arXiv subjects

Brijesh Kumar Singh

Publications and source records attributed to Brijesh Kumar Singh.

4 recordsLinked to original sources

arXiv2025

Experimental realization of Energy modulation of high-order R-TEM laser modes in Radially polarized cylindrical vector beam

A In this work, an experimental approach is introduced to redistribute optical energy among the multiple concentric core rings of high-order R-TEM laser modes, differing from conventional high-order R-TEM modes that inherently exhibit non-uniform energy across their rings. By employing a diffractive optical element formed from a binary phase mask with two oppositely phased regions, the energy sharing between the rings can be tuned to achieve a variable intensity ratio in the ring pattern. The resulting modulated high-order R-TEM modes are expected to surpass standard R-TEM modes for applications requiring ring structures with nearly equal intensity, such as micro- and nanoparticle manipulation, optical lithography, and near-field optical data storage.

physics.optics↗

arXiv2025

Generation of hallow vector beam by high-order cylindrical vector beams

We propose a method for generating hollow beams using higher-order cylindrical vector modes of the form R-TEMpl, where the radial index p is varied from 1 to 3 while the azimuthal index is fixed at l = 1. It is found that this scheme performs identically under incident illumination with either radial or azimuthal polarization. For this purpose, we use a focusing lens in combination with a diffractive optical element formed by a computer-generated hologram containing multiple alternate opaque and transparent regions. Based on vector diffraction theory, our analysis shows that the multi-zone amplitude mask redistributes the beam energy, thereby leading to the formation of a hollow beam. The proposed method provides control over the beam width which maintains a uniform dark core size after focusing through the various NA lens across all the higher order modes. Further the width of high intensity ring can be tuned by varying the NA of the focusing lens. This study shows that the proposed method is well suited for trapping particles or atoms while avoiding exposure to high central intensity, enabling improved contrast and resolution, facilitating ring-shaped ablation or heating, guiding atoms through dark regions to minimize thermal effects, and supporting information encoding using orbital angular momentum and other advanced optical applications.

physics.optics↗

arXiv2021

Controlled modulation of optical energy in the high order Hermite-Gaussian laser modes

The multiple lobes of high order Hermite-Gaussian (HG) laser modes differ in terms of shape, size, and optical energy distribution. Here, we introduce a generic numerical method that redistributes optical energy among the lobes of high order HG modes such that all the identical low intense lobes become both moderate or high intense lobes and vice-versa, in a controlled manner. Further, the modes which consist of only two types of intensity distribution among its multiple lobes are transformed together into all high intense lobes. Furthermore, in some cases, moderate intense lobes together with high intense lobes become high intense lobes, and moderate intense lobes together with low intense lobes become high intense lobes. Such controlled modulation of optical energy may offer efficient and selective utilization of each lobe of HG modes in most applications like particle manipulation, optical lithography, and the method can be used in other fields like nonlinear frequency conversion and shaping ultrafast optical pulses.

physics.optics↗

arXiv2017

Particle manipulation beyond the diffraction limit using structured super-oscillating light beams

The diffraction limited resolution of light focused by a lens was derived in 1873 by Ernst Abbe. Later in 1952, a method to reach sub-diffraction light spots was proposed by modulating the wavefront of the focused beam. In a related development, super-oscillating functions, i.e. band limited functions that locally oscillate faster than their highest Fourier component, were introduced and experimentally applied for super-resolution microscopy. Up till now, only simple Gaussian-like sub-diffraction spots were used. Here we show that the amplitude and phase profile of these sub-diffraction spots can be arbitrarily controlled. In particular we utilize Hermite-Gauss, Laguerre-Gauss and Airy functions to structure super-oscillating beams with sub-diffraction lobes. These structured beams are then used for high resolution trapping and manipulation of nanometer-sized particles. The trapping potential provides unprecedented localization accuracy and stiffness, significantly exceeding those provided by standard diffraction limited beams.

physics.optics↗