Invasiveness of picosecond and nanosecond laser diagnostics on plasma bullets in N2

Laser diagnostics are widely used to obtain plasma characteristics. For example, Thomson scattering is applied for determining the electron temperature and density and recently E-FISH (electric field induced second harmonic generation) was introduced as a method to directly obtain the electric field. So far, laser diagnostics were considered non-invasive. In this research, we will show the effect of a focused pulsed laser beam crossing the path of a plasma bullet in nitrogen flowing into atmospheric air. The laser beam ionizes part of the molecules and atoms along its focus. Therefore, the bullet branches when entering the beam path.The new, simple and promising E-FISH technique is applied to the plasma to obtain its electric field. In E-FISH, a laser beam interacts non-linearly with the ambient electric field in a medium, which results in frequency doubled light. The intensity of these second harmonics scales quadratically with the electric field. In this way, a polarization resolved electric field distribution can be obtained for (almost) any kind of plasma. A nano- and a picosecond pulsed laser are used as a source. For the first time, the obtained field profiles measured with both lasers are compared to each other and the effect of the laser beam on the plasma is examined by using an ICCD camera. This work unfolds a direct correspondence of the determined electric field profile obtained with the nanosecond laser and the branching of the bullet.