Laser-induced Phenomena Research Articles

Numerical study of ultrafast optical instability causing structured light absorption in metal

We present the first-principle numerical study of nonlinear decay of a femtosecond laser pulse into a pair of surface plasmon polaritons (SPP) during reflection from a rough metallic surface. The ultrafast dynamics of the decay was studied at damaging laser fluences of about 1 J/cm2, and the principal role of the electronic collision rate growth was proved. The resulting strongly inhomogeneous heating of metal is an important stage of laser-induced phenomena like ablation, terahertz radiation generation, and periodic surface structures formation.

X-ray Self-Emission Imaging of Hydrodynamic Laser-Induced Astrophysical Phenomena

In this article, we present an overview of the application of X-ray self-emission methods for the imaging of hydrodynamic astrophysical phenomena in laboratory-scale experiments. Typical diagnostic approaches, their advantages, drawbacks, and application perspectives are considered. We show that X-ray imaging and spectroscopy methods with 2D and even 1D spatial resolution are valuable for numerous laboratory astrophysical problems. Furthermore, the methods revealed the hydrodynamic evolution, the spatial shape and structure, and spatial features of important parameters such as electron density and plasma temperature of astrophysical objects and related phenomena, which are also required for the verification of astrophysical models.

Laser-power dependence effects on the structural stability of nanocomposite catalysts studied by Raman spectroscopy: On the structure-activity correlations in glycerol acetylation

Structural properties of binary CeAl, CeMn, NiAl, CeZr, SnTi and ZrMn nanocomposite oxide catalysts were monitored towards the Laser Raman spectroscopy investigations providing new insights to control catalytic applications upon temperature ranges at which the laser power was varied. The lattice vibrational properties were investigated by varying the incident laser power during Raman measurements from 0.017 mW to 4.0 mW. Structural changes in nanocomposites were achieved upon increasing laser power, which induced local heating disorder causing the sintering of CeMn, SnTi, and ZrMn nanocomposites. The laser-power dependence effects on the structural stability of CeAl, NiAl, and CeZr were observed with high amounts of oxygen vacancy defects over CeAl upon laser power heating. Both CeMn and ZrMn exhibited phase transitions from MnO2 to α-Mn2O3 being the use of the latter nanocomposites limited to work at 1.1 mW. The structure-activity correlations for the nanocomposite oxide catalysts were evaluated through the acetylation of glycerol with acetic acid reaction to produce valuable acetins. Remarkable shifts in the Raman bands wavenumbers and other spectral changes in the lattice mode were caused by laser-induced phenomena accounting for the undesired phase formation and particle growths, as well. This resulted in a low catalytic performance of the NiAl, SnTi, CeMn and ZrMn owing to the thermal effects. Contrary, CeAl and CeZr were more active for acetins products avoiding the phase transformations due to their structural stability at high temperatures, which in turn avoided leaching of the active Ce sites during the reaction.

Nanosecond laser shock detonation of nanodiamonds: from laser-matter interaction to graphite-to-diamond phase transition

Nanodiamonds (NDs) have been widely explored for applications in drug delivery, optical bioimaging, sensors, quantum computing, and others. Room-temperature nanomanufacturing of NDs in open air using confined laser shock detonation (CLSD) emerges as a novel manufacturing strategy for ND fabrication. However, the fundamental process mechanism remains unclear. This work investigates the underlying mechanisms responsible for nanomanufacturing of NDs during CLSD with a focus on the laser-matter interaction, the role of the confining effect, and the graphite-to-diamond transition. Specifically, a first-principles model is integrated with a molecular dynamics simulation to describe the laser-induced thermo-hydrodynamic phenomena and the graphite-to-diamond phase transition during CLSD. The simulation results elucidate the confining effect in determining the material’s responses to laser irradiation in terms of the temporal and spatial evolutions of temperature, pressure, electron number density, and particle velocity. The integrated model demonstrates the capability of predicting the laser energy threshold for ND synthesis and the efficiency of ND nucleation under varying processing parameters. This research will provide significant insights into CLSD and advance this nanomanufacturing strategy for the fabrication of NDs and other high-temperature-high-pressure synthesized nanomaterials towards extensive applications.

