arXiv subjects

Amol R. Holkundkar

Publications and source records attributed to Amol R. Holkundkar.

At least 19 recordsLinked to original sources

arXiv2026

Momentum-space signatures of radial orbital nodes in XUV photoionization

Photoelectron momentum distributions (PMDs) are widely used to probe light matter interactions, yet their angular features are generally assumed to be governed primarily by angular momentum selection rules. We show that the radial structure of the initial bound orbital can qualitatively modify PMD tilt beyond these con- ventional expectations. Using ab-initio time dependent Schrödinger equation calculations, we demonstrate this through comparative studies of single-photon XUV ionization in neon and argon. While neon exhibits a smooth, monotonic increase in PMD tilt with wavelength, argon shows pronounced suppression and reversal near the wavelength where the d wave dipole matrix element passes through a minimum. A partial wave analysis reveals that this non monotonic behaviour originates from a radial node induced minimum in the d wave dipole matrix element, producing a rapid phase jump between interfering s and d wave ionization channels. We further show that atomic interferometric circular dichroism (AICD) provides a sensitive, experimentally accessible probe of this effect.

physics.atom-ph↗

arXiv2026

Coherent control of orthogonal continuum states in XUV photoionization

We demonstrate coherent control of orthogonal continuum electron states in the XUV photoionization of atomic hydrogen using polarization-tailored driving fields. By combining polarization mixing with carrier-envelope-phase (CEP) control, we generate a pair of orthogonal momentum-space basis states whose populations and relative phase can be independently tuned via the polarization-mixing parameter and CEP, respectively. The resulting photoelectron wave packets are prepared as coherent superpositions within this effective two-dimensional subspace, with quantum coherence confirmed by interference visibilities reaching 99% in the photoelectron momentum distributions (PMDs). We further demonstrate that a bichromatic driving-field configuration extends this framework to a four-dimensional continuum manifold, with basis states distinguished by both angular emission patterns and radial momentum distributions, and with independent amplitude and phase control preserved across the higher-dimensional subspace. These results establish that polarization-tailored XUV fields provide a flexible route to independent amplitude and phase control within low-dimensional subspaces of the photoelectron continuum, with the engineered dynamics directly observable in momentum-resolved spectra.

physics.atom-ph↗

arXiv2026

High-harmonic generation as a tunneling delay probe

We investigate the feasibility of using high-harmonic generation (HHG) as a complementary probe of tunneling delay in strong-field ionization. By combining time--frequency analysis of HHG spectra obtained from full time-dependent Schrödinger equation (TDSE) simulations with classical three-step-model (TSM) trajectories, we extract an effective tunneling delay associated with electron motion through the laser-suppressed Coulomb barrier. The analysis is carried out for Hydrogen, Helium, and Argon atoms over a range of laser wavelengths and peak intensities within the tunneling regime. The extracted delay exhibits a systematic dependence on the instantaneous field strength and barrier width at the ionization time, and follows the expected $τ_d \propto 1/\sqrt{I_0}$ scaling consistent with Keldysh--Rutherford-type models and attoclock observations. When recast in terms of the Keldysh parameter, the tunneling delay collapses onto a near-universal trend across different atomic species. While HHG does not provide a direct measurement of tunneling time, the present results demonstrate that it can serve as a robust, internally consistent diagnostic of tunneling dynamics, offering an independent and complementary perspective to established attoclock techniques.

physics.atom-ph↗

arXiv2025

Harmonic emission as a probe to coherent transitions in the topological superconductors

We investigate the dynamical behavior of a topological superconducting system, demonstrating that its static configuration undergoes a transition driven by an intrinsic supercurrent. By analyzing the band population, we confirm the quasiparticle nature of the system both in the presence and absence of an external laser field. Under laser driving, we observe an enhancement in static emission forming a plateau-like structure, accompanied by multiple coherent transitions in the population. These transitions exhibit Rabi-like oscillations, attributed to the presence of Majorana bound states (MBS), further reinforcing the quasiparticle character of the model. Our results highlight the efficacy of laser driving as a probe of the system's topological and dynamical stability.

