【作者】 杨振；

【导师】 徐德刚；

【作者基本信息】 天津大学 ， 光电子与光子学技术， 2017， 硕士

【摘要】 太赫兹（Terahertz）波,又称为远红外波或亚毫米波,处于红外波段和微波波段之间。这个频率范围中的电磁波具有许多独特的性质,在成像、无损检测、通信、国防安全和环境检测等领域有着广阔的应用前景。作为产生太赫兹波的光学方法之一,基于非线性晶体受激电磁耦子散射的太赫兹参量振荡源具有很多优点,如室温运转、小型化、高峰值功率、时间和空间相干性好、可连续调谐等,近年来世界范围内的学者做了大量工作。然而,现有的太赫兹参量振荡源的主要问题依旧是输出功率和转化效率较低,其输出频率也不能覆盖整个THz波段。本文先针对高能量、快速调谐这两个方向研究,设计了环形腔浅表面垂直出射结构的太赫兹参量振荡源,实现了高能量快速调谐的太赫兹波输出,同时对这种新型结构的输出特性进行了分析,并与传统的平行平面腔结构结果做了对比;其次研究了宽调谐范围的太赫兹参量振荡源,利用环形腔结构的精确调谐和高能量输出特点,得到了基于KTiOPO₄（KTP）晶体的环形腔结构太赫兹参量振荡器中的精确输出特性,拓宽了基于KTP晶体的太赫兹参量振荡器的调谐范围,并用理论解释了在KTP晶体中不连续的调谐现象和双波长输出特性的原因。本文主要工作如下:1.研究了基于环形腔浅表面垂直出射结构的太赫兹波参量振荡器。通过借鉴罗兰圆环形腔结构和浅表面垂直出射结构,将环形腔的小型化快速调谐特性和表面出射结构的高光束质量高耦合效率特性相结合,解决了快速调谐中出射点漂移和硅棱镜耦合对光束质量影响较大的问题,实现了高能量（12.9μJ/pulse）和快速调谐（600μs/THz）的太赫兹波输出,这个结果比日本报道的基于条状铌酸锂晶体的环形腔结构输出脉冲能量高三个量级。同时,我们对这种新型结构的各项参数进行了分析。和使用相同泵浦源相同晶体的平行平面腔结构太赫兹参量振荡源的输出结果进行对比,环形腔结构拥有更高能量的太赫兹波能量输出和更低的泵浦能量损耗,这代表着环形腔结构拥有更高的光子转换效率。2.研究了宽调谐范围的太赫兹参量振荡源。通过将环形腔结构和KTP晶体相结合,利用环形腔结构的快速精确调谐和高功率输出特性得到了基于KTP晶体的太赫兹参量振荡源的宽调谐范围太赫兹波输出,拓宽了现有太赫兹参量振荡源的调谐范围,THz波输出频率范围为0.96-7.01THz。其调谐范围并不是在整个范围内连续,而是在0.96-1.87 THz,3.04-3.33 THz,4.17-4.48 THz,4.78-4.97 THz,5.125-5.168 THz,5.44-5.97 THz和6.74-7.01 THz这7个范围里分段连续。我们还使用色散理论成功解释了KTP晶体中的不连续的调谐现象的和双斯托克斯波长同时谐振的这两种现象,并且理论分析结果和实验结果几乎一致。在泵浦能量为210m J时,我们在5.7THz时得到5.47μJ/pulse的THz波输出,对应的能量转化效率为2.61×10^-5。更多还原

【Abstract】 THz（Terahertz）wave,also known as far-infrared wave or sub-millimeter wave,located at the boundary between the microwave and optical bands.It has many pretty properties,and is now regarded as a popular subject which can be applied in imaging,nondestructive testing,communications,national defense and security,environment monitoring.As one of the optical methods for the generation of terahertz waves,terahertz parametric oscillators based on the stimulated polariton scattering in nonlinear crystal have many advantages,such as room temperature operation,compactness,high peak power,good temporal and spatial coherence,continuous tunability,and the scholars around the world have done a lot of works in recent years.However,the main problem of existed terahertz oscillators is the low output power and conversion efficiency.In this paper,a surface-emitted ring cavity terahertz parametric oscillator is designed for the high-energy and fast-tuned terahertz output.At the same time,the output characteristics of this new structure are analyzed and it is compared with the results of the traditional cavity terahertz parametric oscillator.Due to the accurate tuning and the high energy output characteristics of the ring cavity terahertz parametric oscillator,the accurate output characteristics of the KTiOPO4（KTP）crystal in the terahertz parametric oscillator are obtained,and the tunable range of terahertz parametric oscillator based on the KTP crystal is widened.The reason for the discontinuous tuning range and dual-wavelengths output characteristics in KTP crystal is explained theoretically.The main work of this paper is as follows:1.A terahertz-wave parametric oscillator based on the surface-emitted ring-cavity configuration was designed to realize the high-energy（12.9μJ/pulse）and fast tuning（600μs/THz）THz wave output.The output energy is 1000 times larger than the results of the similar ring-cavity configuration reported in Japan,we get the high beam quality and high pulse energy THz wave output.At the same time,the parameters of the new structure are analyzed.By comparing the output energy of the THz oscillators with the same crystal structure of the same pump source,the ring cavity structure has higher energy THz energy output and lower pump energy loss,which means that the ring The cavity structure has a higher photon conversion efficiency.2.In order to broaden the tunable range of the terahertz parametric oscillator,we design a ring-cavity terahertz wave parametric oscillator with a KTP crystal,and a wide tuning range of 0.96-7.01THz was obtained.The tuning range was observed intermittently from 0.96-1.87 THz,from 3.04-3.33 THz,from 4.17-4.48 THz,from4.78-4.97 THz,from 5.125-5.168 THz,from 5.44-5.97 THz and from 6.74-7.01 THz.The dual-Stokes wavelengths resonance phenomena were observed in some certain tuning angle ranges.Through the theoretical analysis of the dispersion curve in KTP crystal,the intermittent THz wave tuning range and dual-wavelength Stokes waves operation during angle tuning process were explained.And the theoretical analysis was in good agreement with the experiment results.The maximum terahertz output energy was 5.47μJ at 5.7 THz under the pump energy of 210 mJ,corresponding to the maximum THz wave conversion efficiency of 2.61×10^-5.更多还原