(英)适用于太赫兹空间传输的透镜设计及验证
投稿时间:2016-12-22  修订日期:2017-04-09  点此下载全文
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作者单位E-mail
杨秋杰 上海技术物理研究所 yqj488112gxx@163.com 
何志平 上海技术物理研究所 hzping@mail.sitp.ac.cn 
舒嵘 上海技术物理研究所 shurong@mail.sitp.ac.cn 
基金项目:国家杰出青年科学基金
中文摘要:太赫兹的空间自由传输是太赫兹领域的重要研究内容,而太赫兹波束准直是实现太赫兹空间自由传输的关键技术。与可见或近红外激光相比,太赫兹激光作为大角度发散的高斯波束不能简化为平面波或球面波,这导致其传输行为与可见或近红外激光相比有较大差异。经典电磁理论和ABCD法则的理论推导一致认为:正透镜实现太赫兹激光束的会聚,但不同于可见或近红外激光光束经正透镜会聚后其像距等于焦距这一理论,太赫兹波束经透镜会聚后其像距明显小于焦距;正透镜用于探测器之前可以提高太赫兹波束的能量利用率,但却不能显著的提高太赫兹波束的准直特性;焦距和太赫兹激光光束波前半径相匹配的负透镜更适用于太赫兹波束的准直,负透镜的设计参数应满足 ,其中 为太赫兹晶体到负透镜的距离, 为太赫兹激光的束腰直径, 为太赫兹激光的中心波长。通过实验证实, 的正透镜位于经典光学设计理论所认为的最佳位置时,即 ,太赫兹波束以2.5°的发散角在透镜后 的位置实现会聚; 的负透镜位于与太赫兹激光光束波前半径相匹配的位置时,即 ,太赫兹激光的发散角从6°提高到0.1°;太赫兹的20米传输实验中,负透镜准直探测方案比正透镜准直探测方案更加简单有效。这一理论发现,将对太赫兹的远距离传输产生重要的指导作用。
中文关键词:太赫兹,透镜,激光,传输
 
Lens design and verification used for terahertz space transmission
Abstract:Free space transmission is an important topic in terahertz technology research. Beam collimation is the key to free space transmission. Compared with visible and infrared lasers, the wave front of terahertz beams can be simplified to neither a plane nor spherical wave. It is a Gaussian beam with a big divergence angle. Theoretical derivation from the classical electromagnetic theory and ABCD laws makes a good agreement: firstly, the positive lens makes the terahertz beam converge in front of the focal plane which is quite different from that it makes the visible or infrared lasers converge on the focal plate; secondly, the positive lens used in front of the detector can improve the energy utilization ratio but does not substantially enhance the beam collimation; thirdly, the negative lens which is match with the radius of the Gaussian beam’s wave front is more appropriate for terahertz beam collimation. The parameter for negative lenses is determined by , where is the distance from terahertz crystal to the lens, is the beam waist and is the center wavelength of the terahertz beam. Experiments show that a negative lens with at the match place, , can improve the terahertz beam collimation from 6° to 0.1°, while a positive lens with at the best position, , which is determined by classical optic, only achieves beam convergence at with an angle of 2.5°. We obtain 20-m terahertz space transmission with a negative lens that has a very simple optical scheme. The signal obtained is seven times greater than that obtained with the positive lens scheme. This discovery will play an important role in free space transmission and terahertz imaging.
keywords:terahertz  lens  lasers  transmission
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