Detection of density jump in laser-induced shock wave plasma using a rainbow refractometer

A special interferometric technique with high sensitivity has been devised on the basis of rainbow refractometry without the use of an additional and delicate amplitude-splitting setup. This new technique was used for the cha racterization of shock wave plasma induced by a Q-switched Nd:YAG laser on various metal samples under reduced surrounding gas pressures. An unmistaka ble signal of the density jump was detected simultaneously with the observa tion of the emission front signal. It proved that the emission front and th e front of the blast wave coincided and moved together,vith time at the ini tial stage of the secondary plasma expansion. However, at a later stage, th e emission front began to separate from and left behind the blast wave fron t propagating in the surrounding gas at low pressures. With the use of Cu a nd Zn samples, the experimental results showed that the separation of the e mission front and blast wave front took place at about 5 mm above sample su rface for laser energy of 140 mJ.