Vasilis Menelaos Dimitriou

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• Professor
• Professor at Hellenic Mediterranean University

In this paper, we present a novel scheme for the controlled generation of tunable narrowband γ -ray radiation by ultrarelativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which the excitation of a silicon single crystal along the (100) planar direction by a piezoe...

The integration of Finite Element Method (FEM) simulations with laser-based techniques has significantly advanced acoustic research by enhancing wave measurement, analysis, and prediction in complex solid media. This review examines the role of the FEM in laser-based acoustics for wave propagation, defect detection, biomedical diagnostics, and engi...

Acoustic metamaterials and phononic crystals are progressively consolidating as an important technology that is expected to significantly impact the science and industry of acoustics in the coming years. In this work, the impact of unit cell multiplicity on the spectral features of the acoustic response of phononic crystals is systematically studie...

The complex frequency domain assurance criterion is here applied for the comparison of a pristine to an altered state of a vibrating system. The criterion was originally proposed for the detection of defects in vibrating structures, while in later research studies it has been successfully used in musical acoustics. In this paper, we evaluate the di...

Using different laser irradiation patterns to modify the silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scannin...

This work describes an integrated method for the investigation of the vibrational characteristics of 3D printed tzouras top plates. The top plates vary in thickness, in tandem to the dimensions of a wooden instrument. The frequency response of the manufactured top plates is determined by modal measurements and the vibration modes are visualized usi...

We investigate the CW fiber laser - aluminum 1050 alloy interactions. The manufacturing processes of laser marking, engraving, and cutting are studied by experiments and numerical simulations. The laser head Precitec LightCutter 2.0 motorized 3D is mounted on a 3-Axis CNC milling machine, assembled with the Pipa-Q connector and the powerful CW 2kW...

Using different laser irradiation patterns to modify of silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scanning...

This work presents the current research activities within the framework of the European project TECHNO-CLS, aimed at developing novel narrow-band γ-ray sources via positron undulation by acoustically driven crystalline undulators. The controlled generation of γ-radiation with narrow bandwidth is crucial in modern scientific and technological applic...

Phononic Crystals and Acoustic Metamaterials are an emerging key-enabling technology that is expected to play a significant role in the science and industry of acoustics in the coming years. Until now, the evaluation of acoustic meta-structures has been carried out using traditional methods such as impedance tubes and electromagnetic loudspeakers....

The irradiation of solid materials by pulsed lasers is essential in studying their structure and properties. The purpose of this research is the computational study, through simulations, of the thermal and mainly acoustic behaviour of solid silicon (Si) targets under irradiation by short laser pulses of varying intensity. The simulation results sho...

In recent years, the use of ultra-high-frequency acoustic waves for the dynamic and controlled modulation of crystalline solids has found significant applications in material science, industry and in optoacoustic technology. The generation of these acoustic waves in crystals is achieved by various methods, such as piezoelectric transducers and exci...

In this paper we present a novel scheme for the controlled generation of of tunable narrowband gamma-ray radiation by ultra-relativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which excitation of a silicon single crystal along the (100) planar direction by a piez...

An integrated method of determining the vibration characteristics of musical instruments is here presented. The method includes modal measurements and holographic imaging, FEM modelling and simulations. Parts of musical instruments made of composite materials have been simulated, printed and measured. The vibrational response of 3D printed cymbals...

Phononic crystals and acoustic metamaterials are expected to become an important enabling technology for science and industry. Currently, various experimental methods are used for evaluation of acoustic meta-structures, such as impedance tubes and anechoic chambers. Here we present a method for the precise characterization of acoustic meta-structur...

A novel 3D auto-drum machine system for the generation and recording of percussion sounds is developed and presented. The capabilities of the machine, along with a calibration, sound production, and collection protocol are demonstrated. The sounds are generated by a drumstick at pre-defined positions and by known impact forces from the programmable...

The Department of Music Technology and Acoustics of the Hellenic Mediterranean University offers a unique higher education program in Greece, addressing the growing demand for specialists in music technology, sound technology, and acoustics. It aims to educate specialized professionals in the rapidly advancing scientific fields of music technology...

