We present multidimensional coherent spectroscopy that utilizes frequency combs and multi-heterodyne detection. We demonstrate its capability to measure collective hyperfine resonances in atomic vapor induced by long-range dipole-dipole interactions.
Abstract Optical multidimensional coherent spectroscopy provides information about the structure and excitation dynamics in a broad range of material systems. This book focuses on systems of interest in physics, including atomic vapors, semiconductor nanostructures and two-dimensional materials. An introduction to ultrafast spectroscopy and the fundamental concepts of multidimensional coherent spectroscopy applies to all material systems. Relevant experimental implementations, including phase-stabilized crossed-beams, frequency-tagged fully-collinear, three-dimensional and frequency-comb based methods. The use of the method to study atomic vapors, semiconductor quantum wells, semiconductor quantum dots and two-dimensional materials are described in separate chapters. The final chapters survey the use of the method in some other areas and speculate on future directions.
In recent years, frequency-comb-based multidimensional coherent spectroscopy has emerged as a very powerful optical method for studying samples with long dephasing times. It enables the measurement of comb resolution multidimensional coherent spectra in seconds as opposed to hours or even days required by traditional mechanical stage-based spectrometers. However, for some samples (e.g., cold atoms and molecules) the dephasing times could be longer than the repetition periods of the excitation lasers which means that the generated signal will not fully decay between the pulses. Depending on the relative phase or time between the pulses, the signals generated by the subsequent laser pulses can constructively or destructively interfere with each other. In this paper we study this behavior by solving the optical Bloch equations and provide a theoretical description of frequency-comb-based multidimensional coherent spectroscopy.