POPURATION INVERSION IN FLAME EXCITED BY MICROWAVE FOR COMBUSTION DERIVED LASER EMISSION

高功率、高效率激光器的研制是激光电源工业化应用的必要条件。传统激光器的激发仅依赖于电功率。这样的激光器不仅需要巨大的电力以发射高功率，而且难以引入利用除了用于激光发射的有效能量之外的能量的系统。为了开发利用燃料燃烧能和辅助电能产生高功率激光的高效系统，研究了微波强化陶瓷燃烧器中甲烷-空气混合气燃烧的激光发射原理。结果表明，假设的玻尔兹曼分布的分子能级的扰动。用CO_2激光器探测到一个小信号增益，它代表了入射光束在介质中的放大程度。当用频率为2.45GHz的微波辐照燃烧区时，两个MCT光电探测器的信号比增加，表明波长为10.6 μm的红外辐射被放大。另一方面，用傅立叶变换红外光谱（FT-IR）分析了微波作用下火焰对红外辐射的吸收，发现H_2O和CO_2分子在2.7 μ m和4.2 μm波段的吸收受微波激发能级效应的影响，使能级以上的分子布居数大于热力学平衡态。此外，这种效应也被拉曼光谱分析所证实。这些事实暗示了微波辐照燃烧产生激光辐射的可能性。

Development of high power and high efficient laser is necessary for introducing industrial applications of laser power. Excitation of the conventional lasers is dependent of only electric power. Such lasers don't only require huge electricity in order to emit a high power, but also it is difficult to introduce a system utilizing energy except for the effective energy for laser emission. The objective of this work is to develop the efficient system of a high power laser derived by combustion energy of fuels and/or auxiliary electricity for manufacturing.Microwave enhanced combustion of methane-air mixture in a ceramic burner is studied to examine the principle of a new laser emission. The results suggest perturbation of the assumed Boltzmann distribution of molecular energy levels. A small signal gain, which represents the level of amplification of an incident beam in a medium, was detected using a CO_2 laser. An increase in the signal ratio of two MCT photodetectors when the combustion zone was irradiated by microwave of 2.45 GHz in the frequency indicates amplification of infrared radiation at 10.6 μm in wavelength. On the other hand, absorption of infrared radiation in the flame irradiated by microwave was analyzed spectroscopically by the FT-IR. The absorption in 2.7 and 4.2 μm bands of H_2O and CO_2 molecules was influenced by the effect of excitation to energy levels by microwave so that the population of molecules at upper energy levels than the grand level becomes greater than a thermo-dynamic equilibrium state. In addition, this effect was confirmed by Raman spectroscopic analysis as well. These facts imply the possibility of combustion derived laser emission by irradiation of microwave.