A. Latif

Laser Irradiation Effects on Gold

Investigations on the laser irradiation effects on gold are explored in terms of plasma-plume dynamics and morphological and crystallographic changes. Annealed 4N gold samples were irradiated with a Q-switched Nd:YAG laser (53 mJ, 21 MW, 532 nm, and pulse width 6–8 ns) for plume dynamics using 10-ns gated fast photography. A Q-switched pulsed Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns) was used to irradiate the surface of the samples for morphological and crystallographic studies of laser-irradiated gold in a vacuum ∼10−3 Torr. The annealed samples were exposed to 50 shots of a Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns). The investigation on the plume was done by using an intensified charged-couple device ICCD-5760/IR-UV camera. The morphological investigation of the irradiated surface was carried out by analyzing micrographs obtained using an Hitachi S 3000 H scanning-electron microscope (SEM). The crystallographic studies of the irradiated samples were performed by analyzing the XRD patterns obtained using an X’ Pert Pro Pan Analytical X-ray diffractometer. The investigation on gated ICCD images of the plume reveal that, at very earlier times, the plasma-plume expansion has a linear trend, whereas, at later times, the plasma-plume expansion is nonuniform. SEM micrographs exhibit the primary mechanisms of pulsed-laser ablation (PLA), such as hydrodynamic sputtering, thermal sputtering, exfoliation sputtering, and splashing. The surface morphology was explained in terms of crater formation, swelling, burning, nucleation, grain growth, and nonsymmetric heat conduction. The nonuniform thermal expansion of gold due to thermal-energy transfer is also studied by SEM micrographs, which was supported by XRD analysis. The structural analysis on the basis of XRD shows that the composition of the irradiated samples is not disturbed even after laser irradiation. The grain sizes also changed due to laser irradiation.

Theoretical model for heat conduction in metals during interaction with ultra short laser pulse

Theoretical studies have been performed on the interaction of short laser pulse with metals. The results of the theoretical model indicate that heat conduction would not be uniform from focal spot or crater at the surface of target metal, when an ultra short laser will interact with the metal. The electromagnetic radiations of laser induce electric field inside the target that is responsible for the induction of current density, which causes electronic heat conduction in the direction of current density. Such an effect is dominant for laser pulse having duration less than of the order of sub-picoseconds. This mode will open a new significant field of study to discuss laser metal interaction for ultra short laser pulses.

Irradiation effects on copper

Copper, one of the most significant metals, is exposed to IR radiation. A Nd:YAG laser (1064 nm, 1.1 MW, 12 ns) has been used to irradiate fine polished and annealed samples (4 N, 1×1×0.3 cm3) with 100 laser shots under a vacuum of ∼10−6 torr. The laser focal spot size and power density on the target were 12 μm and 3×1012 Wm−2 respectively. The surface and structural studies were performed by analyzing scanning electron micrographs and X-ray diffractograms (XRDs), respectively. Laser ablation results in boiling, splashing, hydrodynamical sputtering and exfoliation along with other relevant phenomena. The XRD patterns of the exposed sample indicate a change in diffraction intensity and grain sizes. The atomic planes remain undisturbed for the irradiated target. The information collected is useful for investigating the complexities found in radiation–metal interactions.

Surface modifications of materials by repetitive laser pulses

Laser-induced modifications on platinum (Pt) and silicon (Si) are compared by considering the development of various features on the irradiated surface. The experiments were carried out both in air and under vacuum. The interaction of 50 pulses of 1064 nm Nd:YAG laser with both targets in air resulted in non-linear phenomena. The periphery of the irradiated spot on the Pt surface exhibits wave-like patterns with a featureless central portion. A non-uniform distribution of cones of different sizes is also observed on the irradiated surface. In the case of silicon, the laser-induced periodic surface structures along with the formation of micro-column, rectangular blocks and grid are prominently observed features. However, when both the targets were irradiated with the same number of shots under vacuum (∼10−3 Torr), the surface morphologies of both the targets exhibited the hydrodynamic sputtering but with more explosive expulsion in Pt when compared with silicon. In platinum, there is a periodic variation in the distance between adjacent cones formed in various ablated zones. The Gaussian beam mode TEM00 provided the evidences for melt pool formation in silicon when irradiated under vacuum. Additionally, we observed other mechanisms including splashing, sputtering, burning, re-solidification and redeposition on the surface of irradiated targets.

