Volume 80, Number 2, October 2007
Article Number 25002
Number of page(s) 5
Section Physics of Gases, Plasmas and Electric Discharges
Published online 14 September 2007
EPL, 80 (2007) 25002
DOI: 10.1209/0295-5075/80/25002

Laser absorption in microdroplet plasmas

M. Anand1, P. Gibbon2 and M. Krishnamurthy1

1  Tata Institute of Fundamental Research - 1 Homi Bhabha Road, Mumbai 400 005, India
2  John-von-Neumann Institute for Computing, ZAM, Forschungszentrum Jülich - D-52425 Jülich, Germany

received 19 June 2007; accepted in final form 24 August 2007; published October 2007
published online 14 September 2007

We present experimental measurements of the absorption of ultrashort laser pulses by 15 $\mu$m diameter methanol microdroplets. The droplet absorbs upto 70% of the incidence laser energy in the presence of a prepulse at intensities of about 1.5 $\times$ 1016 W cm-2. In the absence of a prepulse, the absorption is only about 20%. Simultaneous measurements of X-ray yield (12 keV to 350 keV) and the absorption in the droplet plasma, shows that our earlier measurements of efficient generation (Anand M. et al. Appl. Phys. Lett., 88 (2006) 181111) of hard X-rays from the droplet plasma is due to the increased absorption in the droplets in the presence of optimum prepulse. 1-D PIC simulations, mimicing the mass-limited droplet density profile, demonstrate the effectiveness of the large scale-length droplet plasma in providing optimal conditions for resonant laser absorption energy and generation of hot electrons.

52.38.Ph - X-ray, $\gamma$-ray, and particle generation.
52.25.Os - Emission, absorption, and scattering of electromagnetic radiation.
79.20.Ds - Laser-beam impact phenomena.

© Europhysics Letters Association 2007