Recent Research and Development Status of Relaxed Optics and Laser Technology: A Review

It is shown that for laser technologies it was necessary to create a new branch of physics: Relaxed Optics (synthesis of methods of the physical optics, quantum electronics, physical chemistry, physics of irreversible phenomena in unitary system). It is allowed to explain complex chain processes of interaction light and matter. Possible applications of Relaxed Optical methods for the modeling of the laser-induced processes phenomena, including laser implantation (surface and subsurface processes), laser-induced optical breakdown (volume processes) and laser annealing of radiation and other defects in solid, are discussed. Perspectives of using these methods for the creation of new laser technologies, including creation new types of optoelectronic devices (heterostructures, diffraction lattices, etc.), resolution the problems of metallurgy, material science, painting, architecture and a building, are analyzed.

Attosecond light source in material science investigation

Since the dawn of the 21st century, attosecond (1 as =10–18 s) science has been explored and is now fast developing. It brought us the unprecedented time-resolved spectroscopy of quasiparticle dynamics in materials. To date, femtosecond (1 fs =10–15 s) time-resolved pump-probe technology is widely used to study the ultrafast quasiparticle dynamics of quantum materials, such as strong correlated quantum materials, topological materials, superconductors, and semiconductors. In a typical pump-probe experiment, the laser source will be divided into two beams, namely the pump and the probe beams. The pump beam excites the quasiparticles in target materials, and the time-delayed probe beam scans the ultrafast dynamics of the excited state carriers and the coherent lattice vibrations. By employing this method, we are able to observe the lifetimes due to various interactions, such as the electron-electron scattering, electron-phonon coupling, phonon-phonon scattering, etc. By manipulating the various laser pulse characteristic parameters, such as the photon energy, polarization, pulse duration and laser fluence, femtosecond ultrafast spectroscopy excels in investigating the physical properties of materials, which are largely determined by the outer electrons. To investigate the excited states of various materials, femtosecond pump-probe spectroscopy is often conducted under extreme conditions, such as low temperature, strong magnetic field, and high pressure. As a comparison, attosecond ultrafast spectroscopy can not only get access to exploring even faster ultrafast processes, but also probe the inner shell electrons of various types of materials. Attosecond pulses are usually prepared by high-order harmonic generation (HHG). The most common way of generating HHG is in an atomic gas. The excited unbound electrons are accelerated to the nuclei, and the electron-core collisions lead to multiple ionizations. The photons are emitted as trains of ultra-shot pulses. Recently, HHG has also been realized in liquids and solids. The separation of isolated attosecond pulses from trains of attosecond harmonics can be achieved by manipulating the polarization gating, the ultrashort few-cycle driving lasers, or both. Both attosecond pulse trains and isolated attosecond pulses can be applied to the investigation of quantum materials. With the aid of attosecond time-resolved ultrafast pump-probe spectroscopy, more and more fundamental physical properties and relevant applications will be revealed, which will greatly lead the development of condensed matter physics, material sciences, and their applications. Conversely, the attosecond science and technology can also benefit from the deeper understanding of the physical properties of solid state materials. In this article, we first introduce two types of attosecond time-resolved pump-probe experimental techniques, attosecond transient absorption spectrum (ATAS) and attosecond time-resolved angle-resolved photoemission spectroscopy (atto-ARPES). We review typical experiments carried out using such facilities in dielectrics, semiconductors, layered materials, transition metals, etc., and make an outlook for the potential applications of attosecond laser spectroscopy in this field of material science. Furthermore, as the attosecond pulses are often generated from the HHG of mid-infrared laser beams, the mid-infrared ultrafast spectroscopy itself can also be applied to material investigations. Moreover, we review the applications of mid-infrared ultrafast spectroscopy in condensed matter physics, with intriguing laser-induced novel phenomena.

Lower-Threshold Ionization in Laser Channel Propagation

The paper considers the creation of long ionized channels in atmospheric aerosol based on the combustion and detonation processes. The literature review is performed in this field. Special attention is given to the different laser-induced threshold phenomena affecting gas-dispersion systems.

