Action Of Ultrashort Laser Pulse Research Articles

Modeling of a heat source in a film with nanoparticles under the action of ultrashort laser pulses

Modeling of a heat source in a film with nanoparticles under the action of ultrashort laser pulses

Investigation of material heating under the action of ultrashort laser pulses

The aim of this work was to study the heating of an AISI 304 plate in the ablative mode of femtosecond laser pulses. The variable parameter was the change in the speed of movement of the laser beam over the treated surface. The paper presents the results of measuring the heating temperature of the sample surface exposed to laser radiation without scanning laser radiation with different pulse energies. The results of the dependence of the heating of the material surface on the speed of movement of the laser radiation with a constant number of acting pulses are presenting.

Лазерно-индуцированные люминесцентные центры в алмазе: влияние экспозиции и длительности ультракоротких лазерных импульсов

The optical properties of point luminescent centers formed in the volume IaA-type natural diamond under the action of ultrashort laser pulses in the visible range (515 nm) with durations of 0.3–2.4 ps were investigated. The analysis using confocal Raman spectroscopy demonstrates the formation of nitrogen vacancy centers (NV) and there are no graphitization traces in processing areas. The luminescence amplitude of NV centers depends linearly on the exposure time at different durations of ultrashort laser pulses.

Laser-induced luminescent centers in diamond: influence of exposure and duration of short laser pulses

The optical properties of point luminescent centers formed in the volume IaA-type natural diamond under the action of ultrashort laser pulses in the visible range (515 nm) with durations of 0.3-2.4 ps were investigated. The analysis using confocal Raman spectroscopy demonstrates the formation of nitrogen vacancy centers (NV) and there are no graphitization traces in processing areas. The luminescence amplitude of NV centers depends linearly on the exposure time at different durations of ultrashort laser pulses. Keywords: ultrashort laser pulses, luminescence, luminescent centers in diamond, NV centers.

Electron thermal conductivity of nickel and aluminum in solid and liquid phases in two-temperature states

Analytical expressions for the electron thermal conductivity of nickel and aluminum are presented. The thermal conductivity depends on the electronic and ionic temperatures, density and phase of the substance (solid or liquid). The expressions obtained can be used in hydrodynamic calculations of the ablation of these metals or multilayer targets made from them. We consider the case when ablation is caused by the action of ultrashort laser pulses.

Ultrafast electron dynamics and energy deposition during IR-visible femtosecond laser ablation of fluorite

The action of ultrashort laser pulses on dielectrics leads to the processes of redistribution of the laser pulse energy in the interaction region. The mechanisms of ultrafast energy deposition and the electron dynamics under the action of ultrashort laser pulses determine the type of final structures or elements in the transparent dielectrics. One type of these elements is a birefringent nanogratings formed with an orientation perpendicular to the laser radiation. In this work, laser-induced birefringent structures in calcium fluoride (CaF2) bulk were obtained under the action of tightly-focused laser pulses with durations 0.3-3.8 ps and wavelengths of 515 and 1030 nm. Birefringence in modified region was analyzed using polarization contrast optical microscope with Abrio imaging system.

Many-electron effects in secondary radiation generation during the interaction of atoms with intense laser pulses

A parallel program has been developed for numerically simulating the interaction of intense laser pulses with many-electron atoms based on non-stationary Kohn–Sham equations. With the use of this program, we calculate the nonlinear electron currents excited during ionization of argon atoms by intense two-color laser pulses. Based on the comparison with the solution of the time-dependent Schrödinger calculations for hydrogen atoms, the importance of taking into account many-electron effects in simulating the generation of secondary radiation in atomic gases under the action of ultrashort laser pulses is shown.

Formation of Coatings under the Action of Laser Radiation in Liquid Media

The influence of the chemical composition of the substrate material on the chemical and phase composition of the formed coating was investigated. A number of experiments aimed at studying the interaction of titanium alloys with ultrashort laser pulses in different reaction media was carried out. A new method for the formation of titanium carbide under the action of ultrashort laser pulses on the surface of a titanium sample in a liquid hydrocarbon and liquid nitrogen medium is described. The description of the experiment is presented. The treated surface was investigated using a scanning electron microscope. Raman spectra from the surface of treated titanium alloys under different exposure conditions are obtained.

