Development of Measuring CO_2 Concentration by Laser Induced Multiphoton Fluorescence

为了制定应对全球变暖的对策，需要发展co2浓度的非侵入式测量技术。例如，它可以应用于直接喷射发动机系统，减少30%的二氧化碳。在本研究中，我们开发了一种多光子吸收型激光诱导荧光测量技术。将355nm （3.5eV）的高功率脉冲YAG激光聚焦到一个电池中，其中规定浓度的CO_2气体和氮气流过电池。激光诱导荧光光谱强度的检测采用单色仪和CCD二极管相机，并配有图像增强器。CO2分子被激发成更高水平的C、CO、CO_+和CO_<2+>，并检测到特征激光诱导荧光光谱。明确了LIF的作用机理。阐明了CO_2浓度对激光诱导荧光强度的影响。此外，还对激光强度和压力对现有测量技术的影响进行了阐述。目前的技术要求激光脉冲能量大于200mJ/脉冲。压力条件不需要很低，该方法适用于常压条件。在高功率激光的作用下，氮离子也被分解成N_+，且随着氮离子浓度的降低，其光谱幅度减小。由于N_+与CO_<2+>的比值仅仅是CO_2浓度的函数，因此这种现象可以应用于一种不考虑激光功率波动和CCD二极管阵列灵敏度的先进测量技术。

In order to develop strateges for global warming, it is needed to develop non-intrusive measurement technique of CO_2 concentration. It can be applied, for example, direct injection engine system which reduces CO_2 for 30 percent. In the present study, we developed a measurement technique using multiphoton absorption type laser induced fluorescence. A high-power pulse YAG laser light of 355nm (3.5eV) was focussed into a cell, where prescribed CO_2 concentration gas with Nitrogen flows through it. The laser induced fluorescence spectrum intensity was detected by an monocromator and CCD diode camera equipped with an image-intensifier. CO2 molecules was excited into a higher level of C,CO,CO_+ and CO_<2+> and characteristic laser induced fluorescence spectrum was detected. The mechanism of LIF was made clear. Effect of CO_2 concentration on the laser induced fluorescence intensity was clarified. In addition, laser intensity and pressure on the present measurement technique was elucidated. The present technique requires laser pulse enery larger than 200mJ/pulse. The pressure condition needs not to be low and the presetn method could be applied in atmospheric pressure condition. The nitrogen is also breaks into N_+ by the high power laser and the magnitude of its spectrum reduces when concentration of nitrogen becomes low. Its phenomena could be applied to an advanced measurement technique without considering laser power fluctutation and sensitivity of CCD diode array since the ratio of N_+ to CO_<2+> becomes only a function of CO_2 concentration.