Femtosecond Laser-matter Interactions Research Articles

Effects of fs pulsed laser ablation on synthetic zeolite targets

With the aim to perform nanozeolite re-crystallization by laser treatment, the effects of Femtosecond Pulsed Laser Ablation (fs PLA) on three different targets of zeolite with LTA typology (zeolite A) were investigated. One sample of zeolite A was formed by modified standard IZA protocol (LTA). The other two were synthesised with the addition of red mud (RMFe-LTA) or nanomagnetite (NMFe-LTA) during the hydrothermal process. All the ablated targets were analysed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results indicate that differences in chemical composition of the targets, together with the local temperature gradient determined by femtosecond laser-matter interaction occurring under high to middle-low pressures, have a significant influence on mineral and morphology changes of starting raw minerals as well as on evolution of reduction reactions. This is due to fast heating and cooling down processes inducing in turn different re-solidification characteristics mainly on RMFe-LTA and NMFe-LTA targets.

Femtosecond laser–matter interaction of tungsten carbide

We investigate the femtosecond laser-matter interaction for a tungsten carbide with 10% of cobalt. A femtosecond laser (1030 nm) with a pulse duration of 400 fs was used. For cumulated fluences between 1.4 and 4J/cm2, laser-induced periodic surface structures (LIPSS) could be produced with a low ablation rate. LIPSS had a spatial period of 665 nm and an amplitude of 225 nm. The athermal ablation threshold fluence ranged from 0.35 to 11J/cm2 in cumulated fluence for a range between 1 and 100 pulses. Thus, dimples could be fabricated without any thermal effects. In addition, the incubation coefficient and optical penetration depth of tungsten carbide were determined. They were equal to 0.79 and 19 nm, respectively.

Comparison of 1030 nm and 257 nm wavelengths for U-Pb zircon dating by femtosecond laser ablation – Inductively coupled plasma mass spectrometry with support of 3D crater imaging

Femtosecond near-infrared (NIR, 1030 nm) and near-ultraviolet (NUV, 257 nm) laser ablation (fs-LA) were evaluated for U-Pb dating of zircons using inductively coupled plasma mass spectrometry (ICP-MS). The apparent ages are in agreement with the reference ages, within expanded combined uncertainties, at both wavelengths, but NIR fs-LA produces poorer uncertainties and a ≈ 3.5% bias on the reference age of Mudtank and Plešovice zircon. The time resolved 238U signal intensity rises sharply and progressively decreases in NUV, whereas patterns in NIR follow progressive increase and then decrease during ablation. Synchrotron X-ray micro-tomography (XRMT) imaging of an ablated quartz permitted to link the morphology and dimensions of fs-LA craters to the performances of fs-LA-ICP-MS analyses on zircons. Average ablation rates are similar at 3 J.cm-2 for both wavelengths. However, the ablation rate is higher in NIR at 7 J.cm-2 than in NUV at 2 J.cm-2, whereas the fs-LA-ICP-MS yield (in counts.shot-1.ppm-1) is lower in NIR at 7 J.cm-2 than in NUV at 2 J.cm-2. This paradox as well as the biased or imprecise fs-LA-ICP-MS analyses are explained by nonlinear shot-to-shot ablation in NIR compared to NUV, induced by: (i) catastrophic ablation, (ii) incubation effects, and, to a minor extent (iii) preferential ionization of U relative to Pb. Consequently, NIR fs-LA is capable of producing accurate U-Pb ages thanks to the properties of femtosecond laser matter interactions, but with a higher fluence, sample consumption and poorer statistics than those obtained with NUV fs-LA.

Single-shot ultrafast visualization and measurement of laser-matter interactions in flexible glass using frequency domain holography.

We perform single-shot frequency domain holography to measure the ultrafast spatio-temporal phase change induced by the optical Kerr effect and plasma in flexible Corning Willow Glass during femtosecond laser-matter interactions. We measure the nonlinear index of refraction ($ {n_2} $n2) to be $(3.6 \pm 0.1) \times {10^{ - 16}}\;{{\rm cm}^2}/{\rm W} $(3.6±0.1)×10-16cm2/W and visualize the plasma formation and recombination on femtosecond time scales in a single shot. To compare with the experiment, we carry out numerical simulations by solving the nonlinear envelope equation.

