arXiv subjects

Mousumi Upadhyay Kahaly

Publications and source records attributed to Mousumi Upadhyay Kahaly.

6 recordsLinked to original sources

arXiv2026

Harnessing Machine Learning for Ultrafast Science in Facility Settings: Opportunities and Challenges

Ultrafast science is rapidly evolving from a collection of specialized laser experiments into a facility-scale, data-intensive research endeavour. High-repetition-rate femtosecond and attosecond sources, synchronized multidimensional diagnostics, and increasingly nonlinear laser-matter interactions now generate heterogeneous data streams whose volume, speed, and complexity often exceed the capacity of conventional manual workflows. This chapter examines how machine learning can become an enabling layer for next-generation ultrafast facilities, with emphasis on the Extreme Light Infrastructure (ELI) ecosystem. We discuss the scientific drivers for artificial-intelligence-assisted experimentation, propose a facility-scale digital architecture spanning acquisition, ingestion, storage, analytics, machine learning, adaptive feedback, and user interfaces, and review representative examples from ELI ALPS, ELI Beamlines, and ELI-NP. The central thesis is that machine learning should not be treated merely as an offline data-analysis tool; rather, when constrained by physical insight and embedded in robust data infrastructure, it can support real-time diagnostics, surrogate modeling, anomaly detection, experimental optimization, and progressively autonomous discovery workflows.

physics.optics↗

arXiv2026

Highly Efficient Second/Third Harmonic Generation in van der Waals Layered Material AgScP2S6 with Anisotropic Polarization and Temperature Dependence

Single-crystal X-ray diffraction and nonlinear optical measurements, especially second- and third-harmonic generation (SHG/THG) are comprehensively investigated for the van der Waals layered material AgScP2S6 with a non-centrosymmetric P31c (159) space group. Linear optical constants are extracted using spectroscopic ellipsometry and applied in fitting the harmonic generation behavior. Polarization-resolved SHG and THG measurements exhibit pronounced anisotropy, with emission patterns well-described by theoretical models derived from the khi(2) and khi(3) tensor elements. The material demonstrates exceptionally high nonlinear susceptibilities, with khi(2) ~ 10^(-8) m/V and khi(3) ~ 10^(-17) m^2/V^2 which is a few orders of magnitude greater than comparable 2D materials reported in the literature. Temperature-dependent SHG and THG measurements from 300 K to 25 K reveal exponential decay in harmonic signal intensities, attributed to reduced carrier mobility, with no evidence of structural phase transitions, consistent with results from single crystal diffraction and heat capacity measurements. Polarization-resolved SHG and THG measurements also reveal distinct orientation and ellipticity trends, highlighting the anisotropic nonlinear tensor contributions and contrasting polarization selection rules in the material. These results establish AgScP2S6 as a high-performance, thermally stable, and highly anisotropic nonlinear candidate material suitable for compact photonic applications such as ultrafast optical modulators, polarization-sensitive detectors, and wavelength-tunable light sources.

cond-mat.mtrl-sci↗

arXiv2024

MIR laser CEP estimation using machine learning concepts in bulk high harmonic generation

Monitoring the carrier-envelope phase (CEP) is of paramount importance for experiments involving few cycle intense laser fields. Common measurement techniques include f-2f interferometry or stereo-ATI setups. These approaches are adequate, but are challenging to implement on demand, at different locations as additional metrology tools, in intense few cycle laser-matter interaction experiments, such as those prevalent in sophisticated user beamlines. In addition there are inherent difficulties for CEP measured at non-conventional laser wavelengths (like e.g. mid infrared) and measurements above 10 kHz laser repetition rates, on single shot basis. Here we demonstrate both by simulations and by experiments a machine learning (ML) driven method for CEP estimation in the mid infrared, which is readily generalizable for any laser wavelength and possibly up to MHz repetition rates. The concept relies on the observation of the spectrum of high harmonic generation (HHG) in bulk material and the use of ML techniques to estimate the CEP of the laser. Once the ML model is trained, the method provides a way for cheap and compact real-time CEP tagging. This technique can complement the otherwise sophisticated monitoring of CEP, and is able to capture the complex correlation between the CEP and the observable HHG spectra.

physics.optics↗

arXiv2024

Controlling high-harmonic generation from strain engineered monolayer phosphorene

