the amplitude filtering based on the cosine function and Euler transformation. Numerical results indicate that the focal depth of a hollow beam is improved from 0.96λ to 2.28λ with a slight increase of the transverse size for the simplest amplitude filter design. The intensity distribution twist phenomenon of the x- and y-polarized components around the optical axis due to the introducing of the vortex phase is also discussed. It is believed that the proposed scheme can be used to achieve particle acceleration and optical trapping.

Generation of hollow beam from photonic crystal fiber with an azimuthally polarized mode

A kind of photonic crystal fiber (PCF) with an azimuthally polarized (TE01) mode is proposed to generate hollow beam (HB). The finite element method (FEM) is employed to study the polarization properties of the fiber and normalized intensity of the HB. Simulation results show that the TE01 mode with a low confinement loss in this kind of fiber can provide a high quality HB. By varying arrangement of air holes in the cladding region or changing structure parameters of the PCF, HB of different sizes can be obtained. The smallest dark spot size (DSS) and the narrowest width of HB achieved are about 1μm and 1.4μm at a wavelength of 1.55μm, respectively. This kind of PCF, which can generate HB with an azimuthally polarized mode, has great significance in the technique of optical tweezers.

Generation of hollow beams by spiral rays in multimode light guides

The generation of hollow beams by a multimode light guiding device is analyzed. The light propagation through the light guide is simulated by ray tracing. It is shown that hollow beams are generated by light rays that propagate along a spiral path through the light guide. The properties of the hollow beam depend on the tilt angle and location of the input beam on the front surface of the light guide. The properties of the output beam are investigated experimentally.

Generation of hollow beams by using a binary spatial light modulator

We demonstrate the generation of hollow laser beams by using a binary spatial light modulator and compare the results with those for a continuous modulator. The binary phase modulator produces beams that have continuous, azimuthally varying phase profiles and can be dynamically changed with kilohertz refresh rates. The intensity and phase profiles are recorded through the focus of an imaging lens and are compared with scalar diffraction theory. We highlight properties of the beams relevant to optical dipole traps.