Construction of Ultrashort Pulse Lasers and Spectroscopy System in UV and Blue Light Regions for the Study of New Semiconductor Superlattices

本研究项目的目标是建立一个在紫外和蓝光区域工作的超短脉冲激光系统。本项目还包括皮秒时间分辨光谱系统的开发，以评估新的半导体超晶格在超短脉冲激光激励下的动态响应。1988-1991年这三年所取得的成果总结如下：我们开发了一个皮秒紫外和蓝区激光系统，该系统由锁模YAG激光器的三次和四次谐波产生。利用KTP和β - bab_2o_4的非线性光学晶体和专门设计的光学系统，实现了基波红外激光的转换。通过皮秒YAG激光器同步泵浦的染料激光器皮秒脉冲的二次谐波转换，获得了可调谐的紫外皮秒光源。由于特殊设计的光学元件和非线性光学晶体具有良好的相位匹配条件，使其对紫外光和蓝光的转换效率更高。在傅里叶极限条件下，设计了一种用于皮秒区域时间分辨光谱的三重单色仪。为此，在第一个双单色化阶段采用减色散结构，使我们的时间分辨率达到10 ps，光谱分辨率为2-3 cm^<-1>。该光谱仪具有第三个单色化阶段，用于高光谱分辨率测量，带有多通道探测器。通过构建该光谱仪，实现了高时间分辨率和高光谱分辨率的测量系统。利用超快时间分辨光谱系统研究了热壁外延、MOCVD和MBE生长的Cd_<1-x>Mn_xTe和ZuTe-ZuSe超晶格的激子动力学。Cd_<1-x>Mn_xTe的超晶格表现出量子阱中激子磁极化子的快速弛豫过程，而ZnTe-ZnSe的超晶格表现出电子和空穴分别在ZnSe和ZnTe层中分离的ii型量子阱结构中的激子动力学。结果表明，时间分辨光谱系统对新型宽带隙半导体超晶格的表征和开发是非常有用的。少

The objective of this research project is the construction of an ultrashort pulse laser system which is operating in ultraviolet and blue light regions. This project also includes the development of the picosecond time resolved spectroscopy system to evaluate the dynamical response of new semiconductor superlattices by exciting with the ultrashort pulse lasers. The obtained results in these three years (1988-1991) are summarized as follows :1. We have developed a picosecond laser system in uv and blue region, which is operating by 3rd and 4th harmonic generation of a mode locked YAG laser. The conversion of the fundamental ir laser light has been performed by using non-linear optical crystals of KTP and beta-BaB_2O_4 with specially designed optical system. Tunable uv picosecond-light source is also attained by 2nd-harmonic conversion of picosecond pulses of a dye-laser which is synchronously pumped by the picosecond YAG laser. The efficiency of the conversion to uv and blue lignt is re … More asonably high which is due to the specially designed optics and also due to attainment of the good phase-matching condition for the nonlinear optical crystals.2. A triple monochrometor is designed to achieve the time resolved spectroscopy in picosecond region with the Fourie limit condition. For that purpose subtract-dispersion confiuration is adopted for the first doubly-monochromating stage, which enables us 10 ps time resolution with spectaral resolution of 2-3 cm^<-1>. The spectrometer has third monochromating stage for high-spectral-resolution measurement with a multichannel detector. By constructing this spectrometer we have attained the measurement system with both high-time and high-spectral resolutions.3. By using the ultrafast time-resolved spectroscopy system we have studied the exciton dynamics of the superlattices of Cd_<1-x>Mn_xTe and ZuTe-ZuSe, which are grown by hot-wall-epitaxy and MOCVD and MBE. The superlattices of Cd_<1-x>Mn_xTe show very fast relaxation process of excitonic magnetic polarons in quantum wells while the ZnTe-ZnSe superlattices display dynamics of excitons in a type-II quantum well structure where the electrons and holes are separated in the ZnSe and ZnTe layers respectively. From the results it is verified that the present time resolved spectroscopy system is very useful for the characterization and development of the new semiconductor superlattices with wide band gaps. Less