Application of multi-colour femtosecond pulses towards light-matter interactions

Abstract

Multi-colour femtosecond laser fields provide significant benefits when probing states of matter, through either increasing the resolution of transient spectroscopy or via optimisation of highly nonlinear processes. In this thesis, I present several experimental advancements in the development and application of such laser fields towards novel organic photovoltaic devices and optimisation of high-harmonic generation (HHG). In the first case, using sub-10 fs two-coloured fields in a comparative study between traditional pump-probe techniques and pump-push photocurrent (PPPC), we showed that PPPC was able to more readily distinguish the bound states of an optically-excited system, paving the way for new devices to be studied and understood. The experimental system is poised to explore other less-understood molecular processes in the near future, such as quantum beating. For the second, we developed and characterised a three-colour femtosecond field synthesizer with the goal of generating an approximated ‘perfect waveform’ for HHG. We combined a 350 μJ, 6.3 fs near infrared pulse with its second harmonic (40 μJ, 46 fs) and a third, 50 μJ, 41 fs, short-wave infrared field, at 1300 nm. Some technical challenges remain, such as the phase instabilities of the longer-wavelength field. However, we have demonstrated that, by using two of the three channels, a significant enhancement to the flux of isolated attosecond pulses generated by HHG can be achieved without sacrificing the duration of the attosecond pulse.