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Research on Coherent Tunable Terahertz Source by using Nonlinear Optical Effect

利用非线性光学效应的相干可调谐太赫兹光源研究

基本信息

批准号：
08455028
负责人：
TANIUCHI Tetsuo
金额：
$ 4.74万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

We have investigated a continuously tunable THz-wave generation by using an optical parametric oscillation (OPO) in LiNbO_3 pumped by a Q-switched Nd : YAG laser. The process involved is the OPO by stimulated polariton scattering from the soft phonon mode of A_1-symmetry in LiNbO_3. As noncollinear phase matching condition is satisfied, a widely tunable THz-wave can be obtained by slightly changing the angle between pump and Stokes wavevectors. We proposed a new coupling method such as a monolithic grating coupler and a prism coupler onto a LiNbO_3 crystal. By introducing the prism coupler, we found that the change the radiation angle of THz-wave is only 0.03ﾟ for Si prism coupler, providing this method to be far more convenient than the conventional angled surface coupler. The measured output power of THz-wave was 3mW when pumping energy of Nd : YAG laser was 34.5mJ,and an efficient tunable THz-wave radiation was obtained in the range of 140-310 mu m (0.97-2.15THz).We also experimentally studied cryogenic characteristics of THz-wave generation. As the temperature decreased to 78K,the absorption coefficient alpha was reduced from 30.6cm^<-1> to 6.9cm^<-1> at 1.6THz. We obtained 125 times higher THz-wave output and the threshold was reduced by 32% at 78K,compared to that obtained at room temperature.This THz-wave source has significand advantages in compactness, tunability and case of handling. It can be expected to play an important role in many applications such as ranging, imaging and spectroscopy in THz-wave region. We have applied the THz-wave radiation to the absorption spectroscopy of water vapor by using 1m Iong metal hollow tube and demonstrated for the first time that differential imaging between two wavelengths emphasized the image of a tagged object with an absorption coefficient dependent on THz wavelength.

研究了用调Q Nd：YAG激光泵浦LiNbO_3晶体产生连续可调谐太赫兹波的光参量振荡（OPO）。所涉及的过程是LiNbO_3中A_1对称软声子模的受激极化激元散射OPO。当满足非共线相位匹配条件时，只要改变抽运波矢与斯托克斯波矢的夹角，就可以得到宽调谐的太赫兹波。本文提出了一种新的耦合方法，如单片光栅耦合器和棱镜耦合器到LiNbO_3晶体上。通过引入棱镜耦合器，我们发现硅棱镜耦合器对太赫兹波辐射角的改变仅为0.03 μ m，比传统的角面耦合器方便得多。在泵浦能量为34.5mJ的Nd：YAG激光器中，测得THz波输出功率为3 mW，在140-310 μ m（0.97-2.15THz）范围内获得了有效的可调谐THz波辐射，并对THz波产生的低温特性进行了实验研究。当温度降低到78 K时，在1.6THz处的吸收系数α从30.6cm^3降低<-1>到6.9cm^3<-1>。在78 K下获得了比室温下高125倍的太赫兹波输出，阈值降低了32%，该太赫兹波源在结构紧凑、可调谐性和使用方便等方面具有明显的优势。它在太赫兹波段的测距、成像和光谱学等方面有着重要的应用前景。利用1 m长的金属空心管将太赫兹波辐射应用于水蒸气的吸收光谱，首次证明了两个波长之间的差分成像增强了吸收系数依赖于太赫兹波长的标记物的图像。