The Laser Induced Processes research group develops theoretical and experimental research related to physico-chemical processes induced by coherent electromagnetic radiation in interaction with atomic, molecular and biological systems.
Theoretical research aims
- modeling the propagation of ultra-short (femtosecond) laser pulses in ionizing gas environments,
- modeling the generation of pulses with attosecond pulse duration (10-18 s),
- the study of the relaxation processes of the excited electronic states induced by the coherent electromagnetic radiation.
Experimental research has as main targets
- the study of the dynamics of absorption and emission processes, respectively by time-resolved spectroscopy,
- investigation of specific phenomena induced by radiation in atomic, molecular and biological systems,
- characterizing the response of nano-objects induced by the laser radiation,
- nonlinear phenomena in complex systems at the nanometric scale.
Dr. Valer TOȘA – Scientific Researcher I
Expertise: Atomic and Molecular Physics, Numerical Modeling, Nonlinear Optics.
Dr. Attila BENDE – Scientific Researcher I
Expertise: Atomic, Molecular and Chemical Physics; Theoretical Chemistry; Physical Chemistry.
PhD student Maricel BOCĂNEALĂ – Research Assistant
Expertise: Bioinformatics, Microbiology.
Dr. Radu BRĂTFĂLEAN – Scientific Researcher II
Dr. Dorin Nicolae DĂDÂRLAT – Scientific 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 FARCAȘ – Scientific Researcher
Expertise: Atomic, Molecular and Chemical Physics, Theoretical Chemistry, Physical Chemistry.
Dr. Cosmin FARCĂU – Scientific Researcher I
Expertise: Physics, Optical spectroscopy, Nanotechnology.
Dr. Ana Maria Mihaela GHERMAN – Scientific Researcher
Dr. Katalin KOVÁCS – Scientific Researcher I
Expertise: Nonlinear Optics, Laser – matter interaction, Attosecond Physics.
Ioana MARICA – Research Assistant
Dr. Cristina MUNTEAN – Scientific Researcher I
Expertise: Vibrational spectroscopy of nucleic acids.
Narcisa Laura NECHITA – Scientific Researcher
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. István Ferenc TÓTH – Scientific Researcher
Dr. Carmen TRIPON – Scientific Researcher II
Expertise: Atomic, Molecular and Chemical Physics.
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.
Metal-coated microsphere monolayers as surface plasmon resonance sensors operating in both transmission and reflection modes
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
- Korean Advanced Institute of Science and Technology, Daejeon, Korea
Harmonic generation by chirped and self-guided laser pulses
- ELI-ALPS Research Institute, Szeged, Hungary
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
- “Federico II” University, Department of Physical Sciences, Naples, Italy