Arpita Nath

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.

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.

Seventh-harmonic generation from tightly focused 2 μm ultrashort pulses in air.

We report generation of third, fifth and seventh harmonics from air by using tightly focused, ultrashort pulses of short-wave infrared (2 μm) radiation. We have measured the third- and fifth-harmonic efficiencies to be 5×10(-5) and ~1.4×10(-5), respectively, with the ratio of fifth-to-third-harmonic efficiency being close to 0.28. Our experimental results provide confirmation of expectations of the higher-order Kerr effect model.

Laser-induced high-pressure and high-temperature conditions at the titanium–water interface and their implication on TiO 2 nanoparticles

Pulsed laser-induced breakdown at the titanium–water interface leads to the formation of titanium–water plasma, which evokes high-pressure and high-temperature (HPHT) conditions at the interfacial region and under suitable condition results in the formation of TiO2 nanoparticles. Laser-induced HPHT conditions at the titanium–water interface are characterized using the beam deflection setup and laser-induced breakdown spectroscopy, respectively. An estimate of HPHT at the interface is used to gain insight into the nucleation process of TiO2 nanoparticles. Assuming the existence of the thermodynamical equilibrium between the titanium and water plasma, the pressure and temperature at the interface are employed to measure the nucleation time, growth velocity, and the size of the nanoparticles for comparison with the synthesized nanoparticles.

Spectroscopic investigations on laser induced breakdown in water

The band spectrum of molecular and radical species generated via laser induced breakdown in water is reported. The dependence of band spectra of various species on to the different regions of plasma is analyzed.

Antimicrobial and micro Raman spectroscopy of selected Zingiberaceae species from Northeast India

Antimicrobial activity of crude rhizome oils from some important members of Zingiberaceae from Northeast India was carried out in the present study. The plants used were Curcuma amada, C. longa, Zingiber moran, and Z. zerumbet. Rhizomes of the four species were collected and rhizome oil was extracted using six different polar and non-polar solvents. The antimicrobial property of the crude oil was studied against human pathogens using disc-diffusion and viability assay. The rhizome oil of all the 24 extracts exhibited potent antimicrobial activity against all pathogenic bacterial and fungal strains tested. Hydrodistilled fractions of the four species studied showed better effect among all solvents. Water extract of Z. moran was found to be the highest effective antimicrobial agent of all. Antibacterial effect of the water fractions was also characterized against Gram-positive and Gram-negative bacteria using micro Raman spectroscopy. This investigation shows that the essential oils from the wild and domestic species of the family Zingiberaceae from Northeast India are a potential source of bioactive compounds with tremendous medicinal, economic, and therapeutic value. The wild and endemic species Z. moran represents an interesting and promising source of plant-derived antimicrobial agent in the development of new drugs against pathogens.

Antibacterial activity of Cu@Cu2O nanoparticles synthesized via laser ablation in liquids

Laser induced breakdown at copper-water interface was used to synthesize Copper@CopperOxide nanocomposites in the colloidal form. The antibacterial activities of these nanoparticles were studied using UV-Vis and Raman spectroscopy.