Faculty Publications

Now showing 1 - 4 of 4

Effect of laser beam size on the dynamics of ultrashort laser-produced aluminum plasma in vacuum
(American Institute of Physics Inc. subs@aip.org, 2019) Sankar, P.; Shashikala, H.D.; Philip, R.
In laser-produced plasma experiments, the diameter of the irradiating laser beam on the target surface is a major parameter that influences the ablation mechanisms, plasma emission intensity, charged particle ejection, and plume morphology. In this work, the expansion dynamics of an ultrashort laser-produced aluminum plasma is investigated as a function of the laser beam size on the target, using a combination of diagnostic tools, viz., optical emission spectroscopy, fast gated time-resolved imaging, and ion current measurements. A Ti:sapphire laser delivering 100 fs, 6 mJ pulses at 800 nm is used for producing plasma from a pure Al target placed in vacuum (10 -5 Torr) at different positions with respect to the geometrical focus of the beam. Optical emission spectroscopic analysis of the plasma shows that higher emission intensities and ion populations are obtained for smaller beam sizes. Time-resolved Intensified Charge Coupled Device (ICCD) imaging of the expanding plasma shows a spherical morphology for plumes produced by smaller beam sizes and a cylindrical morphology for those produced by larger beam sizes. Temporal profiles of ion emission measured using a Faraday cup are in agreement with ICCD data, featuring a dual peak structure for larger beam sizes indicating distinct slow and fast ionic species, arising from changes in the ablation mechanism for varying laser fluences. Plume expansion is modelled by free expansion for the fast species and by shock wave propagation for the slow species. Ion flux and velocities are relatively high for smaller beam sizes. These studies can be of potential importance for laser processing applications, including laser welding, drilling, and micromachining. © 2019 Author(s).
High-temperature wear and frictional behavior of partially oxidized Al with NiCr composite coating
(Institute of Physics Publishing helen.craven@iop.org, 2019) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.
The influence of composite coating in improving wear and frictional behavior from room temperature to 600 °C was investigated. Partially oxidized Al powder was prepared with a flame spray process by spraying pure Al powder into distilled water. The composite powder is the mixture of 30 weight percent of partially oxidized Al and 70 weight percent of NiCr alloy powder. The composite powder was subsequently coated on MDN321 steel by air plasma spray process. The composite coatings are characterized with respect to adhesion strength, porosity, micro-hardness, and density. Wear and frictional behavior of coatings are evaluated under disc speed of 1 and 2 m s-1, loads of 10, 20 and 30 N and 3000 m sliding distance. The test results indicated that at room temperature, frictional heat generated due to applied load produce three-body abrasion at the interface caused to increase the wear and friction in the coating. The oxide film formed at high temperature due to plastic deformation avoids surface degradation at the interface and reduce the wear and friction. The worn surfaces at 600 °C consist phases of ?-Al2O3, NiO, and Cr3O. These phases are contributing to improving the wear resistance of the coating more than 4-times compared to uncoated steels under varying load and sliding velocities. The coefficient of friction reduced with increase in temperature due to generated oxides act as lubricants at the interface. © 2019 IOP Publishing Ltd.
Large magnetoresistance in a Co/Mo S2/graphene/Mo S2/Co magnetic tunnel junction
(American Physical Society, 2021) Devaraj, N.; Tarafder, K.
We demonstrate a large magnetoresistance (MR) in a Co/MoS2/graphene/MoS2/Co magnetic tunnel junction by means of ab initio transport calculations. A Co electrode turns out to be an excellent spin injector for a MoS2/graphene/MoS2 barrier. The transmission spectrum, current-voltage characteristics, spin injection efficiency, and magnetoresistance are calculated for the modeled device at various bias voltages in the parallel and antiparallel magnetic configurations. A remarkable change in the transmission spectrum and a subsequent change in total current through the junction have been observed, when the relative magnetic orientations of the electrodes are altered. The huge change in current due to the change in the relative magnetic orientation of the Co electrodes produces a high magnetoresistance up to 1270%. The obtained values of the device parameters clearly indicate that a MoS2/graphene/MoS2 heterostructure would be an excellent compound for highly efficient spin-valve device applications. © 2021 American Physical Society.
Temperature Detection Using Plasmonic Waveguide Ring Resonator: Design and Analysis
(Institute of Electrical and Electronics Engineers Inc., 2024) Nausheen, T.A.; Nikhilesh Kumar, C.; Khanna, A.; Singh, M.
A 3-D-hybrid plasmonic waveguide (HPWG) cascaded ring resonator-based temperature sensor is studied in the infrared (IR) spectral regime. The proposed design achieves high sensitivity and precision in temperature measurements by integrating the unique properties of plasmonic and photonics. The HPWG enhances the interaction between the optical field and the surrounding environment, while the cascaded ring resonators provide a compact and efficient means of modulating the optical signal in response to temperature changes. Our theoretical analysis and numerical simulations demonstrate that the device exhibits a significant shift in resonance wavelength with temperature variations, leading to an enhanced sensitivity (0.37 nm/K) compared to traditional photonic sensors. The potential applications of this temperature sensor span various fields, including environmental monitoring, biomedical diagnostics, and industrial process control. It offers a promising solution for advanced temperature sensing with improved performance and miniaturization. © 1973-2012 IEEE.

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