Alika Khare

The deposition of energy-harvesting Mn₂O₃ onto the “Cu” electrode is reported using pulsed laser ablation at the manganese–water interface. Conventionally, laser-induced plasma deposition is carried out by orthogonally placing the substrate (electrodes) in the plasma expansion. Here, underwater material deposition is observed on electrodes placed parallel to the plasma expansion. The possible role played by the fluid dynamically assisted microbubbles in transporting the materials onto electrodes is investigated here. To verify the influence of microbubbles, external electric fields are employed, and implications for the electrodes are characterized. The studies reveal that the external field intensifies the flow of the microbubbles towards the walls, which assists in the deposition of Mn₂O₃ on the electrodes.

In this paper we propose a zonal wavefront sensing scheme that facilitates wavefront measurement with enhanced sensitivity at the standard video rate. We achieve this enhanced sensitivity by implementing a sequential display of binary holograms described over each zone sampling the incident wavefront with the help of a ferroelectric liquid crystal spatial light modulator. By keeping the number of active zones as 24 and using a camera with an imaging frame rate equal to the binary hologram display rate of the spatial light modulator, we are able to reach a sensing frame rate of 60 Hz. In addition to enhanced sensitivity, the proposed scheme facilitates zone-wise tuning of binary holograms and eliminates the possibility of any crosstalk between adjacent zones. We perform a proof-of-principle experiment that validates the proposed zonal wavefront sensing scheme and demonstrates its advantages.

Herein, we report the plasmonic upconversion (UC) emission enhancement of Gd₂O₃:Er³⁺/Yb³⁺ thin films grown on randomly distributed gold nanoparticles (AuNPs) on glass. The AuNPs were prepared by thermal annealing a gold thin film on a glass substrate at 500 °C for 2 h. Gd₂O₃:Er³⁺/Yb³⁺ thin films were deposited on AuNPs using the pulsed laser deposition technique. The prepared plasmonic films exhibited stronger UC emission intensities in comparison to the reference Gd₂O₃:Er³⁺/Yb³⁺ thin film. This enhancement in UC intensity was assumed to be due to the strong optical field associated with the localized surface plasmon resonance (LSPR) and strong light scattering from AuNPs. A theoretical simulation based on a finite element method was performed to understand the nature of the optical field confined in AuNPs present in the Gd₂O₃:Er³⁺/Yb³⁺ thin film. This study is believed to be beneficial for several applications such as thin film-based infrared detectors and high efficiency photovoltaic devices.

In this manuscript, the time-resolved laser-induced breakdown spectroscopy (LIBS) on tungsten target in air and the coexistence of LTE among atoms and ions as well as the fulfillment of optically thin plasma condition are reported. The laser-induced plasma (LIP) of tungsten is generated by focusing the second harmonic of a Q-switched Nd:YAG laser of pulse width ~7 ns and repetition rate of 1 Hz on the tungsten target. The temporal evolution of LIP of tungsten is recorded at four different incident laser fluences of 60, 120, 180, and 270 J/cm². The several atomic and singly ionized lines of tungsten are identified in LIP. For the estimation of plasma temperature via the Boltzmann plot, the transitions at 430.7, 449.4, 468.0, 484.3, 505.3, and 524.2 nm of Atomic transition of tungsten (WI) and that of the ionic transitions, First Ionic transition of Tungsten (WII) at 251.0, 272.9, and 357.2 nm are selected. The electron density is estimated using the Stark-broadened profile of WI line at 430.2 nm. The McWhirter criteria for the local thermodynamic equilibrium (LTE) condition is verified in present experimental conditions as well as the relaxation time and diffusion length are estimated to take into account the transient and inhomogeneous nature of the plasma. The optically thin plasma condition is studied by assessing the experimental intensity ratio of atomic lines and compared with that of the theoretical intensity ratio (branching ratio). The signal to noise ratio (SNR) is also obtained as a function of time with respect to laser pulse and incident laser fluence. All these observations indicate that the spectra should be recorded within the temporal window of 1–3.5 µs with respect to laser pulse where the plasma can be treated as optically thin as well as under LTE simultaneously along with the large SNR.

Formation of insufficiently oxidized Cu nanoparticles by laser ablation in organic solvents is correlated with the ablation of the target surface.

The surface scaling behavior of nanostructured Cu thin films, grown on glass substrates by the pulsed laser deposition technique, as a function of the deposition time has been studied using height–height correlation function analysis from atomic force microscopy (AFM) images. The scaling exponents α, β, 1/z and γ of the films were determined from AFM images. The local roughness exponent, α, was found to be ∼0.86 in the early stage of growth of Cu films deposited for 10 minutes while it increased to 0.95 with a longer time of deposition of 20 minutes and beyond this, it was nearly constant. Interface width w (rms roughness) scales with depositing time (t) as ∼ t^β, with the value of the growth exponent, β, of 1.07 ± 0.11 and lateral correlation length ξ following ξ = t^1/z and the value of 1/z = 0.70 ± 0.10. These exponent values convey that the growth dynamics of PLD Cu films can be best described by a combination of local and non-local models under a shadowing mechanism and under highly sticking substrate conditions. From the scaling exponents and power spectral density function, it is concluded that the films follow a mound like growth mechanism which becomes prominent at longer deposition times. All the Cu films exhibited SPR properties where the SPR peak shifts towards red with increasing correlation length (ξ) whereas bandwidth increases initially with ξ and thereafter decreases gradually with ξ.

In the present work, the transient evolution of laser induced plasmas (LIPs) of three different copper alloys are reported in order to identify the optimum temporal window for the implementation of calibration free laser induced breakdown spectroscopy (CF-LIBS) for quantitative analysis. The laser induced plasma (LIP) is generated on the copper alloys in air by focusing the second harmonic of a Q-switched Nd:YAG laser of pulse width ∼7 ns and a repetition rate of 1 Hz. From LIBS spectra it is observed that sample 1 (commercial brass) is comprised of copper (Cu) and zinc (Zn) as the major constituent elements along with the trace elements aluminum (Al), iron (Fe), lead (Pb), tin (Sn) and nickel (Ni), while sample 2 is comprised of Cu, Zn and Ni and sample 3 contains only two elements: Cu and Ni. The accuracy of the CF-LIBS technique depends immensely on the validity of local thermodynamic equilibrium (LTE) and the optically thin condition of the plasma. From the temporal evolution of the LIP, the optimum temporal window is identified where LTE as well as the condition of an optically thin plasma hold together. For this, the temporal evolution of the plasma temperature is studied from the emitted atomic copper transitions via a Boltzmann plot and that of the electron density from the Stark-broadened profile of the CuI (510.5 nm) line. The estimated plasma parameters are used in a one line CF-LIBS algorithm to determine the percentage composition of all the elements present in all three samples. Sample 1, comprising seven elements, is studied first at four different laser energies of 25, 50, 75 and 100 mJ. It is observed that the LTE and optically thin condition of the plasma are well satisfied in the optimum temporal window of 2–4 μs with respect to (w.r.t) the incidence of the laser pulse. The relative errors in the estimation of the concentrations of trace elements are at a minimum at 50 mJ compared to those at other energies. So the other two samples are studied at 50 mJ of laser energy only. The CF-LIBS results within this optimum temporal window for all the samples are also found to be in good agreement with the EDX results.