Structured light beams

Structured laser beams are a type of laser beam that exhibit spatially structured amplitude, phase, or polarization. They are designed to maintain low divergence and can propagate over long distances while preserving their intensity profile. Key features include:

Publications:

Tripathi K, Kumar R, Kumar P, Polarization-referenced phase modulation for encoding and detection of structured singular beams, Appl. Phys. B 2025.

Vector-vortex laser beams

Singular optics is a branch of physics studying light fields with localized, topological singularities, such as phase dislocations (optical vortices) and polarization singularities. Unlike traditional optics, it focuses on structured, non-smooth wave fronts where intensity is zero and phase is undefined. Key applications include optical manipulation, imaging, and communications. 

Publications:

Laxminarayan, Nishchal NK, Omatsu T, Rao, Kumar P, “Singularity transformation through single-pass phase modulation of light” Sci Rep. 2025,  https://doi.org/10.1038/s41598-025-90451-z

Kumar P, Rao AS, Omatsu T, “Generation of V-point polarization singularity using single phase encoding with a spatial light modulator” Sci Rep. 2023, 13 (1), 1-7, https://doi.org/10.1038/s41598-022-27337-x

Kumar P, Nishchal NK, Omatsu T, Rao AS, “Self-referenced interferometry for single-shot detection of vector-vortex beams,” Sci Rep. 2022, 12, 1-11,  https://doi.org/10.1038/s41598-022-21485-w

Optical Skyrmions

Optical skyrmions are robust, topological quasiparticles of light with swirling polarization or phase patterns, acting as "photonic, topological textures" that remain stable even when disturbed. Formed by structuring light's, polarization, these 3D vector fields (often called Stokes skyrmions) are promising for ultra-high-density optical communication, computing, and information storage. 

Publications:

Laxminarayan, Tripathi KK, Kumar P, Rao AS, and Omatsu T, "Single-phase modulated optical skyrmions for information security applications," Opt. Express 33, 51116-51141 (2025). https://doi.org/10.1364/OE.573686

Spatial light modulators for beam shaping

A Spatial Light Modulator (SLM) is a, typically computer-controlled, optoelectronic device that modulates the intensity, phase, or polarization of light across a 2D surface. Commonly based on Liquid Crystal on Silicon (LCoS) or Liquid Crystal Display (LCD) technology, SLMs enable real-time wavefront shaping for applications like holographic displays, optical tweezers, laser beam shaping, and fiber communication. 

Publications:

Tripathi K, Shina G, Dixit A, Kumar P. Generation of cylindrical-vector beams using a dual, slow-axis liquid crystal Spatial Light Modulator, IEEE Photon. Technol. Lett. 2025.

Kumar P, Nishchal NK, "Formation of singular light fields using phase calibrated spatial light modulator" Opt. Lasers Eng. 2021, 146, 106720. https://doi.org/10.1016/j.optlaseng.2021.106720

Kumar P, Nishchal NK, "Phase response optimization of a liquid crystal spatial light modulator with partially coherent light" Appl. Opt. 2021, 60, 10795-10801. https://doi.org/10.1364/AO.439654

Interferometry

Interferometry is a technique that utilizes the principle of superposition to combine waves, allowing for the analysis of their interference patterns. It is widely used in various fields of science and engineering, including optical, infrared, and radio astronomy. Interferometers work by merging light sources to create measurable interference patterns, which can provide diagnostic information about the original waves.

Publications:

Kumar P, Nishchal NK, Omatsu T, Rao AS, “Self-referenced interferometry for single-shot detection of vector-vortex beams,” Sci Rep. 2022, 12, 1-11,  https://doi.org/10.1038/s41598-022-21485-w

Laxminarayan, Kumar P, “Charge identification of composite vortex beams through self-referenced interferometry” Opt. Commun. 2025, https://doi.org/10.1016/j.optcom.2025.131625

Optical Cryptography

Optical cryptography refers to the use of optical technologies to perform cryptographic functions, which traditionally rely on electronic circuits. This innovative approach aims to leverage the properties of light to enhance data security, particularly in high-speed networks. Unlike conventional encryption methods that process data in binary form using electronic signals, optical cryptography seeks to create new algorithms that operate on the analog nature of light.

Publications:

Kumar P, Fatima A, Nishchal NK, "Arbitrary vector beam encoding using single modulation for information security applications" IEEE Photon. Technol. Lett. 2021 33, 243–246,. https://doi.org/10.1109/LPT.2021.3052571

Shikder A, Kumar P, Nishchal NK, Image encryption by structured phase encoding and its effectiveness in turbulent medium, IEEE Photon. Technol. Lett. 2022, 35, 128-131. https://doi.org/10.1109/LPT.2022.3226200

Structured light for nanofabrication on materials

This work is in collaboration with Prof. Omatsu's group at Chiba University, Japan

Laser material processing involves directing a high-intensity, focused laser beam onto a material to alter its properties or geometry. The laser acts as a non-contact, highly controllable energy source, enabling processes such as cutting, welding, drilling, engraving, and surface modification with minimal mechanical stress on the workpiece. The interaction of laser light with the material depends on absorption, reflection, and transmission, which vary by material type and laser wavelength.

Publications:

Tamura R, Kumar P, Rao AS, Tsuda K, Getzlaff F, Miyamoto K, Litchinitser NM, Omatsu T, “Direct imprint of optical skyrmions in azopolymers as photo-induced relief structures” APL Photonics 2024, https://doi.org/10.1063/5.0192239

Ocular Wavefront sensors

This work is in collaboration with Prof. Yoon's group at University of Houston, USA

Optical wavefront sensors are essential devices used to measure and analyze the shape of light waves. They are integral to various fields, including astronomy, ophthalmology, and laser system optimization. These sensors detect and correct aberrations in optical systems, enhancing image clarity and focus. The Shack-Hartmann Wavefront Sensor (SHWFS) is a common design, where a microlens array focuses light onto a camera sensor, allowing for precise wavefront reconstruction. Wavefront sensors are crucial for applications requiring nanometer-scale precision, where even minor deviations can compromise system performance

Publications:

Bang SP, Kumar P, and Yoon G, "Quantifying ocular microaberration using a high-resolution Shack-Hartmann wavefront sensor," Biomed. Opt. Express, 16, 3128-3138, 2025. https://doi.org/10.1364/BOE.566011

Kumar P, Bang S, Yoon G, Ocular Optics Characterization using Transport of Intensity Equation, Investigative Ophthalmology & Visual Science 64 (8), 5330-5330, June 2023, https://iovs.arvojournals.org/article.aspx?articleid=2789277

Fundus Photography

This work is in collaboration with Vadanya Scientific & AIIMS Raipur

Fundus photography involves photographing the rear of an eye, also known as the fundus. Specialized fundus cameras consisting of an intricate microscope attached to a flash enabled camera are used in fundus photography. The main structures that can be visualized on a fundus photo are the central and peripheral retina, optic disc and macula. Fundus photography can be performed with colored filters, or with specialized dyes including fluorescein and indocyanine green.

Publications:  work in progress...