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Item Harmonic emission as a probe to coherent transitions in the topological superconductors(2025-07) Bandyopadhyay, Jayendra N.; Holkundkar, Amol R.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.Item Engineering harmonic emission through spatial modulation in a Kitaev chain(APS, 2025-09) Bandyopadhyay, Jayendra N.; Holkundkar, Amol R.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∈[−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≤0 regime, we observe the midgap 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.Item Control over the secondary collision of electron in high-order harmonic generation(IOP, 2024-06) Holkundkar, Amol R.We investigated the high-order harmonic generation by interacting linearly polarized laser pulses with the atomic target. The temporal evolution of harmonic emission and the underlying mechanisms of rescattering electrons are thoroughly investigated through a combination of quantum analysis and classical trajectory simulations. The manipulation of the carrier-envelope phase (CEP) provides a promising avenue for controlling electron recollisions, revealing a systematic linear relationship between ionization and recombination times across varying CEP values. Moreover, examining phase properties in emitted harmonics during secondary collisions presents intriguing modulations, offering a potential experimental approach to verify the presence of secondary recollisions.Item Probing topological phase transitions in the Aubry-Andre-Harper model via high-harmonic generation(APS, 2024-09) Holkundkar, Amol R.; Bandyopadhyay, Jayendra N.We study the high-harmonic generation (HHG) 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 a 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 yieldItem Role of interband and intraband current in laser interaction with bichromatic quasiperiodic crystals(APS, 2024-04) Bandyopadhyay, Jayendra N.; Holkundkar, Amol R.We study the role of the inter- and intraband current in the laser interaction with the bichromatic quasiperiodic 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 bichromatic potential ratios, the energy band structure of the “valence band” and the “conduction band” facilitates 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 is also studied for these bichromatic optical lattices, and the resultant harmonic yield is commented upon.Item Journal of Physics B: Atomic, Molecular and Optical Physics(IOP, 2020-09) Bandyopadhyay, Jayendra N.; Holkundkar, Amol R.We theoretically investigate the generation of higher harmonics and the construction of a single attosecond pulse (ASP) 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 the XUV/soft x-ray supercontinuum spectrum in the synthesized pulse. Furthermore, we observe that the harmonic cutoff and its corresponding intensity follow a well-defined scaling with the delay parameter between the two pulses. In principle, this delay can easily be tuned on an optical bench. The typical nature of the synthesized pulse ensures the generation of a single ASP instead of a pulse train. In this case, we obtain a single ASP with a duration of ∼27 attoseconds in the XUV/soft x-ray 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 the XUV to the soft x-ray regime by simply changing the delay between two oppositely polarized sinc-pulses.Item Strong-field ionization and fragmentation of large, gas-phase clusters in the few-cycle domain(ARXIV, 2010-05) Holkundkar, Amol R.Intense 3-cycle pulses (10 fs) of 800 nm laser light are utilized to measure energy distributions of ions emitted following Coulomb explosion of Arn clusters (n=400-900) upon their irradiation by peak intensitis of 5×1014 W cm−2. The 3-cycle pulses do not afford the cluster sufficient time to undergo Coulomb-driven expansion, resulting in overall dynamics that appear to be very different to those in the many-pulse regime. The peak ion energies are much lower than those obtained when 100 fs pulses of the same intensity are used; they are almost independent of the size of the cluster (over the range 400-900 atoms). Ion yields are a factor of 20 larger in the direction that is perpendicular to the laser polarization vector than along it. This unexpected anisotropy is qualitatively rationalized using molecular dynamics calculations in terms of shielding by an electronic charge cloud within the cluster that is spatially asymmetric.Item Magnetic mirror cavities as THz radiation sources and a means of quantifying radiation friction(ARXIV, 2014-06) Holkundkar, Amol R.We propose a radiation source based on a magnetic mirror cavity. Relativistic electrons are simulated entering the cavity and their trajectories and resulting emission spectra are calculated. The uniformity of the particle orbits is found to result in a frequency comb in terahertz range, the precise energies of which are tuneable by varying the electron's γ-factor. For very high energy particles radiation friction causes the spectral harmonics to broaden and we suggest this as a possible way to verify competing classical equations of motion.Item Ion acceleration 'via' relativistic self induced transparency in subwavelength target(ARXIV, 2016-07) Holkundkar, Amol R.In this work we have studied the effect of target thickness on relativistic self-induced transparency (RSIT) and found out that for subwavelength targets the corresponding threshold target density (beyond which target is opaque to incident laser pulse of a given intensity) increases. The accelerating longitudinal electrostatic field created by RSIT from subwavelength target is used to accelerate the ion bunch from a thin, low density layer behind the main target to ∼ 100 MeV. A suitable scaling law for optimum laser and target conditions is also deduced. The word `via' in the title signifies the fact that we are interested in acceleration of ions from the layer placed behind the target. It is also being observed that as per as energy spectrum is concerned; an extra low density layer is advantageous than relying on target ions alone.Item Effects of cluster size and spatial laser intensity distribution on fusion neutron generation by laser driven Deuterium clusters(ARXIV, 2016-02) Holkundkar, Amol R.three dimensional molecular dynamic code is used to study the generation of fusion neutrons from Coulomb explosion of Deuterium clusters driven by intense near infra-red (NIR) laser (λ=800nm) of femtosecond pulse duration (τ=50fs) under beam-target interaction scheme. We have considered various clusters of average sizes (⟨R0⟩=80,140,200Å) which are irradiated by a laser of peak spatial-temporal intensity of 1×1018W/cm2. The effects of cluster size and spatial laser intensity distribution on ion energies due to the Coulomb explosion of the cluster are included by convolution of single cluster single intensity ion energy distribution function (IEDF) over a range of cluster sizes and laser intensities. The final convoluted IEDF gets broadened on both lower and higher energy sides due to this procedure. Furthermore, the neutron yield which takes into account the convoluted IEDF, also gets modified by a factor of ∼2 compared to the case when convolution effects are ignored.