cond-mat.other↗

arXiv2025

Engineering harmonic emission through spatial modulation in a Kitaev chain

We investigate High-harmonic generation (HHG) in a dimerized Kitaev chain. The dimerization in the model is introduced through a site-dependent modulating potential, determined by a parameter $λ\in [-1:1]$. This parameter also determines the strength of the hopping amplitudes and tunes the system's topology. Depending upon the parameter $λ$, the HHG emission spectrum can be classified into three segments. The first segment exhibits two plateau structures, with the dominant one resulting from transitions to the chiral partner state, consistent with quasiparticle behavior in the topological superconducting phase. The second segment displays multiple plateaus, where intermediate states enable various transition pathways to higher conduction bands. Finally, the third segment presents broader plateaus, indicative of active interband transitions. In the $λ\leq0$ regime, we observe the mid-gap states (MGSs) hybridize with the bulk, suppressing the earlier observed harmonic enhancements. This highlights the key role of the intermediate states, particularly when MGSs are isolated. These results demonstrate that harmonic emission profiles can be selectively controlled through the modulating parameter $λ$, offering new prospects for tailoring HHG in topological systems.

cond-mat.other↗

arXiv2024

Probing topological phase transitions in Aubry-Andre-Harper model via high-harmonic generation

We study the high-harmonic generation in the Aubry-Andre-Harper (AAH) model. The modulating phase of the AAH model is used as a control parameter while preserving the chiral symmetry hosting the zero-energy edge states. The harmonic yield in a particular energy range exhibits a strong dependence on the control parameter with clear separation of the region of topologically trivial and nontrivial phases of the system. The threshold for the harmonic yield is found to serve as an all-optical tool for detecting topological phases. We extended our study with broken chiral symmetry by including the onsite potential. The introduction of the onsite potential lifts the degeneracy in the edge states, which affects the harmonic enhancement. Furthermore, it is also observed that the system's onsite strength can control the HHG yield.

cond-mat.str-el↗

arXiv2024

Role of inter- and intraband current in laser interaction with bi-chromatic quasi-periodic crystals

We study the role of the inter- and intraband current in the laser interaction with the bi-chromatic quasi-periodic crystals. The interaction dynamics are simulated by solving the time-dependent Schrödinger equation in the $k$-space, and time evolution of the inter- and intraband current is obtained in a gauge invariant form. We observed that for certain bi-chromatic potential ratios, the energy band structure of the `valence band' and the `conduction band' facilitate the interband transitions only at the center or at the edge of the Brillouin zone, which leads to a very interesting population transfer mechanism between the bands. The temporal profile of the inter- and intraband current gives a detailed account of the interaction. The higher-order harmonic generation (HHG) is also studied for these bi-chromatic optical lattices, and the resultant harmonic yield is commented upon.

physics.atm-clus↗

arXiv2023

Tailoring polarisation of attosecond pulses via co-rotating bicircular laser fields

The present work introduces a robust way to generate attosecond pulses with tunable ellipticity via high-order harmonic generation by co-rotating $ω- 2ω$ bicircular laser fields. The total electric field of the laser fields exhibits an absence of rotational symmetry, which leads to the generation of high harmonics of the same helicity across a broad range of spectral bandwidth. High-harmonics with the same helicity offer the opportunity to synthesize attosecond pulses with tunable ellipticity. The polarisation properties of the generated harmonics are robust against the variations in driving fields' parameters, such as wavelength, intensity ratio, and the sub-cycle phase between $ω-2ω$ fields. Our work opens an avenue to study chiral-sensitive light-matter ultrafast processes on their intrinsic timescale.

physics.optics↗

arXiv2022

Bi-chromatic driver enabled control of high harmonic generation in atomic targets

We investigated the high-order harmonic generation by interacting time-delayed, linearly polarized bi-chromatic laser pulses with the atomic target. The frequency ratio of secondary to primary fields ($ω_2/ω_1$), along with the relative carrier-envelope-phase (CEP) and respective time-delay between the two pulses, are very instrumental in controlling the ionization of the electron and so the quantum dynamics in continuum. We observed an optimum CEP ($ϕ$) and time delay ($t_d$) for a given bi-chromatic frequency ratio, giving maximum cutoff energy. We studied the effect of CEP and time delay for fixed frequency ratio and observed that the harmonic cutoff could be controlled in an experimentally feasible way. Moreover, the harmonic yield in the energy range 140 eV $-$ 240 eV is also calculated, and it is observed that the harmonic yield scales as $\propto -\sqrtϕ$. The attosecond pulses for different CEP is also calculated by superposing the harmonics in the same energy range, and $\sim 200$ as pulses are observed with peak intensity decreasing with CEP, following the variation of respective harmonic yield with CEP.

physics.atom-ph↗

arXiv2022

High-order harmonic generation by sub-cycle laser pulses and associated scaling laws

