Interaction of counter propagating laser induced shockwaves in atmospheric air*

The spatio-temporal evolution of colliding ns laser induced shockwaves by varying the laser energy and the separation between the laser plasma sources (0.5 -- 10 mm) is presented. The input laser energy at one point is fixed to 25 mJ, whereas the other side is varied from 25 - 96 mJ. The plasma and shock wave interaction dynamics were observed to vary with varying energy deposition and distance between the two sources. The shock and contact fronts at the interaction zone between the two counter propagating LISW have showed interesting features. At initial time scales (\textasciitilde 1.6 \textmu sec) the plasma plumes have started interacting with each other that evolved into a stable bright interaction zone with increased intensity. Around 4 -- 8 \textmu sec two SW's are trying to propagate through each other resulting in quasi stable localized energy zone. At longer time scales \textgreater 20 \textmu sec, higher energy source propagates through the lower energy one leading to a discontinuity. These interaction dynamics are compared with the SWs from individual plasma sources to explicitly bring out the effect of interacting plasma sources on the SWs propagating into atmosphere.