The investigation of resveratrol with conventional and ultrafast pump-probe spectroscopy techniques
Thesis (MSc (Physics))--University of Stellenbosch, 2009.
An ultrafast pump-probe spectroscopy experiment was developed in order to investigate the fast photoinduced isomerization reaction of the molecule resveratrol. Characteristics of the resveratrol molecule are discussed, including the photoisomerization reaction from trans- to cis-resveratrol. The experimental setup for the conventional spectroscopy measurement was developed and characterized in order to investigate and understand the conventional absorption and uorescence spectroscopy of resveratrol thoroughly. The absorption spectra for both trans- and cis-resveratrol, as well as the uorescence spectra were measured, discussed and explained. This therefore forms a foundation and serves as an initial step to develop a pump-probe spectroscopy experiment for resveratrol. A general overview of ultrafast pump-probe spectroscopy is presented, as well as an explanation of the nal developed experimental setup. The principles and characteristics of the chirped pulse ampli cation (CPA) femtosecond laser source and the tunable noncollinear optical parametric ampli er (NOPA) employed as the pump pulse are discussed. The process of white light continuum (WLC) generation was investigated to utilize as the ultrashort probe pulse. Two white light continuum generation experimental setups were developed and characterized for WLC generation in a transparent medium with the fundamental CPA laser light at 775 nm (in sapphire) and with the second harmonic (SH) of the CPA light at 387 nm (in quartz). A spectrometer was designed, built and characterized in conjuction with a line focus, for simultaneous measurement of the absorption in the pumped, unpumped and reference regions in the sample. In this way the photoisomerization of resveratrol could be measured with temporal resolution as a transient absorption signal. A 420 μg/ml resveratrol solution in ethanol was investigated in this pump-probe spectroscopy experiment and the results obtained are discussed accordingly.