Expansion kinetics of shock waves generated by laser ablation in copper across a transverse magnetic field

Spatio-temporal evolution of laser-induced shock wave (LISW), initiated by 6 ns laser ablation of Cu target in a transverse magnetic field (B) of diverse strength was investigated by optical beam deflection method. It was found that the average LISW velocity in the near field achieve a value 2.8 km/s which dropped to 2.1 km/s in the absence of B. The shock wave pressure near the target surface at the highest incident fluence reaches50 MPa for applied B = 300 mT and nearly become halved without B. The decay of the near field shock front pressure estimated from the Sadowski shock-wave approximation pointed to a strong attenuation mechanism in the initial phase of the shock wave propagation. Interestingly, the shock wave front pressure swiftly increases with gradual increase of incident fluence that finally starts to saturate at high fluence regardless of applied B. The development of shock wave was further mapped with laser ablation of Cu target under transverse B. The ablation depth is found to enhance gradually with increase of B (0-300 mT) which could be attributed to the increase in plasma temperature under B.