Laser ablation; Micro structuring; Crater depth; Molybdenum; LIBS; Electron temperature and number density;ABLATED PLASMA EMISSION; NDYAG LASER; THIN-FILMS; METALS; ATMOSPHERE; BEAM; VAPORIZATION; PARAMETERS; FLUENCES; VACUUM

Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm(2) under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. LaserInduced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 x 10(18) to 0.72 x 10(18) cm(-3) respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm(2) followed by a decrease from 19 to 25 GW/cm(2) and then a saturation from 25 to 50 GW/cm(2). The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters.

Silicon; Laser-induced breakdown spectroscopy; Emission spectroscopy; Surface morphology; Periodic surface structures;PLASMA PARAMETERS; SURFACE-MORPHOLOGY; SILICON; ZINC; ALLOY; TEMPERATURE; DIAGNOSTICS; SPECTRA; DENSITY; GAS

The effect of nature and pressure of ambient environment on laser-induced breakdown spectroscopy (LIBS) and ablation mechanisms of silicon (Si) have been investigated. A Q-switched Nd-YAG laser with the wavelength of 1064 nm, pulse duration of 10 ns, and pulsed energy of 50 mJ was employed. Si targets were exposed under ambient environments of inert gases of argon, neon, and helium for different pressures ranging from 5 to 760 torr. The influence of nature and pressure of ambient gases on the emission intensity of Si plasma have been explored by using the LIBS spectrometer system. The plasma parameters such as electron temperature and number density were determined by applying Boltzmann plot and Stark broadening method, respectively. Our experimental results suggest that the nature and pressure of ambient environment play a significant role for generation, recombination, and expansion of plasma and consequently affect the excitation temperature as well as electron density of plasma. The surface morphological analysis of laser-irradiated Si was performed by using scanning electron microscope (SEM). Various kinds of structures, for example laser-induced periodic surface structures or ripples, cones, droplets, and craters have been generated and their density and size are found to be strongly dependent upon the ambient environment. A quantitative analysis of particulate size and crater depth measured from SEM images showed a strong correlation between plasma parameters and the growth of micro/nanostructures on the modified Si surface.

INDUCED BREAKDOWN SPECTROSCOPY; EMISSION-SPECTROSCOPY; ABLATION; ENHANCEMENT; TITANIUM; ALUMINUM; METALS

The role of spatial confinement for improvement of laser-induced Mg plasma parameters and growth of surface features is investigated by introducing a metallic blocker. Nd: YAG laser at various fluences ranging from 7 to 28 J cm(-2) was employed as an irradiation source. All measurements were performed in the presence of Ar under different pressures. Confinement effects offered by metallic blocker are investigated by placing the blocker at different distances of 6, 8 and 10 mm from the target surface. It is revealed from laser-induced breakdown spectroscopy analysis that both plasma parameters, i.e., excitation temperature and electron number density initially increase with increasing laser fluence due to enhancement in energy deposition. With further increase in laser fluence, a decreasing trend followed by saturation is observed which is attributable to shielding effect and self-regulating regime. It is also observed that spatial confinement offered by metallic blocker is responsible for the significant enhancement of both electron temperature and electron number density of Mg plasma. This is true for all laser fluences and pressures of Ar. Maximum values of electron temperature and electron number density without blocker are 8335 K and 2.4 x 10(16) cm(-3), respectively, whereas these values are enhanced to 12,200 K and 4 x 10(16) cm(-3) in the presence of the blocker. The physical mechanisms responsible for the enhancement of Mg plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning electron microscope analysis was performed to explore the surface morphology of laser-ablated Mg. It reveals the formation of cones, cavities and ripples. These features become more distinct and well defined in the presence of the blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

Electron number density; Electron temperature; Laser-induced breakdown spectroscopy; Spatial confinement; Spectral emissions;PLASMA; TEMPERATURE; ABLATION; DENSITY

Spatial confinement effects on plasma parameters and surface morphology of laser-ablated Mg are studied by introducing a metallic blocker as well as argon (Ar) gas at different pressures. Nd: YAG laser at various fluences ranging from 7 to 28 J/cm(2) was employed to generate Mg plasma. Confinement effects offered by metallic blocker are investigated by placing the blocker at different distances of 6, 8, and 10 mm from the target surface; whereas spatial confinement offered by environmental gas is explored under four different pressures of 5, 10, 20, and 50 Torr. Laser-induced breakdown spectroscopy analysis revealed that both plasma parameters, that is, excitation temperature and electron number density initially are strongly dependent upon both pressures of environmental gases and distances of blockers. The maximum electron temperature of Mg plasma is achieved at Ar gas pressure of 20 Torr, whereas maximum electron number density is achieved at 50 Torr. It is also observed that spatial confinement offered by metallic blocker is responsible for the significant enhancement of both electron temperature and electron number density of Mg plasma. Maximum values of electron temperature and electron number density without blocker are 8335 K and 2.4 x 10(16) cm(-3), respectively, whereas these values are enhanced to 12,200 K and 4 x 10(16) cm(-3) in the presence of blocker. Physical mechanisms responsible for the enhancement of Mg plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning electron microscope analysis was performed to explore the surface morphology of laser-ablated Mg. It reveals the formation of ripples and channels that become more distinct in the presence of blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

