Laser light scattering diagnostics of high-pressure microgap discharge

A preliminary study of a microgap discharge aiming at CW excimer laser medium was carried out. Stable CW glow discharge was produced between knife-edge electrodes separated by ∼100 µm in atmospheric air by microwave (2.45 GHz) excitation. The plasma in the microgap was investigated by laser light scattering. A special triple-grating spectrometer with sharp notch characteristics for eliminating Rayleigh and stray scattering components was employed. When the discharge was absent, clear rotational Raman scattering due mainly to N2 molecules was observed; however, it almost disappeared when the discharge was turned on, indicating a high gas temperature (>∼3000 K) in the microgap. At a microwave power of 100 W, Thomson scattering signal was below a noise level, suggesting a electron density of <∼2×10¹⁴ cm⁻³.