Laser Induced Processes

The Laser Induced Processes research group is active in research related to physico-chemical processes induced by coherent electromagnetic radiation in interaction with matter, from atoms and molecules to biological systems and nanostructures. By means of theoretical and experimental approaches we focus our efforts on the fundamental understanding of these processes as well as on developing new applications exploiting them.

Research topics:

  • Temporal / spectral characterization of ultrashort laser pulses using deep learning algorithms. Projects: ELI-RO
  • Propagation of femtosecond pulses and generation of attosecond pulses in laser-fabricated integrated photonic circuits. Projects: X-Pic
  • Ultrashort laser pulses’ interaction with atoms: modeling high-order harmonic generation in macroscopic conditions, attosecond pulse formation
  • Analysis of excited state dynamics induced by coherent electromagnetic radiation in molecular and supramolecular systems; Projects: PN-III-P4-ID-PCE-2020-0770
  • Fabrication of nanostructured films with controlled optical/plasmonic properties via colloidal self-assembly and colloidal lithography; Projects: PN-III-P4-ID-PCE-2020-1607
  • Direct laser-writing lithography, from nano to millimetric scale structures
  • Development of molecular optical sensors exploiting the plasmonic enhancement of analyte-laser light interactions (SERS, SEF). Projects: RO-NO-2019-0517, PN-III-P2-2.1-PED-2019-5473
  • Photoinduced ultrafast phenomena in hybrid metal-semiconductor nanomaterials investigated by time-resolved spectroscopy. Projects: PN-III-P1-1.1-TE-2019-1141
  • Characterizations through optical coherence tomography techniques and development of contrast agents
  • Determination of thermal parameters of porous solids through photopyroelectric calorimetry: methodology development and optimization of experimental conditions.

Team Leader

Dr. Cosmin FARCĂU – Scientific Researcher I
Expertise: Colloidal self-assembly, fabrication of periodically nanostructured films, Raman/SERS and fluorescence spectroscopy, plasmonic properties (experiment and FDTD simulations).


Dr. Attila BENDE – Scientific Researcher I
Expertise: Atomic, Molecular and Chemical Physics; Theoretical Chemistry; Physical Chemistry.

PhD student Maricel BOCĂNEALĂResearch Assistant
Expertise: Bioinformatics, Microbiology.

Dr. Radu BRĂTFĂLEAN – Scientific Researcher II

Phd student Denisa-Corina CUIBUSResearch Assistant
Expertise: Nanoparticles and microparticles, UV-VIS.

Dr. Dorin Nicolae DĂDÂRLATScientific Researcher I
Expertise: Solid State Physics, Optics.

Dr. Alexandra FĂLĂMAȘ – Scientific Researcher II
Expertise: Optical, Atomic, and Molecular Physics; Vibrational spectroscopy; Time-resolved absorption and fluorescence spectroscopy; Nanotechnology.

Phd student Alex-Adrian FARCAȘScientific Researcher
Expertise: Atomic, Molecular and Chemical Physics, Theoretical Chemistry, Physical Chemistry.

Dr. Ana Maria Mihaela GHERMANScientific Researcher
Expertise: .

Dr. Katalin KOVÁCS – Scientific Researcher I
Expertise: Nonlinear Optics, Laser – matter interaction, Attosecond Physics.

Ioana MARICAResearch Assistant
Expertise: Vibrational spectroscopy (Raman), Atomic, molecular and optical physics, Absorption and fluorescence spectroscopy.

Dr. Cristina MUNTEAN – Scientific Researcher I
Expertise: Vibrational spectroscopy of nucleic acids.

Dr. Florin TOADERE – Scientific Researcher III
Expertise: Image processing, Medical optical imaging, VIS spectroscopy.

Dr. Nicoleta TOȘA – Scientific Researcher II
Expertise: Organic, Inorganic and Analytical Chemistry; Physical Chemistry; Spectroscopy; Material Science and Engineering.

Dr. Valer TOȘA – Scientific Researcher I
Expertise: High order harmonics and attosecond pulse generation, Femtosecond pulse propagation in ionizing gases and guided structures, Modeling migration in polymeric multilayer structures.

Dr. István Ferenc TÓTHScientific Researcher
Expertise: .

Dr. Carmen TRIPON – Scientific Researcher II
Expertise: Atomic, Molecular and Chemical Physics.

