7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Short Pulse Interaction with Droplet Generated Microplasmas
1

Animesh Sharma1 and Amita Das1
Department of Physics, Indian Institute of Technology Delhi, New Delhi
e-mail (speaker): animeshsharmaresearch@gmail.com

Interaction of non relativistic femtosecond(fs) pulses
with spatially confined plasmas, generated frommicrodroplets, have recently been used to generateenergetic electrons. [1], [2]The production of hot electrons
conventionally requires long duration (ps-ns) and highenergy pulses(J-kJ) to create an extended region of
inhomogeneous plasma and sufficient time for
instabilities due to two plasmon decay (TPD) andstimulated Raman scattering (SRS) to grow which canaccelerated electrons to high energies[3–7]. If these
conditions are achieved using fs duration, mJ energy,
kHz repetition rate pulses then hot electron production
may be achieved using table top facilities. The
understanding of the production of hot electrons
possessing energy of the order of 100keV with mJ, nonrelativistic fs pulses with micro-plasma remains elusive.
TPD mechanism has been proposed due to detection of
3/2 harmonic of laser frequency.[2], [8]Our work here is aimed at understanding theunderlying normal modes and parametric processes
which may arise in the context of such finite plasmas.
Thus, we have chosen a simple set-up of a microdroplet
interacting with fs laser for our study. Numericalsimulations were performed using 2D Particle in Cell
(PIC) code EPOCH.[9] The simulation domain consistedof 50 × 50 µm2 and had 3000 × 3000 cells with 8 macro
particles per cell. The micro plasma was of 30
dia. In
theplasma,forfor
andfor r>15
(r is the radius ofmicroplasma centered at 25,25) and A Gaussianlaser propagating along X axis with beam waist of 20µm dia., with full width half maximum (FWHM) pulse
duration 25 fs, having peak intensity of 5.28 × 1017
W/cm2 and corresponding a0= 0.5 was made to interact

with such a micro plasma.
Figure 1.a presents the electron number density after
the interaction of laser pulse with target plasma. It showselectrons emerging symmetrically at an angle of about
22o from the beam axis. In Figure 1.b. the electronenergy has been depicted. The maximum energy isshown to be around ~380keV. An understanding of theobservations will be provided.
The authors thank IIT Delhi HPC facility forcomputational resources. The financial support for thiswork from DST and SERB for grants CRG/2022/002782
and JCB-000055/2017 is acknowledged.
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References[1]M. Anand, P. Gibbon, and M. Krishnamurthy, Laser
Phys., vol. 17, no. 4, pp. 408–414,p. 83105, 2007.
[2]P. K. Singh, A. Adak, A. D. Lad, G. Chatterjee, and G.
R. Kumar, Phys. Plasmas, vol. 27, no. 8, 2020.
[3]N. A. Ebrahim, H. A. Baldis, C. Joshi, and R. Benesch,Phys. Rev. Lett., vol. 45, no. 14, pp. 1179–1182, 1980.
[4]T. J. M. Boyd, Plasma Phys. Control. Fusion, vol. 28,p. 1887, 1887.
[5]C. S. Liu and M. N. Rosenbluth, Phys. Fluids, vol. 19,
no. 7, pp. 967–971, 1976.
[6]P. K. Kaw, “Nonlinear laser–plasma interactions,” Rev.
Mod. Plasma Phys., vol. 1, no. 1, pp. 1–42, 2017.
[7]T. Tajima and J. M. Dawson, “Laser electronaccelerator,” Phys. Rev. Lett., vol. 43, no. 4, pp. 267–270,
1979.
[8]I. N. Tsymbalov, D. A. Gorlova, V. Y. Bychenkov, andA. B. Savel’ev, Quantum Electron., vol. 49, no. 4, pp.
386–390, 2019.
[9]T. D. Arber et al., Plasma Phys. Control. Fusion, vol.
57, no. 11,p. 113001, 2015.

a)b)
Figure 1. The a) number density of electrons and b) mean particle energy at t=80fs.The bunching of electrons is seen at
symmetrical locations in the backward scattering direction (Y=25. Highest energy reached is ~380 keV