Development of Wideband Terahertz Emission Spectroscopy by using heterodyne receiver

本研究的目的是利用外差探测技术建立太赫兹区域的气相发射光谱。该方法能够采集宽带频谱（1000-4000 MHz），而不会降低传统吸收光谱（100 kHz或更低）所获得的频率精度。为了展示这些优势，我们展示了以下三点；1. 对压力展宽光谱进行光谱测量，讨论其形状并推导压力展宽或位移参数。2. 易于分配的分子跃迁显示一个复杂的光谱模式；多重或同时的量子态观察。本研究的实验装置是在日本宇宙航空研究开发机构（JAXA）位于筑波空间中心的超导接收系统上，工作在0.6 thz。首先，我们成功地测量了氯化氢分子的两种同位素体在0.3 ~ 200 hPa的压力范围内J=1-0旋转跃迁的发射光谱。通过分析观察到的发射光谱的形状，可以推导出分子对氮和氧的压力展宽和压力位移参数。对乙腈分子也进行了同样的测量，乙腈分子在对流层化学中被认为是重要的。可靠的压力加宽和位移参数将有助于通过遥感技术从观测到的大气光谱中获取分子的丰度。我们还尝试检测通过释放乙腈分子和氦的混合物获得的等离子体的发射光谱。对放电反应产物氰化氢的振动激发态进行了观察。我们的方法可以估计分子的振动温度约为410 K。这些信息将有助于分子动力学的研究。这些结果将发表在《分子光谱学杂志》上。少

The purpose of this study is to develop gas-phase emission spectroscopy at terahertz region by using heterodyne detection technique. The method has a capability of taking a wideband frequency spectra (1000-4000 MHz) without degrading frequency accuracy obtained in the conventional absorption spectroscopy (100 kHz or less). We demonstrated the following three points in order to demonstrate these advantages; 1. Spectroscopic measurements of pressure-broadened spectra to discuss its shape and derive pressure broadening or shift parameters. 2. Easy assignments of transitions of the molecule showing a complicated spectral pattern, and 3. Multiple or simultaneous quantum states observation. The experimental setup used in the present study is a superconducting receiver system at JAXA in Tsukuba Space Center operated at 0.6 THzFirst, we have succeeded to measure emission spectra of J=1-0 rotational transition of the two isotopomers of the hydrogen chloride molecule in the pressure range betwee … More n 0.3 to 200 hPa. Pressure broadening and pressure shift parameters against nitrogen and oxygen for the molecule can be derived by analyzing the shape of the observed emission spectra. The same kind of measurements was also conducted for the acetonitrile molecule, which is considered to be important in the tropospheric chemistry. Reliable pressure broadening and shift parameters will contribute to retrieve abundance of the molecule from the observed atmospheric spectra by remote sensing techniqueWe have also tried to detect emission spectra from the plasma obtained by discharging a mixture of the acetonitrile molecule and helium. The hydrogen cyanide, one of the reaction products produced by a discharge, is observed with its vibrational excited state. Our method makes it possible to estimate of the vibrtional temperature of the molecule to be approximately 410 K. This kind of information will contribute to kinetic study of the molecules.These results will be published in the Journal of Molecular Spectroscopy. Less