【作者】 张栋文；

【导师】 袁建民；

【作者基本信息】 国防科学技术大学 ， 物理学， 2008， 博士

【摘要】 太赫兹辐射源和太赫兹时域光谱,是太赫兹技术研究领域的两个重要方向。本文搭建了一套太赫兹时域光谱系统,结合密度泛函微扰理论研究了GaSe晶体的吸收光谱,并在GaSe晶体中光学差频产生窄带可调谐的太赫兹辐射。主要研究内容包括:1、搭建了一套太赫兹时域光谱系统。通过实验比较飞秒激光产生太赫兹辐射的多种方法,建立了一套基于ZnTe(110)晶体光整流产生和电光采样探测的太赫兹时域光谱系统,用1mm厚的ZnTe晶体产生和探测太赫兹辐射,通过几何优化,系统的信噪比大于1000,光谱范围为0.1-2.5THz,光谱分辨率50GHz,为研究样品在太赫兹波段的光学性质提供了一个很好的平台。2、实验验证了太赫兹时域光谱系统的优化方案。通过求解非线性耦合波方程分析了太赫兹辐射的波形,比较了群速失配对发射晶体和探测晶体的不同影响,在实验上验证用1mm厚ZnTe晶体产生太赫兹辐射,3.5mm厚ZnTe晶体探测太赫兹辐射,可以实现谱宽和灵敏度的最优组合。通过噪声分析,提出了电光采样的平衡正交探测模式,并实验证实在同样的条件下,使用平衡正交探测模式可以将信噪比提高2.5倍。3、研究了GaSe晶体在太赫兹波段的吸收结构。实验测量了室温下GaSe晶体的傅立叶变换红外吸收光谱,发现GaSe晶体在剩余射线带两侧存在很多吸收结构。测量了GaSe晶体在低温下的太赫兹时域光谱,通过密度泛函微扰理论计算的声子谱,指认了GaSe在太赫兹波段的吸收峰,并推断样品中含有堆叠缺陷。4、在GaSe晶体中差频产生窄线宽可调谐的太赫兹辐射。利用Nd:YAG激光器和窄线宽光参量振荡器,在GaSe晶体中共线相位匹配产生太赫兹辐射。通过构造长脉冲法,利用热辐射计在稳态的响应度,测量了太赫兹辐射脉冲能量。用傅立叶变换红外光谱仪的步进扫描功能测量了太赫兹辐射的频率。这套全固态太赫兹辐射源重复频率10Hz,在0.5-4.7THz范围内可调谐,在3THz频率的峰值功为17.3W,谱线宽度小于0.3cm-1,可用于太赫兹辐射高分辨光谱研究。5、和本文相关的其它研究。在太赫兹时域光谱的基础上,研究了透射式太赫兹扫描成像。在差频产生窄线宽可调谐的太赫兹辐射的过程中,研制了双波长光参量振荡器,并且差频产生了可调谐的红外线。更多还原

【Abstract】 Terahertz sources and terahertz time-domain spectra are two important fields interahertz technology and attract great interests of research in recent years. We have builtup a terahertz time-domain spectral system and use it to investigate the absorptionspectrum of GaSe crystals combined with the calculation of density-functionalperturbation theory. In addition, we have realized a tunable terahertz wave source with anarrow line-width by difference-frequency generation in GaSe crystals. The majorresults of this thesis are outlined as following:1、We have set up a terahertz time-domain spectral system. After extensiveexperimental comparison of many kinds of terahertz sources generated byfemtosecond laser, the terahertz time-domain spectral system is finally based onthe optical rectification and electro-optic sampling of ZnTe (110) crystal with thethickness of 1 mm. The geometrically optimized system is a good experimentalplatform for the study of optical properties of many samples in terahertz rangeswith a signal-to-noise ratio more than 1000, a spectral range in 0.1-2.5 THz and aspectral resolution about 50 GHz.2、We have validated the optimization of the terahertz time-domain spectral system.Firstly, terahertz waveforms were analyzed by solving nonlinearly coupled waveequations. The different influence of group-velocity mismatch on the ZnTeemitter and the sensor was pointed out and the optimal balance between bandwidth and sensitivity of the system was experimentally demonstrated using 1 mmthick ZnTe as an emitter and 3.5 mm thick ZnTe as a sensor. Secondly, thebalanced cross-polarization detection mode was proposed by the noise analysisof the system and the improvement of the signal-to-noise ratio wasexperimentally confirmed to 2.5 times higher in the same condition.3、We have investigated the absorption spectra of GaSe crystals in the terahertzrange. Abundant absorption structure beside the reststrahlen band of GaSecrystals was found when the FTIR absorption spectrum was measured in theroom temperature. The absorption peaks of GaSe crystals in the terahertz rangewere assigned by time-domain spectrum at low temperatures combined with thecalculation of density-functional perturbation theory and the stack faults in theGaSe sample were predicted.4、We have demonstrated the tunable, narrow line-width terahertz source based ondifference frequency mixing in GaSe. Employing an Nd:YAG laser and a narrowline-width OPO, the tunable terahertz radiation was realized by collinearphase-matching. The absolute pulse energy was measured with a bolometeraccording to its response to the stable radiation by constructing of a long terahertz pulse from its single response to a nanosecond terahertz pulse. Thefrequency of terahertz radiation is measured with a FTIR using the step-scanfunction. The all-solid terahertz source produces 17.3 W peak power at 3.07 THzat a repetition of 10 Hz in the tunable range of 0.5-4.7 THz with a line-width lessthan 0.3 cm-1 and has a potential application in high-resolution spectralinvestigations.5、We also carried out some work related to this thesis. The transmission scanterahertz imaging was introduced following the terahertz time-domain spectrum.The dual-wavelength OPO was developed and the tunable mid-infrared radiationwas obtained in the GaSe before the terahertz source was realized.更多还原