The evolution of musical instrument manufacturing has prompted a quest for innovative materials beyond traditional wood. This review explores the utilization of composite materials, 3D-printed materials, and metamaterials as favorable alternatives. The investigation is driven by challenges such as the scarcity of high-quality tonewoods, variations...

We introduce a novel, gaseous target optical shaping laser set-up, capable to generate short scale length, near-critical target profiles via generated colliding blast waves. These profiles are capable to maintain their compressed density for several nanoseconds, being therefore ideal for laser-plasma particle acceleration experiments in the near cr...

The present study encompasses a thorough analysis of the vibrations in a splash musical cymbal. The analysis is performed using a hybrid methodology that combines experimental measurements with parametric computer-aided design and finite element method simulations. Experimental measurements, including electronic speckle pattern interferometry, and...

Laser plasma-based accelerators provide an excellent source of collimated, bright, and adequately coherent betatron-type x-ray pulses with potential applications in science and industry. So far the laser plasma-based betatron radiation has been described within the concept of classical Liénard–Wiechert potentials incorporated in particle-in-cell si...

The dynamic behavior of solid Si targets irradiated by nanosecond laser pulses is computationally studied with transient, thermοmechanical three-dimensional finite element method simulations. The dynamic phase changes of the target and the generation and propagation of surface acoustic waves around the laser focal spot are provided by a finite elem...

Laser WakeField Acceleration (LWFA) is extensively used as a high-energy electron source, with electrons achieving energies up to the GeV level. The produced electron beam characteristics depend strongly on the gas density profile. When the gaseous target is a gas jet, the gas density profile is affected by parameters, such as the nozzle geometry,...

The plasma focus machine is a powerful tool for studying plasma dynamics and harnessing its potential in various applications like medicine and industry. In this paper, we present an upgrade version of the Mather-type plasma focus machine, focusing on the technical characteristics. The aim of the upgrade was to improve the performance of the machin...

The ATHENA European University is an alliance of nine Higher Education Institutions with the mission of fostering excellence in research and innovation by facilitating international cooperation. The ATHENA acronym stands for Advanced Technologies in Higher Education Alliance. The partner institutions are from France, Germany, Greece, Italy, Lithuan...

In the current work we report on the generation of acoustic strains in thin ZnO layers using optoacoustic transduction of ultrashort laser pulses into acoustic waves on an Au thin film transducer. After absorption of energy by the electron system of the metal, energy conversion, thermal expansion and mechanical deformation takes place. The generati...

Nano-acoustic strain generation in thin metallic films via ultrafast laser excitation is widely used in material science, imaging and medical applications. Recently, it was shown that transition metals, such as titanium, exhibit enhanced photoacoustic transduction properties compared to noble metals, such as silver. This work presents experimental...

An integrated method, which combines Electronic Speckle Pattern Interferometry, impulse response measurements, finite element method simulations, and psychoacoustic tests, is proposed to evaluate the vibroacoustic behavior of a carbon fiber bouzouki. Three of the carbon fiber instruments are manufactured, and one is qualified via interferometric ex...

The temporal rearrangement of the spectral components of an ultrafast and intense laser pulse, i.e., the chirp of the pulse, offers significant possibilities for controlling its interaction with matter and plasma. In the propagation of ultra-strong laser pulses within the self-induced plasma, laser pulse chirp can play a major role in the dynamics...

The transient acoustic dynamics of a splash cymbal are investigated via the Finite Element Method-Boundary Element Method. Real three-dimensional motion data recorded from the interaction of drummer–drumstick–cymbal provide the initial and the loading conditions to the simulated interaction of the drumstick–cymbal Finite Element Models. Progressive...

In the frame of Horizon Europe EIC-Pathfinder Project TECHNO-CLS: "Emerging technologies for crystal-based gamma-ray light sources", we present the scientific and technological aspects of Dynamical Acoustic Bending (DAB) of crystalline structures for the generation of gamma rays by undulation motion of super-relativistic electron or positron be...

IPPL is one of the access points of the National Research Infrastructure “ELI - LASERLAB Europe Synergy, HiPER & IPERION-CH.gr” (HELLAS-CH) and the leader of the “Fundamental Science Programme” of the ESFRI research infrastructure HiPER. The three main research fields are: i. Laser Matter Interactions, ii. Plasma Science & Technology, iii. Numerica...

