arXiv subjects

Bikash K. Das

Publications and source records attributed to Bikash K. Das.

4 recordsLinked to original sources

arXiv2026

Single photon zeptosecond interferometry

We demonstrate the generation of a train of attosecond XUV pulses that are in a superposition of wavefront states. Such superposition yields a high precision, self-referencing, common path XUV interferometer setup to produce pairs of spatially separated and independently controllable XUV pulses that are locked in phase and time with a temporal jitter of 3.5 zs (zs = zeptoseconds = $10^{-21}$). In our approach, we can independently control the relative phase/delay of the two optical beams with a resolution of 52 zs. Since the jitter is on the order of the Compton time scale, we explore the level of correlation between the non-local photons by comparing different spatial mode superpositions. Further, thanks to the stability of the interferometer we can retrieve the interference pattern through photon counting. Through post-selection of different particle events we can analyze one, two or more photon events. We argue that this zeptosecond level of temporal precision will open the door for new dynamical QED tests at lower intensities while photon counting experiments can also have an impact on the emerging field of quantum light in strong fields. We also discuss the potential impact on other areas, such as time-dependent QED, imaging, measurements of non-locality, and molecular quantum tomography.

physics.optics↗

arXiv2025

Optical Vortices: Revolutionizing the field of linear and nonlinear optics

Light is the fundamental medium through which we perceive the world around us. In the modern era, light can not only be used in its raw form but can also be used as a versatile tool. Generally, light fields carry energy and momentum (both linear and angular). Due to the transfer of linear momentum from light to matter, the radiation pressure is exerted, whereas, the intrinsic spin angular momentum (SAM) is associated with the polarization states of light. Light fields embedded with optical orbital angular momentum (OAM) -- also known as optical vortices or phase singular beams -- have truly revolutionized the field of optics and extended our basic understanding of the light-matter interaction process across various scales. Optical vortices -- spatially characterized by the presence of twisted phase fronts and a central intensity null -- have found a myriad of applications starting from microparticle trapping and manipulation to microscopy, optical communication, and quantum information science, among others. Here, we revisit some of the fundamental concepts on optical vortices and discuss extensively on how this new dimension of light i.e., the OAM, has been exploited in both linear and nonlinear optical regimes. We discuss the different types of vortex beams, the techniques used to generate and detect their OAM, and their propagation. Particularly, we put a special emphasis on the utilization of vortex beams in nonlinear regimes to explain different optical phenomena such as the second harmonic generation, parametric down-conversion, and high-order harmonic generation. The generation of vortex beams in the UV to XUV regimes, encoded with higher OAM values, could potentially extend their application range to areas such as high-capacity data transmission, stimulated emission depletion microscopy, phase-contrast imaging, and particle trapping in optical tweezers, among others.

physics.optics↗

arXiv2025

The role of spatiotemporal couplings in harmonic vortex generation

We explore the impact of spatiotemporal couplings (STCs) on high-order harmonic generation (HHG) driven by spatiotemporal vortex beams. Our investigation demonstrates how STCs shape key properties of the generated harmonic beams, including their intensity distribution and different chirps. By analyzing these chirps, we establish a clear connection between STCs and the observed harmonic structures. Furthermore, we examine the HHG process in both the near- and far-fields, identifying the conditions under which these perspectives align and provide consistent results. By clarifying the role of spatiotemporal vortex beams in HHG, this work contributes to a broader understanding of the interplay between spatiotemporal effects and harmonic generation, while offering a framework to merge differing interpretations in the literature.

physics.atom-ph↗

arXiv2024

Interference of high-order perfect optical vortex beams

We investigate the interference of high-order perfect optical vortex (POV) beams with different topological charges. Through numerical simulations, we reveal a remarkable phenomenon: keeping the beam width, and beam radius fixed while changing the topological charge, the splitting of the composite POV beam into two distinct individual perfect vortices occurs exactly at the same inter-axial separation. The observed interference pattern exhibits pronounced sensitivity to factors such as axial separation, phase shift, beam radius, and topological charges of the constituent beams. Notably, our findings are contrasted with the interference of high-order Laguerre-Gauss (LG) beams, highlighting that the splitting of composite vortices into their individual components is more rapid in the case of LG beams. Our research provides significant insights into the distinct interference properties of high-order POV beams, presenting potential applications in the fields of optical manipulation and communication systems.

physics.optics↗