We describe the generation of far-infrared radiation using an optically pumped molecular laser along with the measurement of their frequencies with heterodyne techniques. The experimental system and techniques are demonstrated using difluoromethane (CH2F2) as the laser medium whose results include three new laser emissions and eight measured laser frequencies.
的产生和远红外线辐射的随后的测量发现在高分辨率光谱,射电天文学,和太赫兹成像众多应用。约45年,连贯,远红外辐射的产生使用光泵分子激光器已经完成。一旦远红外激光辐射被检测到,这些激光辐射的频率被用三激光外差技术测量。利用这种技术,该未知频率从光泵浦分子激光器是具有两个稳定的,红外线参考频率之间的差频混合。由独立的二氧化碳激光器生成这些基准频率,每个稳定来自外部,低压参考细胞使用荧光信号。的已知和未知的激光频率之间所产生的跳动是由一个金属 – 绝缘体 – 金属点接触二极管检测器,其输出上的规格观察监视特鲁姆分析仪。这些激光排放之间的拍频随后测量并结合已知的参考频率来推断未知远红外激光频率。与此技术测量的产生的一种-Σ分数不确定性对激光频率是在10 7±5份。准确确定远红外激光器发射的频率是非常关键的,因为它们经常被用来作为对其他测量值的参考,如在高采用激光磁共振自由基 – 分辨率光谱调查。作为该调查,二氟甲烷,CH 2 F 2的一部分,用作远红外线的激光介质。在所有八远红外激光的频率进行测定,第一次用频率范围从0.359至1.273的THz。这三个激光排放此调查期间被发现和报告与他们的最佳操作压力,偏振相对于CO 2的</suB>泵浦激光器和力量。
首先由HÖCKER执行的远红外激光频率的测量和同事在1967年他们测量的频率用于从直接放电氰化氢激光的311和337微米的排放量与微波信号的高次谐波将它们混合在硅二极管1。为了测量更高的频率,链激光器和谐波混频装置用于产生激光谐波2。最终2稳定化的二氧化碳(CO 2)激光器被选择,以合成所需的差频率3,4。今天,远红外线激光频率可达4太赫兹可以使用由两个产生的差频的只有第一谐波这种技术来测量稳定化的 CO 2参考激光器。更高频率的激光辐射也可以使用二次谐波测定,如由甲醇同位素异冠心病2 9 赫兹激光排放OH和CH 3 </sUB> 18 OH 5,6多年来,激光频率的精确测量已经影响了一些科学实验7,8和允许通过的电表由度量衡在巴黎大会一个新的定义, 1983年9 – 11
外差技术,如所描述的那些,已经在由光泵分子激光器产生的远红外激光频率测量也是很有好处的。由于光泵分子激光器由Chang和桥12的发现,千光泵远红外激光排放已产生与多种激光媒体。例如,二氟甲烷(CH 2 F 2)和其同位素产生超过250激光辐射时光学地由CO 2激光器泵浦。它们的波长范围是从大约95.6至1714.1微米13 – </s达> 15近75%,这些激光排放有其频率测量,而一些已光谱分配16 – 18。
这些激光器,和它们的精确测量的频率,已经于高分辨率光谱的进步起到了至关重要的作用。它们提供的激光气体的红外光谱研究的重要信息。通常,这些激光频率被用来验证红外和远红外光谱的分析,因为它们提供的激发振动状态的水平,往往从吸 收光谱19直接难以接近之间的连接。它们也可以作为初级辐射来源的研究调查过性,短命的自由基与激光磁共振技术20。有了这个极其敏感的技术,在顺磁性原子,分子转动和振转塞曼光谱和分子离子可以是Recorded而且随着调查用来创建这些自由基的反应率的能力进行分析。
在这项工作中,一个光泵浦分子激光, 如图 1所示,已被用来产生从二氟甲烷远红外激光辐射。这个系统包括一个连续波(CW) 的 CO 2激光器的泵和一个远红外激光腔。的反射镜内部的远红外激光腔重定向的 CO 2激光辐射向下抛光铜管,在经过26反射终止于所述腔的端部,散射任何剩余泵辐射之前。因此,远红外激光介质是使用横向泵送几何激发。产生激光的动作,若干变量被调节,同时一些,和所有随后的优化一次激光辐射是观察。
在该实验中,远红外激光辐射由金属INSU监视荡器 – 金属(MIM)点接触型二极管检测器。自1969年以来21所述的MIM二极管检测器已用于激光频率测量– 23在激光频率的测量,所述MIM二极管检测器之间的两个或更多个辐射源入射到二极管谐波混频器。所述MIM二极管探测器由一个削尖的钨丝接触经过光学研磨的镍基24。镍基体具有天然存在的薄氧化物层,其在绝缘层。
27以下最初在文献中记载的方法–一次激光发射检测,它的波长,偏振,强度和优化的操作压力,而其频率使用三激光外差技术25测定的记录。 4. 图2显示了光泵浦激光分子与具有独立的频率站两个附加连续波CO 2激光器参考bilization系统,利用在4.3微米的荧光信号的兰姆凹陷来自外部,低压参考单元28。这个手稿概述用于搜索远红外激光排放以及推定方法其波长和准确地确定它们的频率的过程。关于三激光外差技术细节以及各种部件和系统的运行参数可以在补充表A中一起引用4,25-27,29和30。
有迹象表明,需要一些额外的讨论中的协议中的几个关键步骤。当测量的远红外激光波长,如在步骤2.5.3概述的,它保证了远红外激光器发射的正在使用相同的模式是重要的。 (即TEM 00,TEM 01,等)可在激光腔中产生一个远红外激光波长的多种模式,从而以识别所使用的适当的相邻的腔模以测量波长13,29是很重要的, 41。以协助消除高阶模式,虹膜包括在每…
The authors have nothing to disclose.