The acoustic behaviour of the violin is defined during manufacturing since the vibrational acoustic properties of the instrument are related to the top plate's vibrational modes in a direct way. An important component of the violin assembly is the bridge. The bridge transfers the excitation forces from the strings to the soundboard via the bridge f...

The rapid growth of nanotechnology has increased the need for fast nanoscale imaging. X-ray free electron laser (XFEL) facilities currently provide such coherent sources of directional and high-brilliance X-ray radiation. These facilities require large financial investments for development, maintenance, and manpower, and thus, only a few exist worl...

It was recently demonstrated that a newly explored instability, which was named electro-thermo-mechanical (ETM) instability, was developed in the solid elastic phase in the case of an electrically exploded conductor in the skin effect mode. Here, we present new advances in the exploration of the role of the ETM instability as seed of the magneto-hy...

The temporal rearrangement of the spectral components of an ultrafast and intense laser pulse, i.e., the chirp of the pulse, offers significant possibilities for controlling its interaction with matter and plasma. In the propagation of ultra-strong laser pulses within the self-induced plasma, laser pulse chirp can play a major role in the dynamics...

Laser-induced particle acceleration is a subject of great interest due to its numerous potential applications, among others in Inertial Fusion Energy (IFE) and in biomedical applications (i.e., hadron therapy). In this context, we present research activities using the ZEUS 45 TW femtosecond laser system, hosted at the Institute of Plasma Physics an...

This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles, and explores proton acceleration in the near-critical density regime via magnetic vortex acceleration (MVA). Multiple blast waves (BWs) are generated by laser pulses that compress...

Laser-induced proton acceleration is a subject of great interest due to its numerous potential applications, among others in energy production through Inertial Confinement Fusion (ICF), or in medical applications such as hadron therapy. Extreme pressure gas-jet targets, able to reach the near-critical density (NCR) regime, can be used as high repet...

It is well known that a critical area of concern to inertial confinement fusion (ICF) is target nonuniformities due to their unstable growth. In direct-drive ICF experiments, the process starts when a low intensity pulse illuminates the ablator. Three-dimensional Multiphysics finite element modelling and simulations were recently carried out by our...

The generation of laser based relativistic electron sources involves impressive basic science as well as innovative applications. This study reports first novel qualitative results on polymer-gel radiation dosimetry of ultrafast laser-based relativistic electron beams. The fabricated polymer-gels are irradiated by the ultra-high dose rate (FLASH) l...

Advanced numerical simulations, that include modal and frequency response function finite element analysis, frequency domain and time domain finite element method – boundary element method analysis, are performed to study the vibro-acoustic behaviour of crash and splash musical cymbals. The results of the modal analysis agree well with experimental...

String instruments are complex mechanical vibrating systems, in terms of both structure and fluid–structure interaction. Here, a review study of the modeling and simulation of stringed musical instruments via the finite element method (FEM) is presented. The paper is focused on the methods capable of simulating (I) the soundboard behavior in bowed,...

A relativistic electron source based on high power laser interaction with gas jet targets has been developed at the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University. Initial measurements were conducted using the ‘Zeus’ 45 TW laser with peak intensities in the range of 10¹⁸–10¹⁹ W cm⁻² interacting with a He pulsed gas...

The dynamics of plasmas produced by low current X-pinch devices are explored. This comprehensive computational study is the first step in the preparation of an experimental campaign aiming to understand the formation of plasma jets in table-top pulsed power X-pinch devices. Two state-of-the-art magneto-hydro-dynamic codes, GORGON and PLUTO, are use...

An X-pinch scheme of a low-current generator (45 kA, 50 ns rise time) is characterized as a potential efficient source of soft X-rays. The X-pinch target consists of wires of 5 μm in diameter—made from either tungsten (W) or gold (Au)-plated W—loaded at two angles of 55° and 98° between the crossed wires. Time-resolved soft X-ray emission measureme...

This book collects the lectures presented in the first COST TUMIEE Training School held in Greece in 2019, supplemented with specific applications that illustrate how the multi-scale approach is implemented in specific cases of interest. The book is intended both as a reference in the field and as a textbook for people becoming interested or enteri...

