Interaction of Long Time Pulses of an Nd3+:YAG Laser Beam with the Heusler AlloyNi45Co5Mn35.5In14.5

In this paper, the laser processing of the surface of bulk and layered samples (of thickness 75 nm) of Ni45Co5Mn35.5In14.5 alloy (NC5MI) was investigated using microsecond laser pulses. A Q-switched pulsed Nd3+:YAG laser, operating in the 1st harmonic (which had a wavelength of 1064 nm) with a pulse duration of 250 µs, was used. NC5MI is a metal resistant to thermal laser processing because its reflection coefficient is close to unity for long wavelengths. The aim of this paper was to learn the forms of laser processing (heating, microprocessing, ablation) for which the above-specified type of laser is useful. The samples were irradiated with various fluences in the interval of 5–32 J·cm−2. The effect of the laser interaction with the surface was explored by SEM microscopy. The threshold fluences for the bulk sample were determined as: the visible damage threshold (Fthd = 2 ± 0.2 J·cm−2), the melting threshold (Fthm = 10 ± 0.5 J·cm−2), and the deep melting threshold (Fthdm = 32 J·cm−2). Unexpectedly, these values wereincreased for the layer sample due to its silicon substrate. We have concluded that this type of laser radiation is advantageous for the annealing and melting of, or drilling holes in, the alloy, but disadvantageousto the ablation of the alloy.

Computer simulation of temperature fields in the Cr (film)-Zr (substrate) system during pulsed electron-beam irradiation

The paper presents the results of numerical simulation of the distribution of thermal fields during the formation of Cr-Zr surface alloy using a pulsed low-energy high-current electron beam (LEHCEB). The melting thresholds of the Cr-Zr system for different thicknesses of Cr films were calculated. The melting threshold of the Cr-Zr system increases linearly with increasing Cr film thickness. A linear regression dependency model of the melting threshold on the film thickness is proposed. Evaporation thresholds of the Cr-Zr system for different thicknesses of Cr films were calculated. The evaporation threshold of the Cr-Zr system increases linearly with increasing Cr film thickness. A linear regression dependency model of the evaporation threshold on the film thickness is proposed. The value of the LEHCEB energy density at which the lifetime of the film and substrate are equal is calculated. This value is a maximum value for the effective formation of Cr-Zr. A model of the LEHCEB energy density, at which the lifetime of the film and the substrate are equal, in the form of a third-degree polynomial is proposed.

MODIFICATION AND ALLOYING EFFECTS IN EUROFER STEEL UNDER POWERFUL PULSED PLASMA IMPACTS

Experimental studies of surface modification of Eurofer samples have been performed with a quasi-stationary plasma accelerator QSPA Kh-50. The heat load on the surface was near the tungsten melting threshold (i.e. about 0.6 MJ/m2). The plasma streams exposures result in modification of steel-based materials and formation of cellular submicron structures in re-solidified layers. Phase characterized by body-centered cubic lattice appeared due to recrystallization of affected material.

Real-space observation of surface structuring induced by ultra-fast-laser illumination far below the melting threshold

Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target. Despite extensive studies on the interaction of femto-second laser interaction with matter, the initial steps of the morphological changes are not yet fully understood. Here, we reveal that substantial surface structure changes occur at energy densities far below the melting threshold. By using low-temperature scanning tunneling microscopy we resolve atomic-scale changes, i.e. the creation of nanosized adatom and vacancy clusters. The two cluster types have distinct non-linear fluence-dependencies. A theoretical analysis reveals their creation and motion to be non-thermal in nature. The formation of these atomistic changes, individually resolved here for the first time, recast our understanding of how surfaces respond to low-intensity ultra-short laser illumination. A visualization and control of the initial morphological changes upon laser illumination are not only of fundamental interest, but pave the way for the designing material properties through surface structuring.

Импульсное лазерное облучение светоизлучающих структур на основе GaAs

The effects of KrF excimer laser pulses on the crystalline and optical properties of structures with four InxGa1−xAs/GaAs quantum wells (x ranged from 0.08 to 0.25) were studied. The results obtained by Raman spectroscopy and reflection spectroscopy showed that the high crystalline quality of the GaAs cap layer is retained after exposure to laser radiation with an energy density of 200 to 360 mJ/cm2. It was established experimentally by photoluminescence spectroscopy and by modeling the laser annealing process, which is a solution to the problem of heat propagation in a one-dimensional GaAs-based system, that the thermal effects that occur in heterostructures under pulsed laser irradiation below the GaAs melting threshold lead to relaxation of mechanical stresses. At the initial stages of this process, the point defects appear in InxGa1−xAs/GaAs quantum wells. The latter lead to a “red” shift of the photoluminescence emission peaks of quantum wells and serve as centers of nonradiative recombination, which causes the quenching of the photoluminescence.