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

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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