The rapid development of high intensity laser generated particle and photon secondary sources has attracted widespread interest during the last 20 years not only due to fundamental science research but also because of the important applications of this developing technology. For instance, the generation of relativistic particle beams, betatron-type...

The deposition of femtosecond laser optical energy in gases leads to the emission of secondary electromagnetic and acoustic radiation. These optoacoustic components have a complex nonlinear dependency on the laser beam characteristics, such as the pulse energy, duration, wavelength and the focusing conditions, as well as on the optical and elastic...

In this paper we analyze the vibrational behavior of the violin top plate, for varying plate thickness and material properties via finite element method (FEM) numerical simulations. It is well known that the vibrational properties of the top plates of string instruments influence their sound emission characteristics. Due to the impact of global war...

A finite element method (FEM) - boundary element method (BEM) model is developed to compute the sound generated by of a force acting on a circular membrane (drumhead). A vibro-acoustic analysis that combines modal FEM analysis, a FEM steady state dynamic analysis (SSD), considering harmonic loading and boundary element acoustics, is performed. The...

An experimental and numerical study of the nanosecond electrical explosion dynamics of bare and dielectric coated metallic wires in vacuum is reported. A table top Z-pinch generator down-tuned to generate a peak current of 40 kA with a rise time of 60 ns is implemented for the experiments in the skin effect mode. Optical probing diagnostics as well...

The surface roughness and the evolution of its morphology of a pulsed laser irradiated aluminum workpiece, is investigated via numerical simulations and experimental measurements. A three-dimensional transient thermo-structural finite element model is developed to simulate the machining process. The developed finite element material model considers...

A three-dimensional, thermal-structural finite element model, originally developed for the study of laser–solid interactions and the generation and propagation of surface acoustic waves in the macroscopic level, was downscaled for the investigation of the surface roughness influence on pulsed laser–solid interactions. The dimensions of the computat...

The Z-pinch plasma device is a type of plasma confinement system that uses electrical current to generate a magnetic field which compresses a current-carrying wire. In a previous proof-of-principle study, we demonstrated that in the interaction of a single wire with a pulsed current, the generated Electro-Thermo-Mechanical (ETM) instability in the...

Background: During in-office bleaching, appropriate light sources are applied in order to enhance the activity of the bleaching gels applied onto teeth. For this method to be effective, a high absorption of light within the gel is necessary. Variation in the light attenuation capability of the gel, the duration of application and light activation c...

This work presents studies which demonstrate the importance of the very early heating dynamics of the ablator long before the ablation plasma phase begins in laser driven inertial confinement fusion (ICF) studies. For the direct-drive fusion concept using lasers, the development of perturbations during the thermo-elasto-plastic (TEP) and melting ph...

The computational study of x-pinch plasmas driven by pulsed power generators demands the development of advanced numerical models and simulation schemes, able to enlighten the experiments. The capabilities of PLUTO code are here extended to enable the investigation of low current produced x-pinch plasmas. The numerical modules of the code used and...

The Heat Affected Zone - HAZ of a laser irradiated AISI H-13 steel workpiece, is investigated via numerical simulations and experimental measurements. A three-dimensional transient thermo-structural finite element model is developed to simulate the machining process. A Gaussian laser beam is employed as the heat source. The developed finite element...

The Z-pinch plasma device is a type of plasma confinement system that uses electrical current to generate a magnetic field which compresses a current-carrying wire [1,2]. In a previous proof-of-principle study, we demonstrated that in the interaction of a single wire with a pulsed current, the generated Electro-Thermo-Mechanical (ETM) instability i...

We present an integrated study on the scalability and performance of particle-in-cell (PIC) code simulations on CPU and GPU architectures of high parallelization focused on target normal sheath acceleration (TNSA) and laser wakefield acceleration (LWFA) experiments. The developed models follow the experimental specifications of the high-power laser...

Laser-induced breakdown in ambient air by short optical pulses is accompanied by light and sound emission from the excited volume. In this work, these secondary radiative phenomena are jointly studied and their correlation is analyzed and demonstrated both experimentally and analytically. Simultaneous systematic measurements of the light and acoust...