Laser-induced breakdown spectroscopy; Electron temperature; Number density; Magnetic confinement; Surface structuring;X-RAY-EMISSION; OPTICAL-EMISSION; ELECTRON-DENSITY; CARBON PLASMA; AMBIENT GAS; ABLATION; PLUME; TEMPERATURE; CONFINEMENT; PARAMETERS

The effect of the transverse magnetic field on laser-induced breakdown spectroscopy and surface modifications of germanium (Ge) has been investigated at various fluences. Ge targets were exposed to Nd: YAG laser pulses (1064 nm, 10 ns, 1 Hz) at different fluences ranging from 3 to 25.6 J/cm(2) to generate Ge plasma under argon environment at a pressure of 50 Torr. The magnetic field of strength 0.45 Tesla perpendicular to the direction of plasma expansion was employed by using two permanent magnets. The emission spectra of laser-induced Ge plasma was detected by the laser-induced breakdown spectroscopysystem. The electron temperature and number density of Ge plasma are evaluated by using the Boltzmann plot and stark broadening methods, respectively. The variations in emission intensity, electron temperature (T-e), and number density (n(e)) of Germanium plasma are explored at various fluences, with and without employment of the magnetic field. It is observed that the magnetic field is responsible for significant enhancement of both excitation temperature and number density at all fluences. It is revealed that an excitation temperature increases from T-e,T-max,T-without B = 16,190 to T-e,T-max,T-with B = 20,123 K. Similarly, the two times enhancement in the electron density is observed from n(e,max,without B) = 2 x 10(18) to n(e,max,with B) = 4 x 10(18) cm(-3). The overall enhancement in Ge plasma parameters in the presence of the magnetic field is attributed to the Joule heating effect and adiabatic compression. With increasing fluence both plasma parameters increase and achieve their maxima at a fluence of 12.8 J/cm(2) and then decrease. In order to correlate the plasma parameters with surface modification, scanning electron microscope analysis of irradiated Ge was performed. Droplets and cones are formed for both cases. However, the growth of ridges and distinctness of features is more pronounced in case of the absence of the magnetic field; whereas surface structures become more diffusive in the presence of the magnetic field.

Laser induced breakdown spectroscopy; Magnetic field confinement; Emission intensity; Electron temperature; Electron density; ZrO2 plume;X-RAY-EMISSION; OPTICAL-EMISSION; ALUMINUM PLASMA; MASS REMOVAL; ENHANCEMENT; PLUME; DIAGNOSTICS; SATURATION; DEPOSITION; ABLATION

Laser induced breakdown spectroscopy of ZrO2 plasma in the presence and absence of magnetic field has been investigated. The plasma was generated by employing Nd:YAG laser (1064 nm, 10 ns) at various fluences ranging from 6.4J cm(-2) to 25.6J cm(-2) under argon environment of pressure of 100 Torr. Both emission intensity and electron temperature show increasing trend with increasing the fluence, whereas, electron number density of ZrO2 plasma decreases with increasing the laser fluence. It is revealed that values of emission intensity, electron temperature and electron number density of ZrO2 plasma are slightly higher in the presence of magnetic field as compared to field free case at all fluences. This increase in plasma parameters is attributed to magnetic confinement and Joule heating effect. With the variation of fluence the electron temperature of ZrO2 plasma varies slightly from 5345 K to 5475 K in the absence of magnetic field, whereas in case of magnetic field this value enhances from 5435 K to 5600 K. Similarly the electron number density of ZrO2 plasma varies from 1.80 x 10(18) cm(-3) to 3.50 x 10(18) cm(-3) in the absence of magnetic field, whereas in case of magnetic field, the variation in electron number density varies from 1.75 x 10(18) cm(-3) to 4.25 x 10(18) cm(-3). The existence of magnetic confinement effects is confirmed by the analytical evaluation of plasma parameter beta, which is smaller than 1 under all experimental conditions. It is also revealed that both the laser fluence as well as magnetic field significantly influence the ZrO2 plasma parameters. (C) 2017 Elsevier GmbH. All rights reserved.