Formation of powder materials under the combined influence of pulse laser radiation and electric arc discharge

In this paper presents an assessment of the efficiency of the synthesis of nanoscale spherical powder materials by the combined action of ultrashort laser pulses and electric arc discharge. Experimentally determined optimal from the point of view of technological effectiveness and efficiency, the conditions conducive to the spread of eclectic arc discharge by laser-induced plasma channel. The scheme of experimental work, the results achieved.

Laser-induced angular momentum of spheroidal metal nanoparticle in a medium

A theory for the generation in a spheroidal metallic nanoparticle of an angular momentum under the action of ultrashort laser pulse is developed. We proposed the mechanism for generation of rotation force associated with nanoparticle polarization in the frequency region close to the surface plasmon resonances. Under illumination of the laser field the nanoparticle with an asymmetrical shape is polarized and becomes a dipole. The pair of electric field forces tends to turn the dipole along the field direction. As a result, the angular momentum arises. It is considered that the polarization becomes a tensor quantity for the nanoparticle sizes smaller than the electron mean free path in it. It is shown that the rotation direction can be controlled by varying the wavelength of the incident light. The expressions for the components of the polarization tensor and for the angular momentum of a spheroidal metal nanoparticle are obtained.

Femto-, Picosecond, and Terahertz Optoacoustics

The possibilities offered by the optoacoustic monitoring of the sea shelf are considered, based on the development of reliable laser sources of femto- and picosecond pulse duration and new ways of detecting and processing high-frequency signals. The basis of these new possibilities is a volume source of sound produced as a result of the breakdown of the medium under the action of ultrashort laser pulses. An overview of new worldwide achievements is presented. The results from a number of model experiments on the optoacoustic monitoring of low concentrations of gas impurities, and on the precise monitoring of the sea shelf, are interpreted.

Metal film on a substrate: Dynamics under the action of ultrashort laser pulse

The movement of metal film placed on a glass substrate under action of ultra-short laser pulse is studied with using of two-temperature hydrodynamic calculations. The features of the oscillatory modes of movement of the film on the substrate under the influence of low-energy laser pulses are investigated. Transition from film delamination from the substrate as a whole to break of a film and flying away only a forward layer of a film is tracked at growth of the enclosed energy.

Blistering of film from substrate after action of ultrashort laser pulse

The goal of the paper is to explain experimental results concerning film blistering. Tightly focused diffraction limited ultrashort optical laser pulse illuminates a small spot at a surface of a thin metal film mounted upon a dielectric or semiconductor support (substrate). Film mechanically separates from substrate and form a cupola like bump in a rather narrow range of absorbed fluences. Below this range deformations inside the spot are negligible. While above the range the hole remains in a film in the irradiated spot. The paper presents physical model starting from absorption and two-temperature state and including, first, description of conductive redistribution of absorbed heat, melting, hydrodynamics of strong three-dimensional deformations of a moving film, and, second, freezing of molten metal.

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)($2\ifmmode\times\else\texttimes\fi{}2$):CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, ``hot adsorbate'' formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.

Formation of a fine-dispersed liquid-metal target under the action of femto- and picosecond laser pulses for a laser-plasma radiation source in the extreme ultraviolet range

We report the results of studying the dynamics of deformation and fragmentation of liquid-metal droplets under the action of ultrashort laser pulses. The experiments have been performed to optimise the shape of the droplet target used in extreme ultraviolet (EUV) radiation sources based on the laser-produced plasma using the pre-pulse technology. The pre-pulse is generated by a system incorporating a master Ti : sapphire oscillator and a regenerative amplifier, allowing one to vary the pulse duration from to . The power density of laser radiation at the droplet target, averaged over the pulse duration and spatial coordinates, has reached . The production of liquid-metal droplets has been implemented by means of a droplet generator based on a nozzle with a ring piezoceramic actuator. The droplet material is the eutectic indium – tin alloy. The droplet generator could operate in the droplet and jet regime with a maximal rate of stable operation 5 and , respectively. The spatial stability of droplet position of its diameter is achieved. The size of the droplets varied within , their velocity was depending on the operation regime.

