Measurements of HF-Plasma Oscillations by means of a Laser-Heated Emissive Probe

Indirectly heated emissive probes have advantages compared to conventional emissive wire probes. We have developed a laser-heated emissive probe consisting of a 1 mm diameter and 2 mm long pin of LaB6, heated by a focussed laser beam of 808 nm wavelength with a power up to 50 W. This probe is smaller and simpler than electrically heated emissive wire probes. Materials of low work function, high temperature stability and longer lifetime such as LaB6 can be used. There is no deformation in a magnetic field and no voltage drop along the probe wire. In this contribution we show the good time resolution of such a probe. Whereas emissive wire probes need two cables and an electric power supply or battery, for our probe one connection to an oscilloscope with high input impedance suffices. Therefore the probe system has a much lower stray capacitance than conventional emissive wire probes.