We have developed a technique to perform optical two-dimensional Fourier-transform (2DFT) spectroscopy in a reflection geometry. Various reflection 2DFT spectra are obtained for an atomic vapor. The technique is useful for the cases where optical 2DFT spectroscopy cannot be performed in the transmission geometry.
Optical two-dimensional Fourier transform (2DFT) spectroscopy has been developed over the last decade as a powerful tool for studying a variety of physical systems, ranging from atoms to molecules to solids. This review covers our use of 2DFT spectroscopy to study exciton dynamics in semiconductor nanostructures. In quantum wells, 2DFT spectroscopy confirms the importance of many-body contributions to the coherent optical response and reveals nonradiative double-quantum and Raman coherences. For natural quantum dots, 2DFT spectroscopy enables ensemble measurements of the homogeneous linewidth, including the temperature and density dependence. Relaxation from quantum well states into the quantum dots can also be studied using 2DFT spectroscopy.
Optical two-dimensional Fourier-transform (2DFT) spectroscopy is used to study the coherent optical response of potassium vapor in a thin transmission cell. Rephasing and nonrephasing spectra of the D1 and D2 transitions are obtained and compared to numerical simulations. Non-perturbative calculations using the optical Bloch equations give very good agreement with the experimental peak strengths and line shapes. Nonradiative Raman-like coherences are isolated using a different 2DFT projection. Comparison between the optical and Raman linewidths shows that dephasing is due to partially correlated energy fluctuations. Density-dependent measurements show distortion of 2DFT spectra due to pulse propagation effects.