Enhancement of high reflectivity mirrors using the combination of standard and sculptured thin films

The total generated output power in high-power laser systems is mainly limited by the laser-induced damage phenomena in coated optics. A significant part of optics include high reflectivity coatings. A research was conducted for the development of advanced high reflectivity mirrors, capable to withstand extreme laser fluence and featuring spectral stability at different ambient conditions. A concept of combination of IBS and GLAD technologies was proposed and implemented to form a hybrid multilayer mirror for the 355 nm wavelength. An optical and structural properties were investigated to evaluate the advantages of both technologies. The relation between the number of sculptured silica layers and standard mirrors performance under the high power of laser radiation was determined. The results of analysis show an improved reflectivity and optical resistance of consolidated coatings. LIDT measurements indicate the potential of reaching 90 J/cm2 for 355 nm wavelength (pulse duration 2.5 ns) while maintaining the reflectivity value higher than 99.5%. New findings indicate the superiority of hybrid coatings if compared to both classical and all-silica coatings. This knowledge opens up the new possibilities in further development of extreme light sources.

Laser-induced optical photobleaching in Bi-doped Ge30Se70 amorphous thin films

The paper reports the photo-induced effects on the optical and structural properties of ternary Ge30Se70−xBix (x = 5, 10) thin films illuminated with 532 nm green laser light. The material exhibits photo-bleaching nature when exposed to laser light for a prolonged time. The amorphous nature sustains after laser irradiation as detected by X-ray diffraction. The chemical composition of the deposited thin film was examined by energy dispersive X-ray analysis. Field emission scanning electron microscopy investigation showed that the surface morphology was influenced by the laser irradiation. The transmission spectra were collected from UV–Vis-NIR spectroscopy which shows the films exhibit indirect allowed transition. The other optical parameters were calculated from the transmission spectra. The linear optical properties were influenced by the laser-induced phenomena. The photobleaching is explained on the basis of homopolar bond breaking and formation of heteropolar bonds with photon energy. The Raman spectra provided the evidence of photo structural changes in the films.

Tuning of dielectric properties in Se78Te20Sn2 glass using UV–Vis-IR lasers

Laser-induced phenomena in Chalcogenide Glasses (ChGs) are the issues of the systematic investigations with a view of better perceptive of the mechanism behind such effects as well as its practical applications. In fact, the study of the photo-induced effects in ChGs is still an on-going research activity. The present paper reveals the observation of photo-induced dielectric effects in ternary Se78Te20Sn2 (STS) ChG. We have developed a novel method to achieve a distinctive photo-induced effect in a second generation ChG by employing cw-laser sources of four different wavelengths. Our results show the demonstration of photo-dielectric effects in electrical properties (dielectric constant/loss and a. c. conductivity) of ternary STS ChG. A tentative explanation is also proposed for the observed effects.

Selected laser-induced plasma spectroscopy: From medical to astrophysical applications

This work discusses laboratory experiments using atomic and molecular spectroscopy for diagnosis of laser-induced phenomena of interest in the field of medicine, and in astronomy for the understanding of recorded spectra from selected stars. Photo-acoustic spectroscopy utilizes femtosecond laser-pulse trains for diagnostic and therapeutic applications. Optical emission spectroscopy explores nominal nanosecond laser-induced, nano-particle plasma and its detection sensitivity. The study of laboratory plasma generated in selected gas-mixtures reveals insights for the interpretation of white dwarf spectra.

