Fast phase cycling in non-collinear optical two-dimensional coherent spectroscopy*

The optical two-dimensional coherent spectroscopy (2DCS) has applications in different systems such as atomic vapors, semiconductor quantum wells, perovskites, and so on. The sensitivity of the detection is critical for increasing the signal to noise ratio in 2DCS. In addition to the desired nonlinear signal corresponding to the specific excitation pathway; there will be background signals, which arise from other excitation pathways, fluorescence, and non-resonance scatter of excitation laser beams. To eliminate this background, we developed a fast phase-cycling scheme in a non-collinear optical 2DCS by using liquid crystal phase retarders to modulate the phases of two excitation pulses [1]. We cancel out the background by adding and subtracting a series of interferograms measured with the proper phase configuration. We demonstrated the effectiveness of this method in optical 2DCS measurements of a potassium atomic vapor. This fast phase-cycling technique will broaden the scope of 2DCS applications.

[1] M.F. Munoz, A. Medina, T.M. Autry, G. Moody, M.E. Siemens, A.D. Bristow, S.T. Cundiff, and H. Li, Optics Letters 45, 5852 (2020).