Alika Khare

Size induced structural modifications in copper oxide nanoparticles synthesized via laser ablation in liquids

Laser induced breakdown at copper-water interface is employed to synthesize copper oxide nanoparticles. Copper forms two stable oxides: monoclinic CuO and cubic Cu2O. The characteristic traits of laser induced plasma at copper-water interface are altered to analyze the size induced structural modifications in these oxides. The properties of laser produced plasma were varied by changing the focusing conditions of the source laser. Tightly focused condition led to formation of CuO of size ≤ 200 nm whereas laser defocusing condition produces nanocolloids of Cu2O of size less than 10 nm. These findings were attributed to high pressure (60 GPa) accompanied by high temperature at tightly focused condition which results in growth of covalent CuO whereas lower pressure (1.3 GPa) and low temperature at defocused condition probably forms symmetric Cu2O.

Effect of focusing conditions on laser-induced shock waves at titanium–water interface

The spatial and temporal evolution of laser-induced shock waves at a titanium-water interface was analyzed using a beam deflection setup. The focusing conditions of the source laser were varied, and its effect onto the dynamics of shock waves was elucidated. For a tightly focused condition, the speed of the shock wave was ~6.4 Km/s, whereas for a defocused condition the velocities reduced to <3 km/s at the vicinity of the titanium-water interface. When the laser is focused a few millimeters above the target, i.e., within the water, the emission of dual shock waves was observed toward the rear side of the focal volume. These shock waves originate from the titanium-water interface as well as from the pure water breakdown region, respectively. The shock wave pressure is estimated from the shock wave velocity using the Newtons second law across a shock wave discontinuity. The shock wave pressure for a tightly focused condition was 18 GPa, whereas under a defocused condition the pressure experienced was ≤1 GPa in the proximity of target.

Mirrorlike pulsed laser deposited tungsten thin film

Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ∼782 nm.

Spectroscopic studies of laser ablated ZnO plasma and correlation with pulsed laser deposited ZnO thin film properties

In this paper, measurement of various plasma parameters during pulsed laser deposition of ZnO thin films on Si (100) substrates is reported. The variations of electron number density and electron temperature with ambient pressure and target substrate distance is obtained via spectroscopic measurements. The structural and optical properties of ZnO thin films were analyzed using X-ray diffraction, scanning electron microscope, and photoluminescence and then correlated with spectroscopic results to find optimum conditions for the deposition of high quality ZnO thin films.

Molybdenum thin films via pulsed laser deposition technique for first mirror application

Mirror like Molybdenum thin films on SS substrate in vacuum (10 −3 Pa) and in Helium environment has been achieved by Pulsed Laser Deposition (PLD) Technique. The PLD thin films of Molybdenum have been characterized by using X-ray Diffraction (XRD) pattern, Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Energy Dispersive X-ray (EDX). The specular reflectivity was recorded with Fourier Transform Infra-Red spectrometer and UV-Visible spectrometer. The optical quality of the thin films was tested via interferometric technique. At the optimum deposition parameters, the crystal orientation was in Mo(110) phase. The FIR-UV-Visible reflectivity of the mirror was found to be closed to that of the polished bulk Molybdenum and Stainless Substrate (SS) substrate.

Structural and linear and nonlinear optical properties of Zn 1-x Al x O (0≤x≤0.10) thin films fabricated via pulsed laser deposition technique

The effect of Al doping on linear and nonlinear optical properties of pulsed laser deposited (PLD) Zn1-xAlxO (AZO) thin films is reported. The increase in 002 peak in X-ray diffraction pattern up to x = 0.05 is indicative of improvement in the wurtzite phase and was also confirmed by enhancement in E2 (high) peak at 438 cm−1 of Raman spectra. The increase in the blue shift in the band gap up to x = 0.05 suggests the Burstein Moss effect. The red shift in the band gap for x>0.05 can be interpreted due to the band gap renormalization as a result of many body interaction effects. The two photon absorption coefficients (β) and nonlinear refractive indices (n2) measured via z-scan measurement were found to be in the range of 3.4-8.0 cm/W and (1.0-5.2) × 10−4 cm2/W for x = 0.00-0.10 respectively. An attempt is made to correlate the linear and nonlinear optical behavior and crystal structure as a function of level of Aluminum doping (x).

Synthesis of TiO2 Nanoparticles Via Laser Ablation at Titanium-Water Interface

Pulsed laser induced breakdown at target-water interface is used to synthesize TiO2 nanoparticles. Ablation at defocused and tightly focused condition resulted in TiO2 nanoparticles in anatase and rutile phase respectively. In addition, insufficiently oxidized Ti2O3 nanoparticles are also observed due to transient quenching during laser induced breakdown process. The TiO2 nanoparticle phase and sizes are diagnosed using TEM. The optical properties are characterized using Raman and UV-Vis spectra. The estimated optical band gap from the absorption spectra of TiO2 anatase phase is 3.23 eV and of TiO2 rutile phase is 3.0 eV.

Measurement of charged particles and cavitation bubble expansion velocities in laser induced breakdown in water

The measurement of charged particles and cavitation bubble expansion velocity is reported in a laser induced breakdown in water using beam deflection set-up. Effect of laser power on charged particles, cavitation bubble velocities and higher order bubble oscillations is also studied.

Sculpted pulsed indium atomic beams via selective laser ablation of thin film

We present a novel experiment for the generation of sculpted pulsed indium atomic beams of regular arrays in one and two-dimensions via rear side ablation of indium by two and four beams interference pattern using second harmonic of high power Nd: YAG laser under high vacuum (10 −5 Torr).

Effect of target–substrate distance onto the nanostructured rhodium thin films via PLD technique

Rhodium thin films on highly polished stainless steel substrates were fabricated via pulsed laser deposition (PLD) technique. The PLD films of rhodium were observed to be preferentially oriented in Rh(111) plane. The films showed dense columnar structure of nanometric crystallites. The effects of target–substrate distance onto the root mean square roughness, crystal structure, reflectivity and thickness of the PLD rhodium films were investigated.