Ultrafast dynamics study of condensed-phase materials using Raman and transient grating method.

摘要

This thesis work is composed of four chapters covering the understanding of ultrafast dynamics of certain condensed-phase materials using contemporary laser techniques.; Chapter I is an introductory chapter that briefly outlines the structure of the whole thesis, while highlighting the most important contents in the upcoming chapters of the thesis.; A Raman study of anthracene under high pressures in a diamond anvil cell is given in Chapter II. In this chapter, important experimental details about the diamond anvil cell are described. Raman data of anthracene under high pressure excited by conventional continuous wave laser are presented and their relevance to laser initiated shock wave studies are discussed.; In Chapter III, non-linear picosecond laser techniques are utilized to study surface acoustic waves on the surfaces of opaque materials, under both ambient conditions and high pressures. A pump-probe transient grating method is used. Surface acoustic waves that oscillate on a nanosecond time scale are studied on different crystal surfaces. The acoustic wave velocities measured can be used to obtain the elastic properties of these materials. High-pressure measurement of surface acoustic modes of polycrystalline Al in a diamond anvil cell is presented as well. The high-pressure impulsive stimulated scattering represents a new way to probe the elastic properties of materials under extreme pressure and temperature conditions.; In Chapter IV, a tunable chirped-pulse amplified femtosecond laser system is used in the transient grating study of polycyclic aromatic hydrocarbon (PAH) radical cations in a boric acid matrix. The excited state dynamics of PAH radical cations are believed to be important as PAH radical cations are involved in stellar evolution, carcinogenic process as well as some fundamental redox reactions. PAH radical cations are excited by femtosecond laser pulses, and their ground-state recovery lifetimes are studied.; The state-of-the-art laser system used in Chapter IV is described in more detail in the Appendix, where the working theory and pictures of the major components are presented.