Characterization, comparison, and choice of a commercial double-clad fiber for nonlinear endomicroscopy

Abstract. Several endomicroscope prototypes for nonlinear optical imaging were developed in the last decadefor in situ analysis of tissue with cellular resolution by using short infrared light pulses. Fourier-transform-limitedpulses at the tissue site are necessary for optimal excitation of faint endogenous signals. However, obtainingthese transform-limited short pulses remains a challenge, and previously proposed devices did not achieve anoptimalpulse delivery.Wepresent astudy offibered endomicroscopearchitecturewithan efficientfemtosecondpulse delivery and a high excitation level at the output of commercially available double-clad fibers (DCFs). Theendomicroscope incorporates a module based on a grism line to compensate for linear and nonlinear effectsinside the system. Simulations and experimental results are presented and compared to the literature.Experimentally, we obtained short pulses down to 24 fs at the fiber output, what represents to the best ofour knowledge the shortest pulse duration ever obtained at the output of a nonlinear endoscopic system withoutpostcompression.ThechoiceoftheoptimalDCFamongfourpossiblecommercialcomponentsisdiscussedandevaluated in regard to multiphoton excitation and fluorescence emission.