Photoionization, Structures, and Energetics of Na-Doped Formic Acid–Water Clusters, Journal Cover

Attila Bende, Maria F. Gaele and Tonia M. Di Palma

Abstract: The influence of formic acid on water cluster aggregation hasbeen investigated experimentally by mass spectrometry andtunable UV laser ionization applied to Na-doped clusters formedin the supersonic expansion of water vapors seeded with formicacid (FA) as well as theoretically using high level quantumchemistry methods. The mass spectra of Na-FA(H2O)n clustersshow an enlarging of mass distribution toward heavier clusterswith respect to the Na-(H2O)n clusters, suggesting similar massdistribution in neutral clusters and an influence of formic acid inwater aggregation. Density functional theory and coupled-clustertype (DLPNO-CCSD(T)) calculations have been used tocalculate structures and energetics of neutral and ionizedNa-FA(H2O)n as well as neutral FA(H2O)n. Na-doped clusters arecharacterized by very stable geometries. The theoreticaladiabatic ionization potential values match pretty well themeasured appearance energies and the calculated first sixelectronic excited states show Rydberg-type characters, indicatingpossible autoionization contributions in the mass spectra.Finally, theoretical calculations on neutral FA(H2O)n clustersshow the possibility of similarly stable structures in smallclusters containing up to n=4–5 water molecules, where FAinteracts significantly with waters. This suggests that FA cancompete with water molecules in the starting stage of theaggregation process, by forming stable nucleation seed.

Journal: ChemPhysChem, Vol. 23, Iss. 5 Art. Nr. e202100861 (2022)

Compact intense extreme-ultraviolet source

B. Major, O. Ghafur, K. Kovács, K. Varju, V. Toșa, M. J. J. Vrakking, B. Schutte

Abstract: High-intensity laser pulses covering the ultraviolet to terahertz spectral regions are nowadays routinely generated in a large number of laboratories. In contrast, intense extreme-ultraviolet (XUV) pulses have only been demonstrated using a small number of sources including free-electron laser facilities and long high-harmonic generation (HHG) beamlines. Here, we demonstrate a concept for a compact intense XUV source based on HHG that is focused to an intensity of 2 x 1014 W/cm2, with a potential increase up to 1017 W/cm2 in the future. Our approach uses tight focusing of the near-infrared (NIR) driving laser and minimizes the XUV virtual source size by generating harmonics several Rayleigh lengths away from the NIR focus. Accordingly, the XUV pulses can be refocused to a small beam waist radius of 600 nm, enabling the absorption of up to four XUV photons by a single Ar atom in a setup that fits on a modest (2 m) laser table. Our concept represents a straightforward approach for the generation of intense XUV pulses in many laboratories, providing exciting opportunities for XUV strong-field and nonlinear optics experiments, for XUV-pump XUV-probe spectroscopy and for the coherent diffractive imaging of nanoscale structures.

Journal: Optica, Vol. 8, Issue 7, pp. 960-965 (2021)

Generation of two successive attosecond pulses in separate spectral domains

K. Kovács and V. Toșa
Abstract: We demonstrate that two different single attosecond pulses (SAP) can be obtained from naturally separated spectral domains formed during high-order harmonic generation and propagation in a gas medium. We propose a feasible experimental configuration in which one can obtain an SAP in a lower energy domain (<300 eV), or another SAP in a higher energy domain (>300 eV). Without filtering, a double attosecond pulse emission with fixed temporal separation is obtained. The gap between the two spectral domains is close to the onset of the water window.

Journal: Scientific Reportsy, Vol. 10, pp. 7392 (2020)

Tunable plasmonic response of metal-coated microsphere arrays

N. Nechita and C. Farcău

Abstract: The overall optical response (transmittance, reflectance, and absorbance) of metal film over nanospheres (MFoN) is studied for a wide range of sphere diameters (200 – 1000 nm) and metal film thicknesses (40-200 nm), over the 450 – 2000 nm spectral range. Analyses are performed also in water, with microfluidic surface-enhanced Raman scattering applications in mind. Two main outcomes are the dependence of the plasmonic absorbance band on structural parameters and the behavior in aqueous environment. The parameter ranges for targeting common lasers (633 and 785 nm) are identified. Additionally, for larger sphere size and thicker films, a new absorbance band was identified, exhibiting a multipole-like electric field distribution, different than the dipole-like fields at the main absorption band. It is also shown that the fine morphology of the metal film at the inter-sphere region has a strong impact on reflectance (and absorbance) but not transmittance. The individual roles of the metal particles formed on the substrate or the dielectric sphere array on the overall optical response are discussed. Finally, the role of the metal type (Au, Ag, Cu, Al) is also analyzed.