Femtosecond laser-matter interactions in ternary zinc phosphate glasses

We investigate the interaction of ultrashort laser pulses with ternary zinc phosphate glasses. We explore the viability of ten different glass compositions with different levels of alumina to inscribe optical waveguides via the fs-laser direct writing technique, finding that only samples with [O]/[P] ratios of 3.25 are suitable candidates. We also test a zinc magnesium phosphate glass to fabricate waveguide Bragg gratings in order to generate filters and mirrors with specific spectral properties. Confocal Raman spectroscopy inspection shows that laser-damaged material exhibits a relative intensity decrease and a subtle blue-shift on the 1209 cm-1 Raman peak, which implies a relative reduction on the content of Q(2) tetrahedra species within the glass network thus suggesting a laser-induced depolymerization. In contrast, optical waveguides and smooth laser-induced changes do not exhibit such noticeable structural modifications.

Experimental and FDTD study of silicon surface morphology induced by femtosecond laser irradiation at a high substrate temperature.

Substrate temperature is an important parameter for controlling the properties of femtosecond laser induced surface structures besides traditional ways. The morphology on silicon surface at different temperatures are studied experimentally. Compared to those formed at 300 K, smoother ripples, micro-grooves and nano/micro-holes are formed at 700 K. A two temperature model and FDTD method are used to discuss the temperature dependence of surface structures. The results show that the increased light absorption at elevated temperature leads to the reduction of surface roughness. The type-g feature in the FDTD-η map at 700 K, which corresponds to the energy deposition modulation parallel to the laser polarization with a periodicity bigger than the wavelength, is the origin of the formation of grooves. This work can benefit both surface structures based applications and the study of femtosecond laser-matter interactions.

Laser fluence dependence on emission dynamics of ultrafast laser induced copper plasma

The characteristic emission features of a laser-produced plasma depend strongly on the laser fluence. We investigated the spatial and temporal dynamics of neutrals and ions in a femtosecond laser (800 nm, ∼40 fs, Ti:Sapphire) induced copper plasma in vacuum using both optical emission spectroscopy (OES) and spectrally resolved two-dimensional (2D) imaging over a wide fluence range of 0.5–77.5 J/cm2. 2D fast gated monochromatic images showed a distinct plume splitting between the neutrals and ions, especially at moderate to higher fluence. OES studies at low to moderate laser fluence confirm intense neutral line emission over ion emission, whereas this trend changes at higher laser fluence with dominance of the latter. This evidences a clear change in the physical processes involved in the femtosecond laser-matter interaction at high input laser intensity. The obtained ion dynamics resulting from OES and spectrally resolved 2D imaging are compared with charged particle measurement employing Faraday cup and Langmuir probe; results showed good correlation.

Iron Isotope Composition of Particles Produced by UV-Femtosecond Laser Ablation of Natural Oxides, Sulfides, and Carbonates

The need for femtosecond laser ablation (fs-LA) systems coupled to MC-ICP-MS to accurately perform in situ stable isotope analyses remains an open question, because of the lack of knowledge concerning ablation-related isotopic fractionation in this regime. We report the first iron isotope analysis of size-resolved, laser-induced particles of natural magnetite, siderite, pyrrhotite, and pyrite, collected through cascade impaction, followed by analysis by solution nebulization MC-ICP-MS, as well as imaging using electron microscopy. Iron mass distributions are independent of mineralogy, and particle morphology includes both spheres and agglomerates for all ablated phases. X-ray spectroscopy shows elemental fractionation in siderite (C-rich agglomerates) and pyrrhotite/pyrite (S-rich spheres). We find an increase in (56)Fe/(54)Fe ratios of +2‰, +1.2‰, and +0.8‰ with increasing particle size for magnetite, siderite, and pyrrhotite, respectively. Fe isotope differences in size-sorted aerosols from pyrite ablation are not analytically resolvable. Experimental data are discussed using models of particles generation by Hergenröder and elemental/isotopic fractionation by Richter. We interpret the isotopic fractionation to be related to the iron condensation time scale, dependent on its saturation in the gas phase, as a function of mineral composition. Despite the isotopic variations across aerosol size fractions, total aerosol composition, as calculated from mass balance, confirms that fs-LA produces a stoichiometric sampling in terms of isotopic composition. Specifically, both elemental and isotopic fractionation are produced by particle generation processes and not by femtosecond laser-matter interactions. These results provide critical insights into the analytical requirements for laser-ablation-based stable isotope measurements of high-precision and accuracy in geological samples, including the importance of quantitative aerosol transport to the ICP.