This document describes the collaboration of Dr Jian Fuh Ong from Extreme Light Infrastructure for Nuclear Physics, (ELI-NP), Romania, and Associate Prof. Vasilis Dimitriou, from the Institute of Plasma Physics & Lasers – IPPL of the Hellenic Mediterranean University-HMU in Crete, Greece, which started under the HPC-Europa3 transnational access vis...

The Heat Affected Zone - HAZ of laser irradiated metal workpieces is investigated via numerical simulations and experimental measurements. The influence of the surface roughness of the metal workpieces on the dynamics of the heat affected zone and the induced mechanical strains, are studied. Three-dimensional transient thermo-structural hydrodynami...

Innovative education and training in high power laser plasmas (PowerLaPs) for plasma physics, high power laser matter interactions and high energy density physics: experimental diagnostics and simulations – CORRIGENDUM - Volume 8 - John Pasley, Georgia Andrianaki, Jon Imanol Apiñaniz, Andreas Baroutsos, Dimitri Batani, Emmanouil P. Benis, Andrea Ci...

We study the optimization of collisionless shock acceleration of ions based on hydrodynamic modelling and simulations of collisional shock waves in gaseous targets. The models correspond to the specifications required for experiments with the $\text{CO}_{2}$ laser at the Accelerator Test Facility at Brookhaven National Laboratory and the Vulcan Pet...

The second and final year of the Erasmus Plus programme ‘Innovative Education and Training in high power laser plasmas’, otherwise known as PowerLaPs, is described. The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme, where teaching takes place in five separate institutes with a range of different aims and...

Laser-induced breakdown (LIB) is a well-known phenomenon which leads to plasma generation and rapid production of a large amount of free electrons. The influence of electron gain and loss processes on the breakdown is of significant interest in a wide field of research and industrial applications across science and technology. Because of that, it i...

The Finite Element Method - FEM has been proven to be an ideal numerical scheme for the description of the solid dynamics and phase transitions under laser induced thermal and high-pressure loads. A detailed multiphysics model of the interaction of solid targets with laser pulses is developed to approximate the transition from the solid to the liqu...

High power laser-plasma secondary sources developed at the Institute of Plasma Physics and Lasers-IPPL of the Hellenic Mediterranean University-HMU will be presented. Potential applications of relativistic electron/proton and X-ray secondary radiation beams will be discussed. Representative results are demonstrated focused on biomedical application...

In this presentation, physical and technical aspects of laser-sound generation, a novel technique for reproducing continuous and controlled sound via laser-induced breakdown (LIB) in air, are discussed. Laser-generated sound waves (LIB acoustic pulses) are generally N-shaped and their frequency spectrum extends from the low frequencies of the audib...

High intensity laser induced particle acceleration is a subject of great interest due to its numerus applications such as energy production by inertial confinement fusion - ICF as well as medical applications like hadron therapy. Particle acceleration is achieved mainly by Target Normal Sheath Acceleration – TNSA and Laser Wake Field Acceleration -...

Simulations of the experimental research activities in IPPL

The machinability of a steel workpiece through conventional and Laser-Assisted Machining (LAM) is studied by the help of the Finite Element Method (FEM). In LAM, the laser beam is applied as a heat source to ensure sufficient local heating of the workpiece at a certain distance from the cutting tool and the machinability of materials is increased s...

The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light...

Numerical modelling and simulations | Experimental validation methods | Additional data | Future research on the seeding mechanisms of plasma instabilities

The 45 TW Zeus laser at the Centre for Plasma Physics and Lasers of the TEI of Crete at Rethymno, Greece is used to generate secondary sources of electrons, ions and neutrons as well as X-rays with applications to medical physics, radiation testing and homeland security applications. The interaction of the intense electric field of the laser create...

The Erasmus Plus programme ‘Innovative Education and Training in high power laser plasmas’, otherwise known as PowerLaPs, is described. The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme where teaching takes place in five separate institutes with a range of different aims and styles of delivery. The ‘in cl...

Femtosecond laser pulses are used for the excitation of surface acoustic waves (SAWs) in a gold thin film transducer deposited on a glass substrate, while a single longitudinal nanosecond laser source is employed for their full-field, high-resolution dynamic interferometric imaging in a pump–probe experimental set-up. The successful combination of...