Journal: Optic Express, Vol. 29, pp. 42238-42250 (2021)

Plasmonic photothermal heating of gold nanostars

A. M. M. Gherman, S. Boca, A. Vulpoi, M. V. Cristea, C. Farcău and V. ToșaAbstract: The ability of noble metal nanoparticles (NPs) to convert light into heat has triggered a lot of scientific interest due to the numerous potential applications, including, e.g. photothermal therapy or laser-based nanopatterning. In order for such applications to be practically implemented, the heating behaviour of NPs embedded in their surrounding medium has to be thoroughly understood, and theoretical models capable of predicting this behaviour must be developed. Here we propose a multiscale approach for modelling the photothermal response of a large ensemble of nanoparticles contained within a cm-scale, real-size container. Electromagnetic field, ray tracing and heat transfer simulations are combined in order to model the response of nanostars and nanospheres suspensions contained within a common Eppendorf tube. To validate the model, gold nanostars are then synthesised and characterized by electron microscopy and optical spectroscopy. Laser-induced heating experiments are conducted by irradiating colloid-filled Eppendorf tubes with a 785 nm continuous wave laser and monitoring by a thermographic camera. The experimental results confirm that the proposed model has potential for predicting and analysing the heating efficiency and temperature dynamics upon laser irradiation of plasmonic nanoparticle suspensions in real-scale containers, at cm3 volumes.

Journal: Nanotechnology, Vol. 31, pp. 125701 (2020)

Propagation-enhanced generation of intense high-harmonic continua in the 100-eV spectral region

D. E. Rivas, B. Major, M. Weidman, W. Helml, G. Marcus, R. Kienberger, D. Charalambidis, P. Tzallas, E. Balogh, K. Kovács, V. Toșa, B. Bergues, K. Varjú, and L. Veisz

Abstract: The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids.

Journal: Optica Vol. 5, Issue 10, pp. 1283-1289 (2018)

Light-induced spin transitions in Ni(II)-based macrocyclic-ligand complexes: A DFT study

Attila Bende, Maria F. Gaele, Tonia M. Di PalmaAbstract: Light-induced intersystem crossings in different Ni(II) macrocyclic ligand complexes with square-pyramidal and octahedral ligand-metal coordination have been investigated by means of static (DFT) and time-dependent density functional theory (TD-DFT) calculations, considering the MN12-SX exchange-correlation (XC) functional together with the def2-TZVP basis set. For the quantitative validation of the applied XC functional, the theoretical UV absorption spectra of azopyridine functionalized Ni-porphyrin macrocyclic ligand complex with square-pyramidal coordination have been compared with the experimental results obtained by Venkataramani et al. (Science, 331 (2011) 445). Using the TD-DFT method, the stability of the light–mediated reversible ligand coordination and the switching of magnetic properties have been characterized by identifying the active electronic excited states both in singlet and triplet spin configuration involved in the light-induced excited spin-state trapping. The location of the intersystem crossing points between different spin states has been performed and the strength of the spin-orbit coupling between them has been computed.

Journal: Journal of Photochemistry and Photobiology A: Chemistry Vol. 376, pp. 316-323 (2019)

Artificial Neural Network Trained to Predict High-Harmonic Flux

Ana Maria Mihaela Gherman, Katalin Kovács, Mircea Vasile Cristea and Valer ToșaAbstract: In this work we present the results obtained with an artificial neural network (ANN) which we trained to predict the expected output of high-order harmonic generation (HHG) process, while exploring a multi-dimensional parameter space. We argue on the utility and efficiency of the ANN model and demonstrate its ability to predict the outcome of HHG simulations. In this case study we present the results for a loose focusing HHG beamline, where the changing parameters are: the laser pulse energy, gas pressure, gas cell position relative to focus and medium length. The physical quantity which we predict here using ANN is directly related to the total harmonic yield in a specified spectral domain (20–40 eV). We discuss the versatility and adaptability of the presented method.

Journal: Applied Sciences Vol. 8, Issue 11, Art. Nr. 2106 (2018)

Macroscopic attosecond chirp compensation

Katalin Kovács and Valer Toșa

Abstract: We numerically study the physical mechanism of the chirp compensation of the attosecond XUV pulses obtained by high-order harmonic generation. We show by detailed analysis that the macroscopic aspects of fundamental pulse propagation are essential in the formation and temporal-spectral-spatial properties of the attosecond pulses. Partial chirp compensation is already achievable due to the self-phase-modulation of the fundamental pulse. Further, by propagating the attosecond pulses in preformed plasma, we can fully compensate the inherent positive chirp of the attosecond pulses which were built up from the short electron trajectories in the harmonic generation process.

Journal: Optics Express Vol. 27, Issue 15, Art. Nr. 21873 (2019)

Metal-coated microsphere monolayers as surface plasmon resonance sensors operating in both transmission and reflection modes

Cosmin Farcău

Abstract: Metal-coated microsphere monolayers (MCM) are a class of plasmonic crystals consisting of noble metal films over arrays of self-assembled colloidal microspheres. Despite their ease of fabrication and tunable plasmonic response, their optical sensing potential has been scarcely explored. Here, silver coated polystyrene sphere monolayers are proposed as surface plasmon resonance sensors capable of functioning in both transmission (T) and reflection (R) readout modes. An original and key point is the use of ~200 nm colloids, smaller than in MCM studied before. It allowed us to reveal a previously unobserved, additional/secondary Enhanced Optical Transmission band, which can be exploited in sensing, with higher sensitivity than the better-known main transmission band. The reflection configuration however, is almost an order of magnitude more efficient for sensing than the transmission one. We also evidenced a strong impact of the adsorbate location on the metal surface on the sensing efficiency. Electric field distribution analysis is performed to explain these results. Proof-of-concept experiments on the detection of 11-MUA molecular monolayers, performed in both readout modes, confirm the behaviors observed through FDTD simulations. Results in this paper can serve as guidelines for designing optimized sensors based on metal-coated colloidal monolayers, and more generally for plasmonic sensors based on metal nanostructured films.

