Research on the heterodyne spectroscopy in the submillimeter region

对于亚毫米外差光谱技术的发展，亚毫米本振源和低噪声混频器的研究具有重要意义.为了稳定CO_2泵浦亚毫米激光器的功率和频率，这几乎是亚毫米外差激光器的唯一选择，我们研究了两种CO_2激光器的稳频方法，这是实现这一目标的关键;（1）借助于斯塔克调制将泵浦频率锁定到亚毫米激光气体的灯凹陷的技术，（2）使用外部双光束干涉仪锁定泵浦频率的方法，该干涉仪的光程长度由He-Ne塞曼激光器控制。通过这些方法获得了10^量级的频率稳定度<-8>.混频器（1）Nb点接触约瑟夫森结以4波长（4<gamma>）长线天线和角反射器的形式构造。在639 GHz（469）频率下，单边带混频器噪声温度为1660 K，转换效率为-16.8 dB<micrn>。(2)制备了具有长线天线的铅合金SIS结。利用该混频器进行了谐波混频实验。例如，对于693 GHz和139 GHz之间的5次谐波混频，获得43.5 dB的转换损耗。（3）制作了四结串联、带蝶形天线的铌SIS混频器，并将其安装在准光波导中。在337 GHz频率上进行了基频混频实验。证实了基于准粒子的混合已经完成。

For the development of the submm heterodyne spectroscopy, the investigations of submm local oscillators and the low noise mixers are importnat.1. Local oscillators (LO's) To stabilize the power and the frequency of the CO_2 pumped submm laser, which is almost only choice for the submm heterodyne LO's we have developed two methods of CO_2 laser stabilization which is the key for the purpose; (1) A technique to lock the pump frequency to the Lamp dip of the submm laser gas with the aid of the Stark modulation, (2) A method to lock the pump frequency using an external two-beam interferometer of which path length is controlled with a He-Ne Zeeman laser. An frequency stabilization of the order of 10^<-8> was obtained by these methods.2. Mixers (1) The Nb point-contact Josephson junctions were constructed in a form of a 4 wavelength (4<gamma>) long-wire antenna and a corner erflector. A SSB mixer noise temperature of 1660K and a conversion efficiency of -16.8 dB were estimated at 639 GHz (469 <micrn>). (2) The SIS junctions of Pb alloy having a long-wire antenna were fabricated. Some experiments of harmonic mixing were made using the mixers. The conversion loss of 43.5 dB were obtained for the 5th harmonic mixing between 693 GHz and 139 GHz, for example. (3)The Nb SIS mixers with 4 junctions in series and with a printed bow-tie antenna, was fabricated and they were mounted in a quasi-optical beam guide. An experiment of fundamental mixing was carrierd out at 337 GHz. It was confirmed that the mixing based on the quasi-particle was done.