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Enhanced two-photon excited fluorescence from imaging agents using true thermal light


Two-photon excited fluorescence (TPEF) is a standard technique in modern microscopy1, but is still affected by photodamage to the probe. It has been proposed that TPEF can be enhanced using entangled photons2,3, but this has proven challenging. Recently, it was shown that some features of entangled photons can be mimicked with thermal light, which finds application in ghost imaging4, subwavelength lithography5 and metrology6. Here, we use true thermal light from a superluminescent diode to demonstrate TPEF that is enhanced compared to coherent light, using two common fluorophores and luminescent quantum dots, which suit applications in imaging and microscopy. We find that the TPEF rate is directly proportional to the measured7 degree of second-order coherence, as predicted by theory. Our results show that photon bunching in thermal light can be exploited in two-photon microscopy, with the photon statistic providing a new degree of freedom.

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Figure 1: Sketch of the experimental set-up.
Figure 2: Comparison of excitation with thermal and coherent light.


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The authors thank J. Kiethe for help with g(2) measurements and D. Puhlmann for helping with the preparation of the graphics for the manuscript. This work was funded by the German Federal Ministry for Education and Research (BMBF), Germany (grant no. 13N11131).

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M.S., A.H. and R.M. designed the experiment. H.K., A.J. and M.S. conducted the experiment, collected the data and analysed the data. The manuscript was prepared by A.J. with contributions from M.S., H.K., A.H. and R.M.

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Correspondence to Andreas Jechow.

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The authors declare no competing financial interests.

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Jechow, A., Seefeldt, M., Kurzke, H. et al. Enhanced two-photon excited fluorescence from imaging agents using true thermal light. Nature Photon 7, 973–976 (2013).

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