Dynamics of Collinear Counterpropagating Laser Plasmas under Ambient Atmospheric Conditions

A numerical study of interaction of two counter propagating laser induced atmospheric air plasmas separated by a distance of 4 mm using FLASH
¹
2D radiation hydrodynamic code is presented. The plasma dynamics and the subsequent shock wave expansion were validated with the experimental results show a good agreement. Second harmonic laser pulses from Q-switched Nd:YAG laser (TITAN-5, 5J, 10 ns, 5 Hz, M/s. Amplitude Technologies) were used to create two plasma sources (S
1
& S
2
) due to 50 and 100 mJ pulse energies, respectively. The interaction of the two freely expanding plasmas is initiated at
$0.9\ \mu \mathrm{s}$
, leading to the formation of soft stagnation layer at the interaction zone. During the interaction of two plasmas a maximum mass density (
$4.7\times 10^{-3}$
gm/cc) and pressure (2.2 MPa) were observed at stagnation layer over a time duration of
$1.1\ \mu\mathrm{s}$
. This density and pressure are more than the sum of the individual sources before interaction. A density drag is observed in the source S
1
beyond 1.1 µs because of the penetration of the SW from high energy source (S
2
) leading to formation of a plasma jetlet. The spatio-temporal evolution of the plasma, shockwave and plasma jetlet dynamics were discussed in terms of the plasma density (n
e
), temperature (T
e
) and the pressure of individual plasma sources leading to the evolution of plasma jetlet. These colliding plasma plumes are useful to understand the shockwave - plasma interaction
²
.