• M Krishnamurthy

      Articles written in Pramana – Journal of Physics

    • Impurities good and bad: Doped cluster nanoplasmas in intense laser fields and characterization of impurity level

      J Jha M Krishnamurthy

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      Doping of cluster-based targets can bring out considerable modifications in the evolution of the nanoplasma formed from clusters in intense laser fields. The consequence could be either an increase or, a decrease (depending upon the properties and proportion of the dopant) in the emission of the resulting charge particles or photons from nanoplasma. As we can control the percentage of CS2 in the doped Ar-CS2 cluster, we can have argon-doped CS2 cluster (when argon constitutes about 10–40%) and CS2-doped argon cluster (when fraction of CS2 is 10–40%). In the experimental studies of electron spectra and X-ray emission from pristine Ar$_{n}$ ($n \leq 25, 000$) and doped Ar-CS2 clusters at laser intensities of about 1015 W cm-2, it is observed that there is more than an order of magnitude enhancement in those emissions in doped Ar-CS2 clusters than in the former case. Conversely, a significant reduction in those emissions was found in the latter case. Such observations signify the importance of characterization of these targets. In this direction, we demonstrate a simple method for the characterization of doping level based on the Rayleigh scattering measurements.

    • Surface roughness-aided hard X-ray emission from carbon nanotubes

      Suman Bagchi P Prem Kiran M K Bhuyan M Krishnamurthy K Yang A M Rao G Ravindra Kumar

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      Efficient low debris hard X-ray source based on multiwalled carbon nanotubes (MWNT) irradiated by intense, femtosecond laser over an intensity range of $10^{15} –10^{17}$ W cm$^{−2} \mu𝑚^{2}$ is reported. The MWNT targets yield two orders of magnitude higher X-rays (indicating significant enhancement of laser coupling) and three orders of magnitude lower debris compared to conventional metallic targets under identical experimental conditions. The simple analytical model explains the basic experimental observations and also serves as a guide to design efficient targets to achieve low-debris laser plasma-based hard X-ray sources at low laser intensities suitable for multi-kHz operation.

    • Probing strong field ionization of solids with a Thomson parabola spectrometer

      Malay Dalui T Madhu Trivikram Ram Gopal M Krishnamurthy

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      Intense ultrashort laser pulses are known to generate high-density, high-temperature plasma from any substrate. Copious emission of hot electrons, from a solid substrate, results in strong electrostatic field that accelerates the ions with energies ranging from a few eV to MeV. Ion spectrometry from laser–plasma is convolved with multiple atomic systems, several charge states and a broad energy spread. Conventional mass spectrometric techniques have serious limitations to probe this ionization dynamics. We have developed an imaging ion spectrometer that measures charge/mass-resolved ion kinetic energies over the entire range. Microchannel plate (MCP) is used as the position-sensitive detector to perform online and single shot measurements. The wellresolved spectrum even for the low-energy ions, demonstrates that the spectral width is limited by the space-charge repulsion for the ions generated in the hot dense plasma.

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