From Event: SPIE Optical Engineering + Applications, 2016
Non-degenerate 2-photon excitation of a fluorophore with two laser beams of different photon energies may offer independent degree of freedom in tuning of the photon flux (i.e., the power) for each beam. Wereport a practical demonstration that the emission intensity of a fluorophore excited in the non-degenerate regime in scattering medium is more efficient than the commonly used degenerate 2-photon excitation. In our experiments we use spatially and temporally aligned Ti:Sapphiremode-locked laser and optical parametric oscillator beams operating at near infrared (NIR) and short-wavelength infrared (SWIR) optical frequencies, respectively. The non-degenerate 2-photon excitation mechanism takes advantage of the infrared wavelengths used in 3-photon microscopy to achieve increased penetration depth, while preserving relatively high 2-photon excitation cross section, exceeding that achievable with the 3-photon excitation. Importantly, independent control of power for each beam implies that the flux requirement for the higher photon energy NIR beam, which experiences higher scattering in biological tissue, can be relaxed at the expense of increasing the flux of the lower photon energy SWIR beam which experiences lower scattering, thus promising deeper penetration with higher efficiency of excitation.Applications for in vivo brain imaging will be also discussed.
Yeshaiahu Fainman, Mu-Han Yang, Maxim Abashin, Payam Saisan, Peifang Tian, Christopher Ferri, and Anna Devor, "Non-degenerate 2-photon excitation for fluorescence microscopy in scattering medium
(Conference Presentation)," Proc. SPIE 9956, Ultrafast Nonlinear Imaging and Spectroscopy IV, 995615 (Presented at SPIE Optical Engineering + Applications: August 30, 2016; Published: 2 November 2016); https://doi.org/10.1117/12.2238599.5170791524001.
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