• S Chaurasia

      Articles written in Pramana – Journal of Physics

    • Laser interaction with low-density carbon foam

      S Chaurasia S Tripathi D S Munda G Mishra C G Murali N K Gupta L J Dhareshwar A K Rossall G J Tallents Rashmi Singh D K Kohli R K Khardekar

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      Experiments were performed with a 15 J/500 ps Nd:glass laser ($\lambda = 1064$ nm) focussed to an intensity > 1014 W/cm2 . X-ray emissions from carbon foam and 5% Pt-doped carbon foam of density 150–300 mg/cc were compared with that of the solid carbon targets. The thickness of the carbon foam was 15 𝜇m on a graphite substrate. X-ray emission was measured using semiconductor X-ray diodes covered with various filters having transmissions in different X-ray spectral ranges. It covered X-ray spectrum of 0.8–8.5 keV range. The X-ray emission in the soft X-ray region was observed to increase to about 1.8 times and 2.3 times in carbon foam and Pt-doped foam, respectively with respect to solid carbon. In hard X-rays, there was no measurable difference amongst the carbon foam, Pt-doped carbon foam and solid carbon. Scanning electron microscope (SEM) analysis demonstrates that foam targets smoothens the crater formed by the laser irradiation.

    • Dynamic imaging and hydrodynamics study of high velocity, laser-accelerated thin foil targets using multiframe optical shadowgraphy

      S Tripathi S Chaurasia P Leshma L J Dhareshwar

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      The main aim of the study of thin target foil–laser interaction experiments is to understand the physics of hydrodynamics of the foil acceleration, which is highly relevant to inertial confinement fusion (ICF). This paper discusses a simple, inexpensive multiframe optical shadow-graphy diagnostics developed for dynamic imaging of high velocity laser-accelerated target foils of different thicknesses. The diagnostic has a spatial and temporal resolution of 12 𝜇m and 500 ps respectively in the measurements. The target velocity is in the range of $10^{6} - 10^{7}$ cm/s. Hydrodynamic efficiency of such targets was measured by energy balance experiments together with the measurement of kinetic energy of the laser-driven targets. Effect of target foil thickness on the hydrodynamics of aluminum foils was studied for determining the optimum conditions for obtaining a directed kinetic energy transfer of the accelerated foil. The diagnostics has also been successfully used to study ablatively accelerated targets of other novel materials.

    • Development of online quasimonochromatic X-ray backlighter for high energy density physics studies

      S Chaurasia P Leshma D S Munda

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      Monochromatic X-ray backlighting has been employed with great success in various laser plasma experiments including inertial confinement fusion (ICF) research. However, implementation of a monochromatic backlighting system typically requires extremely high quality spherically bent crystals which are difficult to manufacture and are also expensive. In this paper, we present a quasimonochromatic X-ray backlighting system using flat thallium acid pthalate (TAP) crystal. The detailed characterization of the system is discussed. The X-ray backlighter spectral range is caliberated using Cu spectrum in the spectral range 7–9 Å (1.38–1.77 keV). Gold plasma produces continuous X-ray spectrum (M band) in this range. The spectral, spatial and temporal resolutions of the system measured are 30 mÅ, 50 $\mu$m and 1.5 ns respectively. The spectral width of the X-ray pulse is 2 Å ($\Delta E$ = 0.39 keV).

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