Modelling laser-induced heat transfer phenomena of thin-films using OpenFOAM

• A Finite Volume (FV) Model for simulating laser annealing of thin-film based structure. • Experimental validation of the OpenFOAM-based conjugate heat transfer model. • Detailed understanding of the diode laser-induced thermal and optical phenomena of the multilayer structures. • A guideline for optimising and designing of thin-film based architecture. This paper presents a numerical simulation model for analysing diode laser-induced thermal phenomena on high absorbing thin-films. Continuous wave (CW) diode laser, in the form of millisecond annealing, is a promising tool for processing of the high absorbing thin-film based solar cells. The localised nature of laser processing, in one hand, gives an opportunity to heat the film to a higher temperature over a much shorter time than the conventional methods, while, on the other hand, allowing the substrate to remain at low temperature with a low ramp-up rate. Also, unlike the laser processing in pulse mode, the CW diode laser can heat the high absorbing thin-films over a longer period without initiating melting and dwetting. Since the CW diode laser-induced thermal treatment is entirely characterised by its parameters, the inappropriate setting of its parameters may lead to a negative effect on the absorber layer . In view of these, being highly a thermal process, the basic understating of the CW diode laser annealing of high absorbing thin-film is necessary, which arguably may not be possible using the experimental techniques. Numerical simulations, in this case, offer the possibility to acquire knowledge of the process; hence, in this contribution, a numerical model has been developed in an open-source based computational fluid dynamics (CFD) platform, known as OpenFOAM. Upon development of the model, its prediction has been compared with the experimental results of the CW diode laser annealing of silicon thin-film on the glass substrate , in which an excellent agreement with the experimental results has been observed. In the second part of this study, the developed numerical model has been implemented to reveal the CW diode laser-induced thermal phenomena of the high absorbing CZTS thin-films, which is considered as deposited on Molybdenum (Mo) coated glass substrate, a typical structure used for designing of CZTS thin-film based solar cells. Although CZTS thin-film is considered as the ideal material for using as an absorber in the next generation thin-film based solar cells, its behaviour in the case of CW diode laser-induced thermal treatment has not been understood yet. Hence, the present study may likely to contribute to the processing and optimising of the CZTS thin-film based structure.

Effective Defect Passivation by Hydrogen Using a Laser Light Source

This paper presents a detailed investigation of the effect of a diode laser-induced thermal process on the hydrogen passivation of boron–oxygen (B–O) defects using numerical modelling. A state-of-the-art numerical model is developed using OpenFOAM based on a finite volume approach. The model considered dissociation, formation and passivation of the B–O defects including four reaction kinetics, and solved the coupled thermal equations and kinetic models. The developed model is then applied to elucidate the influence of passivation, as well as the formation of a B–O defect complex using laser-induced thermal phenomena by varying the key parameters of laser power and exposure time. The results reveal some interesting insights on how the hydrogen evolves out of the B–O defect sites, in the form of dissociation, when the exposure time is higher than 20 s, and hence affect the hydrogenated defect passivation process.

Plasma emission during time-resolved laser-induced incandescence measurements of aerosolized metal nanoparticles

There has been speculation that several commonly observed anomalies in time-resolved laser-induced incandescence (TiRe-LII) measurement data may be caused by bremsstrahlung emission from a laser-induced plasma, a phenomenon known to occur at higher fluences typical of laser-induced breakdown spectroscopy. This paper presents the first theoretical framework to investigate a laser-induced plasma formation under LII measurement conditions, and explores how this plasma may affect time-resolved spectral intensity measurements. At fluences greater than 0.8 J/cm2, the absorption cross-section of the laser-energized nanoparticle is enhanced due to inverse bremsstrahlung absorption, and bremsstrahlung emission results in an overestimation of the nanoparticle temperature due to the corruption of the incandescence signal. Under these conditions, neutral bremsstrahlung emission is more prevalent than electron–ion bremsstrahlung due to the weak nature of the induced plasma. Nevertheless, the current model does not predict laser-induced plasma phenomena below ~ 0.5 J/cm2, typical of low-fluence TiRe-LII measurements.

One-shot time-resolved holographic polarization microscopy for imaging laser-induced ultrafast phenomena

A time-resolved holographic polarization microscopy, based on angular multiplexing holographic technique, is proposed for imaging ultrafast phenomena in polarization-sensitive transparent materials. This method can retrieve and image the complex amplitude distributions of two orthogonal polarization components of two sequential vector wavefronts with ultrashort time interval by a single short recording. Some experimental results for imaging the pulse laser induced ultrafast events based on the method are given. It is demonstrated that this technique may provide a potential tool for characterizing ultrafast processes in polarization-sensitive materials, especially in the non-reproducible experiment conditions.

Spatial-domain interferometer for measuring plasma mirror expansion.

