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

研究将微波功率注入小空间，从而连续产生高密度微等离子体，目的是将等离子体应用于高亮度超短波光源。研究了微波频率对等离子体产生的影响。研究了两种等离子体：一种是在大气压下在两个刀口电极之间（100 μm宽）的微间隙中产生的“微间隙等离子体”，另一种是在低压（~ 1 Pa）下在微波带状线中借助磁场产生的“微ECR等离子体”。为了研究等离子体的基本性质，提出了一种用于小空间电子温度和密度测量的激光汤姆逊散射技术。对于Ar微隙等离子体，在接近室温的气体温度下，实现了电子温度为1.2 eV、密度为3x10^<14>cm^< 3>的等离子体。用激光吸收光谱法测定了VUV发光Ar_2准分子前体亚稳Ar原子的密度，阐明了等离子体条件对Ar_2准分子形成的影响；这为等离子体作为VUV准分子光源的优化提供了指导。利用10 ghz微波激发产生微隙等离子体的实验表明，降低微波辐射损耗是提高电子密度的关键，而提高电子密度在理论基础上是可以实现的。对于微型ECR等离子体，10 ghz激励表现出更好的等离子体定位特性，大多数测量采用10 ghz激励进行。观测到强的Ar^+发射和He^+发射，表明等离子体中存在高能电子。为了提高等离子体密度，从而获得多种电离物质的短波发射，改进微波功率注入方案是必要的，并且正在进行中。

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.