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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Denk, W., Strickler, J. & Webb, W. Two-photon laser scanning fluorescence microscopy. Science 248, 73–76 (1990).
Fei, H.-B., Jost, B. M., Popescu, S., Saleh, B. E. A. & Teich, M. C. Entanglement-induced two-photon transparency. Phys. Rev. Lett. 78, 1679–1682 (1997).
Jechow, A., Heuer, A. & Menzel, R. High brightness, tunable biphoton source at 976 nm for quantum spectroscopy. Opt. Express 16, 13439–13449 (2008).
Gatti, A., Brambilla, E., Bache, M. & Lugiato, L. A. Ghost imaging with thermal light: comparing entanglement and classical correlation. Phys. Rev. Lett. 93, 093602 (2004).
Cao, D.-Z., Ge, G.-J. & Wang, K. Two-photon subwavelength lithography with thermal light. Appl. Phys. Lett. 97, 051105 (2010).
Zhu, J., Chen, X., Huang, P. & Zeng, G. Thermal-light-based ranging using second-order coherence. Appl. Opt. 51, 4885–4890 (2012).
Boitier, F., Godard, A., Rosencher, E. & Fabre, C. Measuring photon bunching at ultrashort timescale by two-photon absorption in semiconductors. Nature Phys. 5, 267–270 (2009).
Hanbury Brown, R. & Twiss, R. Q. Correlation between photons in two coherent beams of light. Nature 177, 27–29 (1956).
Glauber, R. J. The quantum theory of optical coherence. Phys. Rev. 130, 2529–2539 (1963).
Göppert-Mayer, M. Über Elementarakte mit zwei Quantensprüngen. Ann. Phys. (Berlin) 401, 273–294 (1931).
Kaiser, W. & Garrett, C. G. B. Two-photon excitation in CaF2: Eu2+. Phys. Rev. Lett. 7, 229–231 (1961).
Teich, M. C. & Wolga, G. J. Multiple-photon processes and higher order correlation functions. Phys. Rev. Lett. 16, 625–628 (1966).
Lambropoulos, P., Kikuchi, C. & Osborn, R. K. Coherence and two-photon absorption. Phys. Rev. 144, 1081–1086 (1966).
Mollow, B. R. Two-photon absorption and field correlation functions. Phys. Rev. 175, 1555–1563 (1968).
Shiga, F. & Imamura, S. Experiment on relation between two-photon absorption and coherence of light. Phys. Lett. A 25, 706–707 (1967).
Pittman, T. B., Shih, Y. H., Strekalov, D. V. & Sergienko, A. V. Optical imaging by means of two-photon quantum entanglement. Phys. Rev. A 52, R3429–R3432 (1995).
Saleh, B. E. A., Abouraddy, A. F., Sergienko, A. V. & Teich, M. C. Duality between partial coherence and partial entanglement. Phys. Rev. A 62, 043816 (2000).
Ragy, S. & Adesso, G. Nature of light correlations in ghost imaging. Sci. Rep. 2, 651 (2012).
Karmakar, S., Meyers, R. & Shih, Y. H. Ghost imaging experiment with sunlight compared to laboratory experiment with thermal light. Proc. SPIE 8518, 851805 (2012).
Lee, T.-P., Burrus, C. A. & Miller, B. I. A stripe-geometry double-heterostructure amplified-spontaneous-emission (superluminescent) diode. IEEE J. Quant. Electron. 9, 820–828 (1973).
Blazek, M. & Elsäßer, W. Coherent and thermal light: tunable hybrid states with second-order coherence without first-order coherence. Phys. Rev. A 84, 063840 (2011).
Xu, C. & Webb, W. W. Measurement of two-photon excitation cross sections of molecular fluorophores with data from 690 to 1050 nm. J. Opt. Soc. Am. B 13, 481–491 (1996).
Taylor, M. A. et al. Biological measurement beyond the quantum limit. Nature Photon. 7, 229–233 (2013).
Boitier, F. et al. Photon extrabunching in ultrabright twin beams measured by two-photon counting in a semiconductor. Nature Commun. 2, 425 (2011).
Aßmann, M., Veit, F., Bayer, M., van der Poel, M. & Hvam, J. M. Higher-order photon bunching in a semiconductor microcavity. Science 325, 297–300 (2009).
Stevens, M. J. et al. High-order temporal coherences of chaotic and laser light. Opt. Express 18, 1430–1437 (2010).
Jechow, A. et al. Stripe-array diode-laser in an off-axis external cavity: theory and experiment. Opt. Express 17, 19599–19604 (2009).
Jechow, A., Schedel, M., Stry, S., Sacher, J. & Menzel, R. Highly efficient single-pass frequency doubling of a continuous-wave distributed feedback laser diode using a PPLN waveguide crystal at 488 nm. Opt. Lett. 32, 3035–3037 (2007).
Ryan, R. E., Westling, L. A., Blümel, R. & Metcalf, H. J. Two-photon spectroscopy: a technique for characterizing diode-laser noise. Phys. Rev. A 52, 3157–3169 (1995).
Agarwal, G. S. Field-correlation effects in multiphoton absorption processes. Phys. Rev. A 1, 1445–1459 (1970).
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).
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). https://doi.org/10.1038/nphoton.2013.271
Communications Physics (2018)