Investigation and control of ultrafast laser-induced isotropic and anisotropic nanoscale-modulated index patterns in bulk fused silica

Ultrafast laser-induced refractive index changes in a-SiO2 consist, depending on the irradiation conditions, of either positive variations, voids, or regular nanoscale patterns, each of these underlying specific structural transformations. These allow for obtaining a large palette of optical functions ranging from low loss guiding to anisotropic scattering. While briefly reviewing the excitation mechanisms, we spectroscopically interrogate local electronic and structural transformations of the glass in the isotropic index zones and in the regular self-organized nanostructures, indicating bond breaking and matrix oxygen deficiency. A spatial defect segregation marks the material transformation in the different photoinscription regimes. We equally propose a method of real time control of nanogratings formation under the action of ultrashort laser pulse with variable envelopes. Application as polarizing optical devices is discussed.

Diffusionless oxidation and structure modification of thin Cr films by the action of ultrashort laser pulses

Results of impact on Cr thin metal films by ultrashort laser pulses are investigated in the paper. For the first time thermochemical action of such pulses is shown and confirmed by analytical approaches (micro-Raman spectroscopy, CAES and others) and selective chemical etching both. It is impossible to ascribe this effect to well-known mechanism of heterogeneous diffusion at the irradiation specified conditions. Possible reasons of Cr thin films diffusionless oxidation and structure modification are observed. Discovered phenomena open up new opportunities for developing of optical thermochemical data recording on Cr thin films, which are widely used in microelectronics as photomasks and in the process of diffractive optical elements manufacturing.

Control of ultrafast laser-induced bulk nanogratings in fused silica via pulse time envelopes

Employing a method of in-situ control we propose an approach for the optimization of self-arranged nanogratings in bulk fused silica under the action of ultrashort laser pulses with programmable time envelopes. A parametric study of the influence of the pulse duration and temporal form asymmetries is given. Using the diffraction properties of the laser-triggered subwavelength patterns we monitor and regulate the period and the quality of the periodic nanoscale arrangement via the effective nonlinear excitation dose. Periodicity tuning on tens of nanometers can be achieved by pulse temporal variations, with a minimum around 0.7 ps at the chosen powers. Equally, strong sensitivity to pulse asymmetries is observed. The driving factor is related to increasing carrier densities due to nonlinear confinement and the development of extended nanoroughness domains upon multiple exposure, creating a pulse-dependent effective accumulation dose via a morpho-dimensional effect. The result may impact the associated optical functions.

Ablation of insulators under the action of short pulses of X-ray plasma lasers and free-electron lasers

An experimental and theoretical study has been carried out of the ablation of a solid insulator with a wide band gap (LiF) under the action of ultrashort laser pulses of the UV range, obtained in a free-electron laser (pulse width τ<sub>L</sub>=0.3ps, photon energy ħω<sub>L</sub>=20.2eV), and the soft X-ray region, obtained in a silver-plasma laser (τ<sub>L</sub>=7ps, ħω<sub>L</sub>=89.3eV). A comparison is made of the results obtained on the two laser systems. It is shown that the ablation threshold is about the same for both lasers. A theory is presented that explains the weak growth of the ablation mass with increasing surface energy density of the laser radiation (the fluence) in the case of X-ray lasers as a result of the transition from spallation close to the ablation threshold to evaporative ablation at high fluence values.

Acoustic probing of two-temperature relaxation initiated by action of ultrashort laser pulse

Ultrashort laser pulse transfers metal into a two-temperature warm dense matter state and triggers a chain of hydrodynamic and kinetic processes—melting, expansion, stretching, creation of tensile stress and transition into metastable state. We study the response of aluminum film deposited on a glass substrate to irradiation by a pump laser pulse transmitted through glass. Several films with thicknesses from 350 to 1200 nm have been investigated. The smallest thickness is of the order of the heating depth dT∼100 nm in Al. The dT-layer and the free rear side of the film are coupled through pressure waves propagating between them. Therefore, the processes within dT-layer affects the time dependent displacement Δxrear(t) of the rear surface. We compare simulated and experimental dependencies Δxrear(t) obtained by the pump–probe technique. It allows us to define a thickness of molten Al layer and explore the two-temperature processes occurring inside the heated layer.