Examination of femtosecond laser matter interaction in multipulse regime for surface nanopatterning of vitreous substrates

The paper presents our results on laser micro- and nanostructuring of sodium aluminosilicate glass for the permanent storage purposes and photonics applications. Surface structuring is realized by fs laser irradiation followed by the subsequent etching in a potassium hydroxide (10M@80 °C) for 1 to 10 minutes. As the energy deposited is lower than the damage and/or ablation threshold, the chemical etching permits to produce small craters in the laser modified region. The laser parameters dependent interaction regimes are revealed by microscopic analysis (SEM and AFM). The influence of etching time on craters formation is investigated under different incident energies, number of pulses and polarization states.

Preliminary evidences of AC-run-away in femtosecond laser-matter interaction

The role of collisional absorption is shown to be important at the beginning of the interaction between a laser pulse and matter, i.e., a plasma, while later on collective absorption phenomena take place. The scope of this paper is to present first results about the long predicted AC-run-away effect, defined as a sudden transition from a collisional absorption regime to a collective one, in ideal circumstances: for an ultrashort laser pulse, i.e., subpicosecond pulses, and with a sharp plasma boundary, i.e., without a laser prepulse. For this purpose, we use a kinetic model based on the ballistic theory. The model is of relevance to laser-matter interaction including laser nuclear fusion or laser particle acceleration.

Spectral and temporal characteristics of metallic nanoparticles produced by femtosecond laser pulses

We study the time of flight optical emission from titanium and tungsten nanosized particles, generated through femtosecond laser-matter interaction in vacuum, in the wavelength spectral range from 300 to 900 nm. Typical spectra consist of broadband structureless signals similar to black body emission from a macroscopic object. Nanoparticles temperature, deduced from their emission spectra, decreases drastically as a function of their time of arrival at a given distance from the target. This behaviour is seen to be independent of individual particle velocities.

Characterization of preformed plasmas with an interferometer for ultra-short high-intensity laser-plasma interactions

The evolution of an Al preformed plasma produced by a prepulse was observed before and after the arrival of the main pulse by an interferometer using a femtosecond probe pulse. A central density depression due to the ponderomotive force of the main laser pulse in the preformed plasma with a ∼100 μm scale length was clearly visible after the main pulse irradiation at an intensity of ∼5×1016 W/cm2. The temporal profiles of the prepulse, characterized by a cross-correlation in conjunction with a precise density profile measurement by an interferometer, contribute to the better understanding of femtosecond laser-matter interactions.

Comparison of heat-affected zones due to nanosecond and femtosecond laser pulses using transmission electronic microscopy

This letter presents a method aimed at quantifying the dimensions of the heat-affected zone (HAZ), produced during nanosecond and femtosecond laser–matter interactions. According to this method, 0.1 μm thick Al samples were microdrilled and observed by a transmission electronic microscopy technique. The holes were produced at laser fluences above the ablation threshold in both nanosecond and femtosecond regimes (i.e., 5 and 2 J/cm2, respectively). The grain size in the samples was observed near the microholes. The main conclusion is that a 40 μm wide HAZ is induced by the nanosecond pulses, whereas the femtosecond regime does not produce any observable HAZ. It turns out that the width of the femtosecond HAZ is less than 2 μm, which is our observation limit.

A novel method for detection of strong magnetic fields in femtosecond laser–matter interaction

Femtosecond laser–matter interaction can produce strongly magnetized dense plasmas via ultrafast ionization process. This paper proposes a diagnostic—which is not yet existing as far as we know—to prove the existence and to measure the strength of the quasistatic magnetic field in overdense plasma where the Faraday rotation method is not applicable. The method is based on the analysis of the propagation of a quasi-longitudinal right circular polarized electromagnetic probe wave, i.e., a whistler wave. The method is applicable when the quasistatic magnetic field is strong enough (some tens of megagauss) and the overdense plasma electron density not too high (ne⩽5×1022 cm−3).

First applications of the ballistic model in femtosecond laser–matter interaction: Preliminary evidence of ac-run-away and new features about normal skin effect

The role of collisional absorption is supposed to be important in the beginning of the interaction between a laser pulse and matter. Later on, collective absorption phenomenons take place. The scope of this paper is to present first results about the so-called AC-run-away effect, defined as a “sudden transition from collisional absorption regime to a collective one.” For this purpose, we use a simple model based on ballistic theory. The delicate point concerning the Coulomb logarithm is also studied: we propose for it a convenient cutoff and an ensemble averaged Coulomb logarithm fit formula. Another application of the model presented here is the normal skin effect. We show some sensible differences between the present approach and those based on more common and rough collision frequency formulas.