Crystallography and surface morphology of ion-irradiated silver

Investigations are performed to explore the surface morphological and crystallographic changes induced by the irradiation of laser-produced copper ions on 4N pure polished silver samples under vacuum (∼10−3 torr). The morphology was changed a great deal, with prominence in sputtering, hill and crater formation. Variation in grain size, dislocation line density and strain are the major observed crystallographic changes.

Laser shots impact on geometry of crater evolution at copper surface

Fine polished 4N (99.99%) pure copper samples are irradiated in ambient air using Q-Switched Nd:YAG Laser (10 mJ, 9–12 ns, 1064 nm). The laser energy density and spot size at tight focus are 3×1011 W/cm2 and ∼12 μm, respectively. The laser-produced crater is analyzed considering its dimensional changes with the increase in laser shots employing optical microscopy. The width of the crater (along horizontal) increases, thereby exhibiting its exponential trend. The length along the vertical and the depth of the crater both increase exponentially. The heat-affected zone expands exponentially as well. Hydrodynamics and exfoliation are the two main dominant observed ablation mechanisms.

Effect of UV irradiation on the structural, optical and electrical properties of platinum

Investigations are performed on thermal, optical and electrical response of UV laser-irradiated platinum (Pt). 4N pure, annealed and fine polished samples are exposed to the KrF Excimer laser (248 nm, 20 ns, 50 mJ) under vacuum ∼10−6 torr at different laser fluences (0.5–2.5 J/cm2). Space-resolved plasma plume dynamics is studied by analyzing the captured plume images with the help of a computer controlled image-grabbing system. The irradiated targets are characterized for surface morphology, structural, optical and electrical investigations using the diagnostics; scanning electron microscopy, X-ray diffraction, rotating compensator auto-aligned ellipsometer and four-point probe, respectively. The value of maximum intensity emitted by Pt plasma plume is 250 grey scales. Surfaces of the target metals are modified by craters, moltens and redeposited material. Laser-induced periodic surface structures are produced at low laser fluence. Irradiation of Pt causes changes in diffracted X-rays intensity and grain sizes, dislocation in line densities and strain in the target materials. Considerable changes occur in optical parameters as well. A decrease in electrical conductivity of the irradiated targets also takes place in an exponential way with the change in laser fluence.

Comparison of the laser-induced plasma of different metal targets as X-rays sources in vacuum

ABSTRACT Laser-induced plasma is a good source of X-rays. It has much importance in different fields such as industry and medical field. In the current work, Nd: YAG laser was irradiated on metal targets (Al, Cu, Ni, Zn, Sb and Pb) under vacuum 10−3 torr. Plasma plume is captured by the charged couple device. The emitted X-rays from plasma plume are detected by BPX-65 PIN photodiode through a proper biasing circuit and electrical signals are stored by digital storage oscilloscope (UNI-T UT2202C, 200 MHz). Energy was calculated from these electrical signals. The parameters of X-rays are strongly dependent on the atomic number.

Surface and structural investigations on laser irradiated P-type silicon

P-type silicon (100) is irradiated with Nd:YAG laser (532 nm, 500 mJ and 6–7 ns) in air at room temperature for two different laser incident angles 0° and 45° with the surface normal of the target for 10–50 laser shots with a step of 10 shots. The surface morphological changes of exposed samples are explored by making use of the scanning electron microscope. The variations in crystal structure and crystallinity along with laser annealing effects are examined by employing Raman spectroscopy. The thermal sputtering, hydrodynamic sputtering, exfoliation sputtering, whisker formation and bubble bursting are the salient features found on the irradiated surfaces. An increase in laser shots causes incremental changes in area of melted and heat-affected zones and Raman shifts.