• A Chowdhury

      Articles written in Pramana – Journal of Physics

    • Optimization of soft x-ray line emission from laser-produced carbon plasma with laser intensity

      A Chowdhury R A Joshi G P Gupta P A Naik P D Gupta

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      Absolute measurement for He-α resonance (1s21S0−1s2p1P1, at 40.2 Å) line emission from a laser-produced carbon plasma has been studied as a function of laser intensity. The optimum laser intensity is found to be ≈1.3×1012 W/cm2 for the maximum emission of 3.2 × 1013 photons sr−1 pulse−1. Since this line lies in the water window spectral region, it has potential application in x-ray microscopic imaging of biological sample in wet condition. Theoretical calculation using corona model for the emission of this line is also carried out with appropriate ionization and radiative recombination rate coefficients

    • Effect of dielectronic recombination on the charge-state distribution and soft X-ray line intensity of laser-produced carbon plasma

      A Chowdhury G P Gupta P A Naik P D Gupta

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      The effect of dielectronic recombination in determining charge-state distribution and radiative emission from a laser-produced carbon plasma has been investigated in the collisional radiative ionization equilibrium. It is observed that the relative abundances of different ions in the plasma, and soft X-ray emission intensity get significantly altered when dielectronic recombination is included. Theoretical estimates of the relative population of CVI to CV ions and ratio of line intensity emitted from them for two representative formulations of dielectronic recombination are presented.

    • Optimization of C5+ Balmer-𝛼 line intensity at 182 Å from laser-produced carbon plasma

      A Chowdhury R A Joshi P A Naik P D Gupta

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      Parametric dependence of the intensity of 182 Å Balmer-𝛼 line $(C^{5+}; n = 3 \rightarrow 2)$, relevant to xuv soft X-ray lasing schemes, from laser-produced carbon plasma is studied in circular spot focusing geometry using a flat field grating spectrograph. The maximum spectral intensity for this line in space integrated mode occurred at a laser intensity of $1.2 \times 10^{13}$ W cm-2. At this laser intensity, the space resolved measurements show that the spectral intensity of this line peaks at $\sim 1.5$ mm from the target surface indicating the maximum population of C5+ ions $(n = 3)$, at this distance. From a comparison of spatial intensity variation of this line with that of C5+ Ly-𝛼 $(n = 2 \rightarrow 1)$ line, it is inferred that $n = 3$ state of C5+ ions is predominantly populated through three-body recombination pumping of C$^{6+}$ ions of the expanding plasma consistent with quantitative estimates on recombination rates of different processes.

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