We present a practical spatial-domain interferometer for characterizing the electronic density gradient of laser-induced plasma mirrors with sub-30-femtosecond temporal resolution. Time-resolved spatial imaging of an intensity-shaped pulse reflecting off an expanding plasma mirror induced by a time-delayed pre-pulse allows us to measure characteristic plasma gradients of 10-100nm with an expansion velocity of 10.8nm/ps. Spatial-domain interferometry (SDI) can be generalized to the ultrafast imaging of nm to μm size laser-induced phenomena at surfaces.

Thermoelastic Model for Impulsive Stimulated Scattering Monitoring the Evolution from Capillary to Rayleigh Type Wave Propagation on the Surface of Viscoelastic Materials Throughout the Glass Transition

In recent decades, the impulsive stimulated scattering (ISS) method, which is based on photothermal and photoacoustic phenomena, has been successfully used to simultaneously investigate the thermal and elastic properties in a four-wave mixing configuration, both in transmission in semitransparent materials and on reflecting surfaces of solids. In this report, an extension of the technique is proposed to study a laser-induced thermoelastic response at the free surface of glass-forming liquids. The employed all-optical configuration allows extraction of information about the acoustic shear modulus in the MHz frequency range, and hence is complementary to the classical ISS configuration in the transmission mode, which is suitable to study the relaxation of the longitudinal acoustic modulus, and to another earlier reported ISS configuration, which is exciting and probing laser-induced thermoelastic phenomena at a liquid–solid interface. A theoretical model is presented and numerically illustrated for the glass transition of glycerol, and experimentally validated for water at room temperature.

Two-dimensional measurements of laser-induced breakdown in air by high-speed two-frame shadowgraphy

We present two-dimensional measurements of the laser-induced plasma development and shock wave evolution in air. The breakdown is induced by a Q-switched Nd:YAG laser (λ=1064 nm) with a pulse duration of 4 ns. To study these fast laser-induced phenomena, we have developed a high-speed, two frame shadowgraph method. It enables 2D visualization of a laser-induced event in two time instances, which are delayed by an arbitrary time interval in the range from 300 ps to 30 ns. The established method is based on 30 ps, green (λ=532 nm), and linearly polarized laser pulse, which is split into two orthogonally polarized illumination pulses for direct and delayed illumination of the breakdown area. Exploiting polarization of the probe pulses, we capture two temporally and spatially separated frames with two CCD cameras. Special attention is given to the subsequent data processing, especially to the minimization of the systematic error due to alignment of both images, and to the determination of 2D velocity distribution from the captured image pairs.

Variation in the Etch Rate of LIBWE Fabricating Deep Microtrenches

were fabricated with a fluence of 1.3 J/cm 2 , a pulse repetition of 80 Hz, and various pulse numbers. Special care was directed to maintaining in-focus conditions for etching. In the fabrication of 5-µmwide microtrenches, etch rates of 5.3 nm/pulse evaluated for trenches with depths of less than 4 µm increased by a factor of 2.55 to 13.5 nm/pulse when the trenches became deeper than 16 µm. Such variation in the etch rate reduced with width and became negligibly small for 20-µm-wide microtrenches. Based on a similar dependence on width, the variation in etch rate with depth can be related to the size effect observed in LIBWE. As a factor causing the size effect as well as the variation in etch rate with depth, the interaction between the laser-heated surface and the solution in an early time region of the laser-induced phenomena is proposed.

Laser-Induced Backside Wet Etching Employing Green DPSS Laser and Liquid Metallic Absorber

An indirect laser processing, laser-induced backside wet etching (LIBWE) is one of effective techniques for flexible laser-direct-write (LDW) type micromachining of transparent materials. Micromachining by LIBWE employing a diode-pumped solid state (DPSS) green laser and a galvanometer-based point scanning system was examined with employing organic dye solution and liquid metal as laser-absorbing media. LIBWE using liquid metal absorber showed smaller threshold pulse energies for etching (9.1 μJ/pulse) than that using organic dye solution (33 μJ/pulse). Different morphologies of etched surfaces were observed for different laser-absorbing media, indicating different mechanisms involved in the etching processes. The laser-induced dynamic phenomena were investigated by means of transient reflection measurements. The different contribution of direct and indirect actions of laser pulses was indicated for LIBWE employing different laser-absorbing media.