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Bhaskar De

Publications and source records attributed to Bhaskar De.

12 recordsLinked to original sources
arXiv2026

Pulse-Burst Excitation Reveals Time-Dose Reciprocity Breakdown in Mixed-Halide Perovskites

Time-dose reciprocity, commonly associated with the Bunsen-Roscoe law, states that the response of a photosensitive system depends only on the total exposure dose, regardless of how that energy is delivered over time. Light-sensitive processes in mixed-halide perovskites, such as photoinduced halide segregation, often exhibit threshold-like behavior that may violate this principle and enable material-state control by photon timing. We test this using pulse-burst excitation, which introduces an additional temporal control dimension beyond conventional parameters such as pulse fluence, repetition rate, and average power. By redistributing the same photon dose over microsecond-to-millisecond timescales, we create distinct nonequilibrium excitation conditions and show that mixed-halide perovskites can evolve into different metastable states, revealing a breakdown of time-dose reciprocity in the combined processes of halide segregation and remixing. This additional temporal degree of freedom not only enables control of the material state but also provides a new experimental framework for disentangling the competing processes underlying photoinduced halide redistribution. Our findings establish photon timing as a control parameter for perovskite photochemistry and open additional opportunities for optical memory and neuromorphic photonic applications.

cond-mat.mtrl-sci↗
arXiv2025

Quantitative Lineshape Analysis for Arbitrary Inhomogeneity in Two-Dimensional Coherent Spectroscopy

Two-dimensional coherent spectroscopy (2DCS) provides simultaneous measurement of homogeneous and inhomogeneous linewidths through quantitative lineshape analysis. However, conventional lineshape analysis methods assume Gaussian inhomogeneity, limiting its applicability to systems with non-Gaussian inhomogeneity. We present a quantitative lineshape analysis method incorporating arbitrary inhomogeneity using a bivariate spectral distribution function in 2DCS simulations. An algorithm is developed to extract the homogeneous linewidth and arbitrary inhomogeneous distribution from experimentally-measured 2D spectrum. We demonstrate this framework for a quantum-well-exciton resonance with non-Gaussian inhomogeneity. This work broadens the scope of quantitative lineshape analysis for studying materials with non-Gaussian inhomogeneity.

physics.optics↗
arXiv2024

Coherent Nonlinear Optical Response for High-Intensity Excitation

Calculation of the coherent nonlinear response of a system is essential to correctly interpret results from advanced techniques such as two-dimensional coherent spectroscopy (2DCS). Usually, even for the simplest systems, such calculations are either performed for low-intensity excitations where perturbative methods are valid and/or by assuming a simplified pulse envelope, such as a $\delta$-function in time. Here, we use the phase-cycling method for exact calculation of the nonlinear response without making the aforementioned approximations even for high-intensity excitation. We compare the simulation results to several experimental observations to prove the validity of these calculations. The saturation of the photon-echo signal from excitons in a semiconductor quantum well sample is measured. The excitation-intensity dependent measurement shows nonlinear contributions up to twelfth order. Intensity-dependent simulations reproduce this effect without explicitly considering higher-order interactions. Additionally, we present simulation results that replicate previously-reported experiments with high-intensity excitation of semiconductor quantum dots. By accurately reproducing a variety of phenomena such as higher-order contributions, switching of coherent signal, and changes in photon-echo transients, we prove the efficacy of the phase-cycling method to calculate the coherent nonlinear signal for high-intensity excitation. This method would be particularly useful for systems with multiple, well-separated peaks and/or large inhomogeneity.

physics.optics↗
arXiv2023

Exciton-exciton Interactions -- A Quantitative Comparison Between Complimentary Phenomenological Models

Many-body interactions (MBIs) such as exciton-exciton interactions significantly affect the optical response of semiconductor nanostructures. These interactions can be rigorously modeled through microscopic calculations. However, these calculations can be computationally intensive and often lack physical insights. An alternative is to use phenomenological many-body interaction models such as the modified optical Bloch equations (MOBEs) and the anharmonic oscillator (AO) model. While both these models have separately been used to interpret experimental data, to the best of our knowledge, an explicit and direct correspondence between these models has not been established. Here, we show the empirical equivalence between these two complimentary MBI models through two-dimensional coherent spectroscopy simulations. A quantitative correspondence between the MBI parameters used in the two models are obtained. We also perform a quantitative comparison of these MBI models with experiments, which highlights the usefulness of these phenomenological models in interpreting experimental results.

cond-mat.mes-hall↗
arXiv2014

Non-extensive Statistics and Understanding Particle Production and Kinetic Freeze-out Process from $p_T$-spectra at 2.76 TeV

An approach, based on Tsallis non-extensive statistics, has been employed, here, to analyse, systematically, the $p_T$-spectra of various identified secondary hadrons like pions, kaons, protons and antiprotons, produced in different central $Pb+Pb$ interactions at LHC energy 2.76 TeV in terms of multiplicity and temperature fluctuations. The results, thus obtained, have been utilized to understand the various stages of different types of hadron production during evolution of the fireball produced in such collisions.

nucl-th↗
arXiv2014

Non-extensive Statistics and a Systematic Study of Meson-Spectra at LHC Energy $\sqrt{s_{NN}}=2.76$ TeV

