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arXiv · 2607.03469

Photo-thermal 2D spectroscopy: a different type of action

Pavel Malý·Xiaoji G. Xu·Tomáš Mančal
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Abstract

Advances in multidimensional spectroscopy have seen the rise of action detection, where coherent response is encoded into incoherent signals. These are typically proportional to the excited-state population, an example in 2D electronic spectroscopy (2DES) is fluorescence-detected 2DES (F-2DES), and in 2D infrared (2DIR) tag-loss 2DIR (TL-2DIR). Very recently, a new type of photo-thermal action signal has been introduced in 2DIR, detecting the generated heat by atomic force microscopy-based 2DIR (AFM-2DIR). We present a unified theoretical framework for population- and heat-based 2D spectroscopy, highlighting their complementary features. In the infrared, TL-2DIR reflects the system linear response, whereas AFM-2DIR produces spectra resembling conventional 2DIR, with sensitivity to anharmonicity and mode coupling. Our model reproduces key experimental AFM-2DIR features, confirming measurement in a highly nonlinear regime. Extending photothermal detection to electronic spectroscopy, we compare F-2DES with proposed photo-thermal 2DES (PT-2DES). PT-2DES closely resembles conventional 2DES, while enjoying the advantages of action detection.

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Pavel Malý, Xiaoji G. Xu, Tomáš Mančal. 2026-07-03. Photo-thermal 2D spectroscopy: a different type of action. https://arxiv.org/abs/2607.03469

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