We studied the high-harmonic generation by the interaction of sub-cycle laser pulses with the He atom. The sub-cycle pulses are modeled using the complex source vector beam model, which is an exact solution to Maxwell's equations and accurately models the sub-cycle field profiles. We observed that the harmonic cutoff could be extended with the variation of the sub-cycle pulse duration, mainly because of the inherent blueshift associated with shorter pulses. The scaling laws for the harmonic yield and harmonic cutoff energy with pulse duration and fundamental driver wavelengths are also deduced. Furthermore, a detailed wavelet analysis of harmonic generation by sub-cycle pulses is carried out. The appropriate filtering and superposition of the harmonics gave rise to a single attosecond pulse of duration ~ 100 as.

physics.optics↗

arXiv2021

Polarization control of attosecond pulses using bi-chromatic elliptically polarized laser

We study the higher-harmonic generation (HHG) using elliptically polarized two-color driving fields. The HHG via bi-chromatic counter-rotating laser fields is a promising source of circularly polarized ultrashort XUV radiation at the attosecond time scale. The ellipticity or the polarization of the attosecond pulses can be tweaked by modifying the emitted harmonics' ellipticity, which can be controlled by varying the driver fields. We propose a simple setup to control the polarization of the driving fields, which eventually changes the ellipticity of the attosecond pulses. A well-defined scaling law for the ellipticity of the attosecond pulse as a function of the rotation angle of the quarter-wave plate is also deduced by solving the time-dependent Schrodinger equation (TDSE) in two dimensions. The scaling law can further be explored to obtain the attosecond pulses of the desired degree of polarization, ranging from linear to elliptical to circular polarization.

physics.atom-ph↗

arXiv2021

Controlling resonant enhancement in higher-order harmonic generation

We present a method to tune the resonantly enhanced harmonic emission from engineered potentials, which would be experimentally feasible in the purview of the recent advances in atomic and condensed matter physics. The recombination of the electron from the potential dependent excited state to the ground state causes the emission of photons with a specific energy. The energy of the emitted photons can be controlled by appropriately tweaking the potential parameters. The resonant enhancement in high-harmonic generation enables the emission of very intense extreme ultra-violet or soft x-ray radiations. The scaling law of the resonant harmonic emission with the model parameter of the potential is also obtained by numerically solving the time-dependent Schrödinger equation in two dimensions.

physics.atom-ph↗

arXiv2020

Complete characterization of ultra-intense laser pulses in radiation damping regime

We report the first closed, analytical expression for the scattering angle of an electron bunch ponderomotively scattered from a counter-propagating, ultra-intense laser pulse, also accounting for radiation reaction (RR). The found formulation depends nontrivially on the laser intensity, pulse duration, beam waist, and energy of the electron bunch. For various laser and bunch parameters the proposed formula is in excellent quantitative agreement with full, relativistic test particle simulations in a realistic electromagnetic field configuration of a focused laser pulse. We also demonstrate how in the radiation dominated regime a simple rescaling of our model's input parameters yields excellent quantitative agreement with numerical simulations based on the Landau-Lifshitz model. Finally, we discuss how the model can be applied for an in-situ characterization of current and future ultra-high power laser systems, but also to experimentally probe fundamental properties of RR during ultra-intense laser electron interaction.

physics.plasm-ph↗

arXiv2020

Regulating the higher harmonic cutoffs via sinc pulse

We theoretically investigate the generation of higher harmonics and the construction of a single attosecond pulse by means of two oppositely polarized sinc-shaped driver pulses. In comparison to a few-cycle Gaussian pulse of the same energy, here we observe a significant broadening in the bandwidth of an XUV/soft-Xray supercontinuum spectrum in the synthesized pulse. Furthermore, we observe that the harmonic cutoff and its corresponding intensity follow a well-defined scaling with the {\it delay parameter} between the two pulses. In principle, this delay can easily be tuned in on an optical bench. The typical nature of the synthesized pulse ensures the generation of single attosecond pulse instead of a pulse train. In this case, we obtain a single attosecond pulse of duration $\sim 27$ as in XUV/soft-Xray regime of the electromagnetic spectrum. Depending on the delay parameter we observe an enhancement in some satellite harmonics. The proposed setup promises a highly tunable source of energetic photons, wherein the energy of the photons can easily be controlled from XUV to soft-Xray regime by simply changing the delay between two oppositely polarized sinc-pulses.

