title: Observation of stimulated emission by direct three-photon excitation.
abstract: Multiphoton processes, predicted theoretically in 1931, were for a long time considered to be mainly of academic interest. This view changed when it was shown 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 applications. These successes have created interest in exploring applications based on three-photon excitations. 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 microm. This achievement suggests opportunities for a three-photon process in frequency-upconversion lasing, short-pulse optical communications, and the emerging field of biophotonics.
authors.affiliation: Institute for Lasers, Photonics and Biophotonics, University at Buffalo, The State University at Buffalo, New York 14260-3000, USA.
authors.forename: Guang S
authors.initials: GS
authors.lastname: He
authors.forename: Przemyslaw P
authors.initials: PP
authors.lastname: Markowicz
authors.forename: Tzu-Chau
authors.initials: TC
authors.lastname: Lin
authors.forename: Paras N
authors.initials: PN
authors.lastname: Prasad
mesh_terms: D004396:Coloring Agents / Q000737:chemistry / Q000378:metabolism; D007834:Lasers; D008027:Light; D055095:Optics and Photonics / Q000295:instrumentation; D017785:Photons; D010789:Phototherapy
chemical_list: D004396:Coloring Agents