Production of high-density microplasma by microwave excitation and its application to ultra-short-wavelength light

点击翻译按钮获取中文摘要

Research was carried out to inject microwave power into small space and thereby to produce a high-density microplasma continuously, aiming at applying the plasma to a high-brightness ultra-short-wavelength light source. The effect of microwave frequency on the plasma production was also studied. Two types of plasmas were studied: one is "microgap plasma" produced around atmospheric pressure in the microgap (100 μm wide) between two knife-edge electrodes and the other is "micro ECR plasma" produced at low pressures (〜1 Pa) in a microwave stripline with the aid of magnetic field. To study the fundamental properties of plasmas produced, a laser Thomson scattering technique for measuring electron temperature and density in small space was developed. For Ar microgap plasma, a plasma with an electron temperature of 1.2 eV and a high density of 3x10^<14>cm^<-3> was realized with a gas temperature as low as near room temperature. The density of metastable Ar atoms, which are the precursor of VUV light emitting Ar_2 excimer, was measure using laser absorption spectroscopy and the effect of plasma conditions on the Ar_2 excimer formation was clarified; this gives a guide into optimization of the plasma as a VUV excimer light source. Experiments on producing microgap plasma using 10-GHz microwave excitation indicated that reducing the microwave radiation loss is crucial for increasing the electron density, though increasing electron density is expected on the theoretical basis. For micro ECR plasma, 10-GHz excitation showed better plasma localization characteristics, and most measurements were carried out using 10-GHz excitation. Strong Ar^+ emission as well as He^+ emission was observed, indicating the existence of high-energy electrons in the plasma. To increase the plasma density and thereby to obtain variety of short-wavelength emissions from multiply ionized species, improvement of microwave power injection scheme is necessary and is in progress.