The transverse momentum spectra of secondary pions and kaons, produced in $P+P$ and various central $Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV at LHC, have been analyzed systematically with an approach based on Tsallis non-extensive statistics. The analytical results have been utilized to determine some of the very important thermodynamical parameters bearing characteristic signatures of the partonic medium produced in such collisions.

nucl-th↗
arXiv2004

Rapidity Spectra of the Secondaries Produced in Heavy Ion Collisions and the Constituent Picture of the Particles

The present study is both a reanalysis and an extension of the approach initiated by Eremin and Voloshin(referenced in the text). We attempt to interpret here the rapidity-spectra of the various particles produced in both $Pb+Pb$ and $Au+Au$ collisions at CERN-SPS and RHIC-BNL. The study made here is wider in scope and is more species-specific than the earlier ones for which the results obtained here have been compared with those suggested by some previous works based on HIJING, VENUS etc, at various centralities. The study reconfirms that the constituent parton picture of the particles provides a better and more unified description of the rapidity-density yields for the various secondaries, including some light cluster particles like deuteron even in heavy ion collisions.

nucl-th↗
arXiv2003

Centrality-dependence of Particle Production at RHIC and the Combinational Approach

The newly proposed combinational approach, called the grand combinational model (GCM), as would be described in detail in the text, is still under our careful scrutiny. By applying it, we have attempted to analyze here the characteristics of both the transverse momentum($p_{\rm{T}}$)-, and centrality-dependence of production of the main varieties of the secondaries measured in $AuAu$ collisions at BNL-RHIC at both $\sqrt{s_{\rm{NN}}}=130$ GeV and $\sqrt{s_{\rm{NN}}}=200$ GeV by PHENIX Collaboration. Besides, with the help of it, we have also investigated the nature of centrality-dependence of the average transverse momenta of the various major categories of particles in $AuAu$ collisions at RHIC. The model seems to survive quite smoothly the acid tests of the latest PHENIX data, as it accommodates data modestly well on these twin aspects. The study reveals a kind of universality of nature of the hadronic secondaries and also of the basic particle and nuclear interactions at high energies. However, in the end, we precisely point out both the strengths and limitations of the specific model under consideration here.

hep-ph↗
arXiv2003

The $p_T$-Spectra of Some Non-pion Secondaries in High Energy NN to NA/AA Collisions and the Combinational Approach

In continuation of our perusal of the studies on transverse momentum spectra for the main varieties of secondaries from a consistent and comprehensive phenomenological approach, we propose to take up here -- after a successful completion of reporting in detail the results (Ref.[4] in the text) on our analyses of the $p_T$-spectra of pions -- the studies specially on production of kaons, protons and antiprotons in several proton-induced and nucleus-involved collisions at high energies. The measured data on inclusive cross sections of kaons, protons and antiprotons from the various published sources have here been assorted first. Next, data on the $p_T$-spectra of the specific secondaries produced in PP and $P\bar{P}$ reactions have been scanned and analyzed with the help of Hagedorn's model(HM). Thereafter a connector, named here the combinational approach(CA), has been constructed and used to analyze the data on $p_T$-spectra of some major category of non-pion secondaries produced in nucleus-nucleus(AA/AB) collisions at high energies. And these exercises have, finally, led to the modestly successful interpretations of a wide band of data with the revelation of some insightful physical aspects of high energy interactions. The limitations of the approach have also been precisely pointed out in the end.

hep-ph↗
arXiv2003

Transverse Mass Distribution Characteristics of $π^0$ Production in $^{208}$Pb-induced Reactions and the Combinational Approach

The nature of invariant cross-sections and multiplicities in some $^{208}Pb$-induced reactions and some important ratio-behaviours of the invariant multiplicities for various centralities of the collision will here be dealt with in the light of a combinational approach which has been built up in the recent past by the present authors. Next, the results would be compared with the outcome of some of the simulation-based standard models for multiple production in nuclear collisions at high energies. Finally, the implications of all this would be discussed.

nucl-th↗
arXiv2002

Transverse Momentum Spectra of Pions in Particle and Nuclear Collisions and Some Ratio-Behaviours: Towards A Combinational Approach

The nature of transverse momentum dependence of the inclusive cross-sections for secondary pions produced in high energy hadronic($PP$), hadronuclear($PA$) and nuclear($AA$) collisions has here been exhaustively investigated for a varied range of interactions in a unified way with the help of a master formula. This formula evolved from a new combination of the basic Hagedorn's model for particle(pion) production in PP scattering at ISR range of energies, a phenomenological approach proposed by Peitzmann for converting the results of $NN(PP)$ reactions to those for either $PA$ or $AA$ collisions, and a specific form of parametrization for mass number-dependence of the nuclear cross sections. This grand combination of models(GCM) is then applied to analyse the assorted extensive data on various high energy collisions. The nature of qualitative agreement between measurements and calculations on both the inclusive cross-sections for production of pions, and some ratios of them as well, is quite satisfactory. The modest successes that we achieve here in dealing with the massive data-sets are somewhat encouraging in view of the diversity of the reactions and the very wide range of interaction energies.

nucl-th↗