Investigations on Electric Field Distributions in a Microwave Discharge in Hydrogen

Introduction Microwave discharges play an important role in plasma sources for industrial applications like surface modification and thin film deposition. The electric field distribution in the plasma determines the electron density and energy distribution and the homogeneity of the discharge. The typical amplitude of the electric field is of the order of 100 V/cm. Up to now, this low field strength was not within the reach of laser spectroscopic techniques for electric field measurements. Recently, we have developed a novel technique in atomic hydrogen that allows the measurement of low electric fields down to 5 V/cm. The electric field is determined from the Stark splitting of high Rydberg states. (typically n = 14 20). Here, this technique is applied to a pulsed microwave discharge at 2.45 GHz in hydrogen with a 10 % argon admixture. The spatial and temporal field distribution is investigated in a commercial plasma source (SLAN). For the first time, we can measure both the microwave field and the microfield, originating from the plasma charges by a laser spectroscopic technique with high spatial and temporal resolution.