Development and application of infrared laser excitation spectroscopy with an array detector

在本研究中，我们的目标是建立一个高灵敏度的红外发射光谱检测系统。迄今为止，对远红外发射的观测主要采用傅里叶变换光谱法。然而，该方法主要局限于双原子分子等物种。由于红外区的发射概率不高，我们考虑了激光激发光谱来观察诱导发射，其中红外激光用于饱和分子的振动-旋转跃迁。本研究的优势之一是利用红外阵列探测器对弱发射光谱进行观测。在35 K的杜瓦瓶中安装了InSb X56 x 256元素的红外阵列探测器。探测器的数据由COGITO-3系统读出，并传送到工作站，由IRAF软件进行分析。检测系统与光栅光谱仪耦合，观测发射光谱。作为激励源，采用市售的12 ~ 80k低温激光元件，建立了红外二极管激光系统。将该系统应用于多径电池吸收光谱，测定了大气中N_2O分子的同位素丰度。由于二极管激光器的输出功率不足以实现振动-旋转的饱和跃迁，因此考虑用量子级联激光器（QC激光器）作为备选激励源。我们与HAMAMATSU HOTONIKUSU进行了合作研究，以研究QC激光器的性能。结果表明，该激光器的输出功率足够大（约100 mW），可用于激光激发光谱学。

In the present study we had an aim to construct a spectroscopic system to detect infrared emission with high sensitivity. So far infrared emission has been observed mainly by Fourier transform spectroscopic method. However, the method is limited to species such as diatomic molecules mainly. Since the probability of emission in the infrared region is not high, we considered laser excitation spectroscopy to observe induced emission, where an infrared laser is used to saturate a vibration-rotational transitions of molecules.One of advantages of the present study is to rise an infrared array detector to observation of weak emission spectra. An infrared array detector with InSb X56 x 256 elements was installed in a dewar of 35 K. Data from the detector were read out by using COGITO-3 system and transferred to a work station and analyzed by an IRAF software. The detection system was coupled to a grating spectrometer to observe emission spectrum.For excitation source, an infrared diode laser system was set up by using commercially available laser elements which operate under low temperature of 12-80 K. The system was applied to absorption spectroscopy by using multi-path cell to determine isotopic abundance ratios of the atmospheric N_2O molecule.The output power of the diode laser was not enough for saturating vibration-rotation transitions, so a quantum cascade laser_(QC laser) is considered as the candidate of excitation source. We carried out a co-operative study with HAMAMATSU HOTONIKUSU to investigate the performance of the QC lasers. It was found that the output power was enough large (about 100 mW) for the present purpose and application to laser excitation spectroscopy has been carried out.