Work

Background-free measurement of exciton–exciton annihilation by two-quantum fluorescence-detected pump–probe spectroscopy

Year: 2026

Type: article

Abstract: We introduce two-quantum (2Q) fluorescence-detected pump-probe (F-PP) spectroscopy as a tool to probe ultrafast multiparticle interactions in many-body systems. We describe a pulse-shaper-based fully collinear setup utilizing phase cycling to capture the 2Q F-PP signal simultaneously with the one-quantum (1Q) F-PP signal. Thus, we investigate the dynamics of energy transfer and diffusion-limited annihilation. We apply a data post-processing strategy to isolate excited-state dynamics from spurious background. The technique is applied to a squaraine heterodimer and a squaraine copolymer to demonstrate the removal of so-called incoherent mixing that generally plagues action-detected nonlinear spectroscopy on multichromophoric systems. In particular, we show that this approach is not only applicable to 1Q but also to 2Q F-PP signals, eliminating incoherent mixing contributions as well as other "parasitic" signals that result from pulse-overlap ambiguities. As a result, we retrieve background-free spectral and dynamical information of doubly excited electronic states.

Source: The Journal of Chemical Physics

DOI: 10.1063/5.0305911

Authors: Ajay Jayachandran, Stefan Mueller, Christoph Lambert, Tobias Brixner

Institution: University of Würzburg

Language: English

Topic: Spectroscopy and Quantum Chemical Studies

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: green

Funders: European Research Council, HORIZON EUROPE European Research Council

Awards: G2458472030, Isolating Many-Particle Correlations in Time and Space