Journal: Scientific Reports Vol. 9, Art. Nr. 3683 (2019)

Graphene/silver nanoparticles‐based surface-enhanced Raman spectroscopy detection platforms: Application in the study of DNA molecules at low pH

Cristina M. Muntean, Nicoleta E. Dina, Maria Coroş, Nicoleta Toşa, Alexandru I. Turza and Monica DanAbstract: The aim of this work is to develop a SERS-active platform based on a mixture of graphene/Ag nanocomposite and a silver colloid for biomedical applications and to test it in the case of DNA molecules at low pH. Graphene/silver nanocomposites were synthesized by the reduction process and were characterized by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) patterns and thermogravimetric analysis (TGA). The following graphene/Ag composites were prepared: a) TRGO („Thermally Reduced Graphene Oxide”), containing about 2-3% silver nanoparticles (AgNPs); b) TRGO 1 (graphene with crowded AgNPs 20%) and c) TRGO 2 (graphene with ordered AgNPs 20%). Different mixtures of these systems with a silver colloid were tested by UV-Vis spectrophotometry and also by surface-enhanced Raman spectroscopy (SERS) in the presence of the test substance crystal violet. Moreover, the time stability of the mixtures of graphene/AgNPs composite (TRGO 1) with the silver colloid was tested for crystal violet. Based on these results, the platform with the best SERS enhancement properties was selected for DNA analyses at low pH values. Chemical stability under acidic conditions has been found for nucleic acid systems, in the presence of graphene/crowded AgNPs 20% and silver colloid. This chemical stability has been discussed considering a hydracid catalyzed electrophilic hydration reaction mechanism characteristic to the trans-1,3-butadiene type building moieties from graphene.

Journal: Journal of Raman Spectroscopy Vol. 50, Issue 12, pp. 1849-1860 (2019)

Vibrational relaxation of the backbone and base modes in LacDNA complexes by UV resonance Raman spectroscopy

Cristina M. Muntean, Ioan Bratu and Antonio Hernanz

Abstract: Vibrational band shape analysis through time correlation function concept is widely used to obtain experimental information on the molecular dynamics of medium size molecules in different environments. Interesting details are revealed by extending this technique to biomolecules such as functional groups of the nucleic acids in media approaching the physiological conditions. In this work a study into the UV resonance Raman (UVRR) vibrational half bandwidths of functional groups in LacDNA, upon lowering the pH (pH 6.4, pH 3.45) and in the presence of Mn2+ and Ca2+ ions, respectively, was of interest. The corresponding global relaxation times have been derived. Also, the 793 cm-1 UVRR band, corresponding to ν (backbone O-P-O, dT) oscillator of LacDNA in aqueous solutions was selected for band shape analysis. Vibrational relaxation appears as the dominant relaxation process for this mode, vibrational dephasing being the most efficient for this oscillator. Current theories developed for vibrational dephasing have been applied to this profile and relevant relaxation parameters have been obtained and discussed. To our knowledge this is the first study on DNA oligomers vibrational band shape analysis through time correlation function concept.

Journal: The Journal of Physical Chemistry B Vol. 121, Issue 28, pp. 6909-6918 (2017)

  • “Federico II” University, Department of Physical Sciences, Naples, Italy
    Modelling the propagation of ultrashort laser pulses in gases and atmosphere
  • Ultrashort Quantum Beam Facility, GIST ( Gwangju Institute of Science & Technology), Korea
    Harmonic generation by chirped and self-guided laser pulses
  • ELI-ALPS Research Institute, Szeged, Hungary and Max Born Institut Berlin, Germany
    Optimizing attosecond pulse generation
  • Fabes Research GmbH, Munich, Germany
    Modelling substance diffusion in multilayer polymer systems
  • Debrecen University, Theoretical Physics Department, Debrecen, Hungary
    Ultrafast physical processes in atoms, molecules, nanostructures and biological systems
  • SINTEF AS, Oslo, Norway
  • “Iuliu Hațieganu” University of Medicine and Pharmacy, Analytical Chemistry Dept., Oslo, Norway
  • NanomMems SRL, Rasnov, Romania
    Development of Electrochemical-Surface Enhanced Raman Spectroscopy mcrofluidic-integrated molecular sensors