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Observation of stimulated emission by direct three-photon excitation


Multiphoton processes, predicted1 theoretically in 1931, were for a long time considered to be mainly of academic interest. This view changed when it was shown2,3 that a two-photon absorption process could, because of a quadratic dependence of excitation on intensity, produce a spatially confined excitation useful for three-dimensional data storage and imaging. Two-photon absorption has received considerable attention recently because of the development of highly efficient two-photon-sensitive materials, leading to numerous technological applications4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28. These successes have created interest in exploring applications based on three-photon excitations29. For a three-photon process, a longer excitation wavelength such as those common in optical communications can be used. Also, the cubic dependence of the three-photon process on the input light intensity provides a stronger spatial confinement, so that a higher contrast in imaging can be obtained. Here we report the observation of a highly directional and up-converted stimulated emission as an amplified spontaneous emission, produced in an organic chromophore solution by a strong simultaneous three-photon absorption at 1.3 µm. This achievement suggests opportunities for a three-photon process in frequency-upconversion lasing, short-pulse optical communications, and the emerging field of biophotonics.

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Figure 1: Photographs showing highly directional, frequency-upconverted stimulated emission, pumped by three-photon absorption.
Figure 2: Spectra of the stimulated emission and induced fluorescence, pumped by three-photon absorption.
Figure 3: Streak-camera measurements.
Figure 4: Diagram showing the proposed mechanism for three-photon excitation and stimulated emission.
Figure 5: Output/input characteristics of three-photon-pumped stimulated emission.


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This work was supported by the US Air Force Office of Scientific Research, Washington DC, and the Polymer Branch of the US Air Force Research Laboratory at Dayton.

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Correspondence to Paras N. Prasad.

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The authors declare no competing financial interests.

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He, G., Markowicz, P., Lin, TC. et al. Observation of stimulated emission by direct three-photon excitation. Nature 415, 767–770 (2002).

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