When plasma embeded in the magnetic field was driven magnetically, Magnetohydrodynamic shock wave was formed. The maximum speed of the front wns 5.6cm/μs. The preheating of the gas is a very important factor to produce this kind of shock wave. The observed data and calculation show that the plasma behind the front is in almost collisior less state. But it seems hardly to say that the observed shock is mainly caused by the collisionless mechanism.
Laser is a very suitable light source of the interferometer. The advantages of the use of a laser come from the excellent coherency or long coherent length, good monochromaticity and high intensity. We have measured the density of shocked plasmas by using Mach-Zehnder interferometer with He-Ne gas laser. This device seems to be very powerful to investigate fast transient phenomena in high electron density such as plasma shock waves. The precise experiments are going on.