Abstract

Non-linear spectroscopy has been an important tool for revealing the dynamics in condensed matter systems for decades. Two-dimensional Fourier transform spectroscopy (2DFTS) is such a technique that has recently been extended from nmr to optical spectroscopy and is becoming increasingly important for revealing the dynamics of quantum mechanical coupling between different electronic states. In standard 2DFTS a transient four-wave mixing signal is detected by spectral interfereometry, which allows determination of both the intensity and phase as a function of emission energy. However, this approach requires phase stability between each of the three pulses generating the FWM signal and a fourth local oscillator pulse, which is challenging, and prevents the use of two-colour excitation. We have developed a technique that is able to retrieve the phase of the emission from spectrally resolved intensity measurements, thereby removing the need for interferometry, simplifying the experimental setup, and allowing the possibility of two-colour excitation.

I will be discussing the development of this technique, including the experimental fundamentals, and the phase retrieval teqhniques that are drawn from other areas of physics including coherent diffractive imaging and frequency resolved optical gating (FROG) measurements. I will also discuss the significance and interpretation of 2DFTS, and the exciting applications of the technique in the past, present and future.