This work was supported in part by the Washington Space Grant Consortium under Award NNX10AK64H.
Vacuum pump | Leybold | Trivac D4A | HE-175 oil; Quantity = 3 |
Vacuum pump | Leybold | Trivac D8B or D16B | Fomblin Fluid; Quantity = 1 of each |
Vacuum pump | Leybold | Trivac D25B | HE-175 oil; Quantity = 1 |
Optical chopper with controller | Stanford Research Systems | SR540 | |
Lock-in amplifier | Stanford Research Systems | SR830 | |
Spectrum analyzer | Agilent | E4407B | ESA-E Series, 9 kHz to 26.5 GHz Spectrum Analyzer |
Amplifier | Miteq | AFS-44 | Provides amplification of signals between 2 and 18 GHz. The amplifier is powered by a Hewlett Packard triple output DC power supply, model E3630A. |
Amplifier | Avantek | AWL-1200B | Provides amplification of signals less than 1.2 GHz. |
Power supply | Hewlett Packard | E3630A | Low voltage DC power supply for amplifier. |
Power supply | Glassman | KL Series | High voltage power supply for the CO2 lasers; Quantity = 2; negative polarity |
Power supply | Fluke | 412B | High voltage power supply used with the NIST Asymmetric HV Amp |
Detector | Judson Infrared Inc | J10D | For fluorescence cell; Quantity = 2 |
CO2 laser spectrum analyzer | Optical Engineering | 16-A | Currently sold by Macken Instruments Inc. |
Thermal imaging plates with UV light | Optical Engineering | Primarily used for aligning the CO2 reference lasers. Currently sold by Macken Instruments Inc. | |
Resistors | Ohmite | L225J100K | 100 kW, 225 W. Between 4 to 6 resistors are used in each ballast system. Each CO2 laser has its own ballast system. Fans are used to cool the resistors. |
HV relay, SPDT | CII Technologies | H-17 | Quantity = 3; one for each CO2 laser |
Amplifier | Princeton Applied Research | PAR 113 | Used with fluorescence cell; Quantity = 2 |
Oscilloscope | Tektronix | 2235A | Similar models are also used; Quantity = 2 |
Oscilloscope/Differential amplifier | Tektronix | 7903 oscilloscope with 7A22 differential amplifier | |
Power meter with sensor | Coherent | 200 | For use below 10 W. This is the power meter shown in Figure 2. |
Power meter with sensor | Scientech, Inc | Vector S310 | For use below 30 W |
Multimeter | Fluke | 73III | Similar models are also used; Quantity = 3 |
Data acquisition | National Instruments | NI cDAQ 9174 chassis with NI 9223 input module | Uses LabVIEW software |
Simichrome polish | Happich GmbH | Polish for the Nickel base used in the MIM diode detector. Although the Nickel base can be used immediately after polishing, a 12 hour lead time is typically recommended. | |
Pressure gauge | Wallace and Tiernan | 61C-1D-0050 | Series 300; for CO2 laser; Quantity = 3 |
Pressure gauge with controller | Granville Phillips | Series 375 | For far-infrared laser |
Zirconium Oxide felt | Zircar Zirconia | ZYF felt | Used as a beam stop |
Zirconium Oxide board | Zircar Zirconia | ZYZ-3 board | Used as a beam stop; Quantity = 4 |
Teflon sheet | Scientific Commodities, Inc | BB96312-1248 | 1/32 inch thick; used for the far-infrared laser output window |
Polypropylene | C-Line sheet protectors | 61003 | used for the far-infrared laser output window |
Vacuum grease | Apiezon | ||
Power supply | Kepco | NTC 2000 | PZT power supply |
PZT tube | Morgan Advanced Materials | 1 inch length, 1 inch outer diameter, 0.062 inch thickness, reverse polarity (positive voltage on outside); Quantity = 3 | |
ZnSe (AR coated) | II-VI Inc | CO2 laser window (Quantity = 3), lens, and beam splitter (Quantity 3) | |
NaCl window | Edmond Optics | Quantity = 1 | |
CaF window | Edmond Optics | Quantity = 2 | |
Laser mirrors and gratings | Hyperfine, Inc | Gold-coated; includes positioning mirrors | |
Glass laser tubes and reference cells | Allen Scientific Glass | ||
MIM diode detector | Custom Microwave, Inc | ||
Outro | Other materials include magnetic bases, base plates, base clamps, XYZ translation stage, etc. |