Femtosecond optical spectroscopy and microscopy with phase coherent pulses

This dissertation focuses on femtosecond optical spectroscopy and microscopy by using ultrashort laser pulse shaping technology.; Collinear phase coherent two-dimensional spectroscopy on the organic dye Coumarin 102 was performed. The collinear phase coherent three-pulse sequences in the near infrared wavelength (800 nm) were generated by an acousto-optic pulse shaper. Coumarin 102 has a broad absorption band of around 400 nm. Two-photon absorption of the 800 nm light in Coumarin 102 is essential to perform the experiment. For comparison another set of experiments with the light frequency doubled to 400 nm was also performed. The results obtained show similar features with different details. The energy level information, e.g. linewidth, can be retrieved from the two-dimensional spectral peaks.; With pulse shaping technology the possibility to perform ultrafast laser microscopy aiming at potential biomedical application was also explored. The information utilized to differentiate chemicals is two-photon absorption and the structural information can also be retrieved from self-phase modulation. The nonlinear signal from these experiments is very small compared with input laser power. A heterodyne detection method was performed by creating a spectral hole in the laser spectrum with the pulse shaper. The signal generated is mixed with the local oscillator. The results from Rhodamine 6G, oxyHemoglobin and pheomelanin show the difference and imply promising further development with this method.; The last part of this dissertation is a previous work on a novel structure wavelength tunable semiconductor laser based on asymmetric twin waveguide technology. To integrate several optoelectronic devices together, several schemes are available. Asymmetric twin waveguide technology is the only integration platform which does not require material regrowth and quantum well intermixing. The tunable laser based on this technology can be used as a local oscillator in a coherent optical communication system and be integrated with other devices using the asymmetric twin waveguide platform.