Optical measurement of the expansion of a laser plasma created on a planar microtarget

摘要

Interferometric density measurements in the corona of a laser created plasma require small targets in order to reach the highest density possible. Here we have chosen to create the plasma on the end of microcylinders which diameter is of the size of the focal spot of the laser. With this type of target, the plasma created outside the focal spot of the laser by lateral conduction is located at the periphery of the microcylinder and can be optically probed separately from the main plasma. Using such targets illuminated with a 1-3 J, 50 ps duration neodymium laser pulse, we have evidenced during the laser pulse non linear effects such as density profile modifications and filamentation. After the laser pulse, we have measured the density distribution showing that the density contours are nearly spherical. A few percent of the incident laser energy is found in a lateral plasma whose temperature is a few electron volts and which expands about 100 μm along the microcylinder.