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Proceedings Paper

Experimental validation of a theoretical model of dual wavelength photoacoustic (PA) excitation in fluorophores
Author(s): Julia Märk; Christoph Theiss; Franz-Josef Schmitt; Jan Laufer
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Paper Abstract

Fluorophores, such as exogenous dyes and genetically expressed proteins, exhibit radiative relaxation with long excited state lifetimes. This can be exploited for PA detection based on dual wavelength excitation using pump and probe wavelengths that coincide with the absorption and emission spectra, respectively. While the pump pulse raises the fluorophore to a long-lived excited state, simultaneous illumination with the probe pulse reduces the excited state lifetime due to stimulated emission (SE).This leads to a change in thermalized energy, and hence PA signal amplitude, compared to single wavelength illumination. By introducing a time delay between pump and probe pulses, the change in PA amplitude can be modulated. Since the effect is not observed in endogenous chromophores, it provides a contrast mechanism for the detection of fluorophores via PA difference imaging. In this study, a theoretical model of the PA signal generation in fluorophores was developed and experimentally validated. The model is based on a system of coupled rate equations, which describe the spatial and temporal changes in the population of the molecular energy levels of a fluorophore as a function of pump-probe energy and concentration. This allows the prediction of the thermalized energy distribution, and hence the time-resolved PA signal amplitude. The model was validated by comparing its predictions to PA signals measured in solutions of rhodamine 6G, a well-known laser dye, and Atto680, a NIR fluorophore.

Paper Details

Date Published: 11 March 2015
PDF: 10 pages
Proc. SPIE 9323, Photons Plus Ultrasound: Imaging and Sensing 2015, 93233G (11 March 2015); doi: 10.1117/12.2082613
Show Author Affiliations
Julia Märk, Technische Univ. Berlin (Germany)
Christoph Theiss, Technische Univ. Berlin (Germany)
Franz-Josef Schmitt, Technische Univ. Berlin (Germany)
Jan Laufer, Technische Univ. Berlin (Germany)
Charité Univ. Hospital (Germany)

Published in SPIE Proceedings Vol. 9323:
Photons Plus Ultrasound: Imaging and Sensing 2015
Alexander A. Oraevsky; Lihong V. Wang, Editor(s)

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