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

本研究计画的目标是建构一套可在紫外及蓝光区运作的超短脉冲雷射系统。本计画亦包括发展皮秒时间分辨光谱系统，以评估超短脉冲雷射激发下新型半导体超晶格的动态响应。1988-1991年三年来的研究结果如下：1.利用YAG锁模激光器的三次和四次谐波产生，研制了紫外和蓝光皮秒激光系统。采用KTP和β-BaB_2 O_4非线性光学晶体，配合特殊设计的光学系统，实现了红外激光的基频转换。利用皮秒YAG激光器同步泵浦染料激光器，将染料激光器的皮秒脉冲进行二次谐波转换，得到了可调谐的皮秒紫外光源。转换成紫外光和蓝光的效率是很高的 ...更多信息 合理的高，这是由于特殊设计的光学器件，也是由于非线性光学晶体达到了良好的相位匹配条件.设计了一台三重单色器，实现了在傅里叶极限条件下的皮秒时间分辨光谱。为此，第一级双单色器采用减色散配置，这使得我们能够获得10 ps的时间分辨率和2-3 cm-2的光谱分辨率<-1>。该光谱仪具有第三单色级，用于使用多通道检测器进行高光谱分辨率测量。通过搭建该谱仪，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<1-x>热壁外延、MOCVD和MBE生长的Cd_ Mn_xTe和ZuTe-ZuSe超晶格的激子动力学。Cd_<1-x>Mn_xTe超晶格在量子威尔斯阱中表现出激子磁极化子的快速弛豫过程，而ZnTe-ZnSe超晶格在ZnSe和ZnTe层中分别表现出电子和空穴分离的II型量子阱结构中的激子动力学过程。实验结果表明，该时间分辨光谱系统对研究和开发新的宽禁带半导体超晶格是非常有用的。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