Development of Frequency Domain Multidimensional Spectroscopy with Applications in Semiconductor Photophysics

Book excerpt: Coherent multidimensional spectroscopy (CMDS) encompasses a family of experimental strategies involving the nonlinear interaction between electric fields and a material under investigation. This approach has several unique capabilities: (1) resolving congested states, (2) extracting spectra that would otherwise be selection-rule disallowed, (3) resolving fully coherent dynamics, (4) measuring coupling, and (5) resolving ultrafast dynamics. CMDS can be collected in the frequency or the time domain, and each approach has advantages and disadvantages. Frequency domain ``Multi-resonant'' CMDS (MR-CMDS) requires pulsed ultrafast light sources with tunable output frequencies. These pulses are directed into a material under investigation. The pulses interact with the material, and due to the specific interference between the multiple fields the material is driven to emit a new pulse: the MR-CMDS signal. This signal may have a different frequency and/or direction than the input pulses, depending on the exact experiment being performed. The MR-CMDS experiment involves tracking the intensity of this output signal as a function of different properties of the excitation pulses. These properties include (1) frequency. (2) relative arrival time and separation (delay), (3) fluence, and (4) polarization, among others. Thus MR-CMDS can be thought of as a multidimensional experimental space, where experiments typically involve explorations in one to four of the properties above. Because MR-CMDS is a family of related-but-separate experiments, each of them a multidimensional space, there are special challenges that must be addressed when designing a general-purpose MR-CMDS instrument. These issues require development of software, hardware, and theory. Part I: Background introduces relevant literature which informs on this development work. Part II: Development presents five strategies used to improve MR-CMDS: (1) processing software, (2) acquisition software (3), active artifact correction, (4) automated OPA calibration, and (5) finite pulse accountancy. Finally, Part III: Applications presents four examples where these instruments, with these improvements, have been used to address chemical questions in semiconductor systems.