Mehdi Mohammad Kazemi

• Nonlinear optical effects are known and investigated for several decades. Since the first observation of these phenomena, a great number of applications have been found for them in science and technology. The combination of nonlinear optical effects with ultra-short laser pulses has advanced the field of spectroscopy and now allows for studying and even controlling the elementary dynamics of molecular systems on a picosecond, femtosecond, and even attosecond time scale. In the first part of this PhD thesis, femtosecond laser pulses are used to generate second-order nonlinear optical effects. By controlling the phase relation between these second order phenomena, an all-optical ultrafast Toffoli logic gate is implemented. The proposed simple technique is a proof of principle, which can be a step towards ultrafast switching and optical computation. The second part of the thesis focuses on the application of the four-wave mixing (FWM) process, a third-order nonlinear effect, for the investigation of the vibrational dynamics of molecular systems. Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) is applied to probe the ultrafast coupling of vibrational modes in ionic liquids. Specifically, the effect of the alkyl chain length and anion substitution on the vibrational dynamics of fingerprint and C-H stretching modes in ionic liquids are investigated. This study provides a better insight into the intermolecular interactions in ionic liquids, which can be used to optimize the design of task-specific materials.