Phosphorene, a well-studied 2D allotrope of phosphorus, features unique properties such as widely tunable bandgap, high carrier mobility, and remarkable intrinsic in-plane anisotropy. Utilizing these structural and electronic properties, we investigate ultrafast electron dynamics and high harmonic generation (HHG) from phosphorene subject to band structure engineering through external strain, based on ab initio time-dependent density-functional theory approach. We show that strong field processes in such systems can be optimized and controlled by biaxial tensile and compressive strain engineering, that results in electronic structure modification. While -10% strain resulted in closing of band gap, 2% strain increased the gap by 22% with respect to 0.9 eV in pristine phosphorene, consequently affecting the high harmonic yield. With reduction of gap, by applying strain from 2% to -10%, the valence band near $Γ-$point becomes more flat and discreet, resulting in large electronic density of states and enhanced electronic excitation, which reflects in their ultrafast sub-cycle dynamics under laser excitation. Moreover, due to its intrinsic in-plane anisotropy, harmonic yield with laser polarization along the armchair (AC) direction is found to be higher than that of the zigzag (ZZ) direction for all the strain cases. Nearly, an order of magnitude enhancement of harmonic intensity is achieved for -10% strain along AC direction. The current study expands the research possibilities of phosphorene into a previously unexplored domain, indicating its potential for future utilization in extreme-ultraviolet and attosecond nanophotonics, and also for efficient table-top HHG sources.

cond-mat.mtrl-sci↗

arXiv2023

Tunable ultrafast thermionic emission from femtosecond-laser hot spot on a metal surface: role of laser polarization and angle of incidence

Ultrafast laser induced thermionic emission from metal surfaces has several applications. Here, we investigate the role of laser polarization and angle of incidence on the ultrafast thermionic emission process from laser driven gold coated glass surface. The spatio-temporal evolution of electron and lattice temperatures are obtained using an improved three-dimensional (3D) two-temperature model (TTM) which takes into account the 3D laser pulse profile focused obliquely onto the surface. The associated thermionic emission features are described through modified Richardson-Dushman equation, including dynamic space charge effects and are included self-consistently in our numerical approach. We show that temperature dependent reflectivity influences laser energy absorption. The resulting peak electron temperature on the metal surface monotonically increases with angle of incidence for P polarization, while for S polarization it shows opposite trend. We observe that thermionic emission duration shows strong dependence on angle of incidence and contrasting polarization dependent behaviour. The duration of thermionic current shows strong correlation to the intrinsic electron-lattice thermalization time, in a fluence regime well below the damage threshold of gold. The observations and insights have important consequences in designing ultrafast thermionic emitters based on a metal based architecture.

physics.optics↗

arXiv2021

A quantum-chemical perspective on the laser-induced alignment and orientation dynamics of the CH$_3$X (X = F, Cl, Br, I) molecules

The laser-induced alignment-and-orientation (A&O) dynamics of the prolate symmetric top CH$_3$X (X = F, Cl, Br, I) molecules is investigated, with particular emphasis on the effect of halogen substitution on the rotational constants, dipole moments, and polarizabilities of these species, as these quantities determine the A&O dynamics. Insight into possible control schemes for preferred A&O dynamics of halogenated molecules and best practices for A&O simulations are provided, as well. It is shown that for accurate A&O-dynamics simulations it is necessary to employ large basis sets and high levels of electron correlation when computing the rotational constants, dipole moments, and polarizabilities. The benchmark-quality values of these molecular parameters, corresponding to the equilibrium, as well as the vibrationally averaged structures are obtained with the help of the focal-point analysis (FPA) technique and explicit electronic-structure computations utilizing the gold-standard CCSD(T) approach, basis sets up to quintuple-zeta quality, core-correlation contributions and, in particular, relativistic effects for CH$_3$Br and CH$_3$I. It is shown that the different A&O behavior of the CH$_3$X molecules in the optical regime is mostly caused by the differences in their polarizability anisotropy, in other terms, the size of the halogen atom. In contrast, the A&O dynamics of the CH$_3$X series induced by an intense few-cycle THz pulse is mostly governed by changes in the rotational constants, due to the similar dipole moments of the CH$_3$X molecules. The A&O dynamics is most sensitive to the $B$ rotational constant: even the difference between its equilibrium and vibrationally-averaged values results in noticeably different A&O dynamics. The contribution of rotational states having different symmetry, weighted by nuclear-spin statistics, to the A&O dynamics is also studied.

physics.chem-ph↗