physics.atom-ph↗

arXiv2019

Ultra-intense laser pulse characterization using ponderomotive electron scattering

We present a new analytical solution for the equation of motion of relativistic electrons in the focus of a high-intensity laser pulse. We approximate the electron's transverse dynamics in the averaged field of a long laser pulse focused to a Gaussian transverse profile. The resultant ponderomotive scattering is found to feature an upper boundary of the electrons' scattering angles, depending on the laser parameters and the electrons' initial state of motion. In particular, we demonstrate the angles into which the electrons are scattered by the laser scale as a simple relation of their initial energy to the laser's amplitude. We find two regimes to be distinguished in which either the laser's focusing or peak power are the main drivers of ponderomotive scattering. Based on this result, we demonstrate how the intensity of a laser pulse can be determined from a ring-shaped pattern in the spatial distribution of a high-energy electron beam scattered from the laser. We confirm our analysis by means of detailed relativistic test particle simulations of the electrons' averaged ponderomotive dynamics in the full electromagnetic fields of the focused laser pulse.

physics.optics↗

arXiv2018

Dispersion of the laser pulse through propagation in underdense plasmas

The propagation of the laser pulses in the underdense plasma is a very crucial aspect of laser-plasma interaction process. In this work, we explored the two regimes of laser propagation in plasma, one with $a_0 < 1$ and other with $a_0 \gtrsim 10$. For $a_0<1$ case, we used a cold relativistic fluid model, wherein apart from immobile ions no further approximations are made. The effect of the laser pulse amplitude, pulse duration, and plasma density is studied using the fluid model and compared with the expected scaling laws and also with the PIC simulations. The agreement between the fluid model and the PIC simulations are found to be excellent. Furthermore, for $a_0 \gtrsim 10$ case, we used the PIC simulations alone. The delicate interplay between the conversion from the electromagnetic field energy to the longitudinal electrostatic fields results in the dispersion and so the red-shift of the pump laser pulse. We also studied the interaction of the dispersed pulse (after the propagation in underdense plasma) with the sub-wavelength two-layer composite target. The ions from the thin, low-density second layer are found to be efficiently accelerated to $\sim 70$ MeV, which is not found to be the case without dispersion.

physics.plasm-ph↗

arXiv2018

Chirp assisted ion acceleration via relativistic self induced transparency

We study the effect of the chirped laser pulse on the transmission and associated ion acceleration by the sub-wavelength target. In the chirped laser pulses, the pulse frequency has a temporal variation about its fundamental frequency, which manifests to the temporal dependence of the critical density ($n_c$). In this work we used a chirp model which is beyond the linear approximation. For negatively (positively) chirped pulses, the high (low) frequency component of the pulse interacts with the target initially followed by the low (high) frequency component. The threshold plasma density for the transmission of the pulse is found to be higher for the negatively chirped laser pulses as compared to the unchirped or positively chirped pulses. The enhanced transmission of the negatively chirped pulses for higher densities ($6n_c$) results in very efficient heating of the target electrons, creating a very stable and persistent longitudinal electrostatic field behind the target. The void of the electrons results in expansion of the target ions in either direction, resulting in the broad energy spectrum. We have introduced a very thin, low density ($< n_c$) secondary layer behind the primary layer. The ions from the secondary layer are then found to be accelerated as a mono-energetic bunch under the influence of the electrostatic field created by the primary layer upon interaction by the negatively chirped pulse. Under the optimum conditions, the maximum energy of the protons are found to be $\sim 100$ MeV for 10 fs (intensity fwhm); Circularly Polarized; Gaussian; negatively chirped laser pulse with peak intensity $\sim 8.5\times 10^{20}$ W/cm$^2$.

physics.plasm-ph↗

arXiv2017

Transition from wakefield generation to soliton formation

It is well known that when a short laser pulse propagates in an underdense plasma, it induces longitudinal plasma oscillations at the plasma frequency after the pulse, typically referred to as the 'wakefield'. However, for plasma densities approaching the critical density wakefield generation is suppressed, and instead the EM-pulse undergoes nonlinear self-modulation. In this article we have studied the transition from the wakefield generation to formation of quasi-solitons as the plasma density is increased. For this purpose we have applied a one dimensional (1D) relativistic cold fluid model, which has also been compared with particle-in-cell simulations. A key result is that the energy loss of the EM-pulse due to wakefield generation has its maximum for a plasma density of the order 10 percent of the critical density, but that wakefield generation is sharply suppressed when the density is increased further.

physics.plasm-ph↗