Spectro-temporal dispersion management of femtosecond pulses for fiber-optic two-photon endomicroscopy

Abstract

The emerging fiber-optic two-photon endomicroscopy technology holds a strong promise for enabling translational applications of nonlinear optical imaging. Effective femtosecond pulse dispersion management is critical for achieving high-quality imaging. Here we report systematic analyses and performance characterization of a dual-fiber spectro-temporal dispersion management scheme involving a grating pair as the pulse stretcher. Compared with conventional linear-only compensation, the grating-based spectro-temporal compensation also takes into account nonlinear effects and enhances the two-photon signal by ~3-fold as experimentally demonstrated. Numerical simulations were carried out to systematically investigate the influence of several key design parameters on the overall compensation efficacy. Furthermore, comprehensive performance comparison with an ideal grism-pair counterpart reveals that a grating-pair stretcher affords much higher power throughput and thus is preferable for portable endomicroscopy systems with limited laser source power.

Label-free imaging of human brain tissue at subcellular resolution for potential rapid intra-operative assessment of glioma surgery

“…The excitation laser from a tunable Ti:sapphire laser (<150 fs, Chameleon Ultra II, Coherent, Inc., CA, USA) was delivered to the sample through the core of the DCF in the endomicroscope. A grating pair and a dual-fiber scheme were used to manage the temporal pulse properties 24 . Fluorescence signals were epi-collected through an achromatic miniature objective into the inner clad of the DCF, and then guided back to the proximal end of the endomicroscope, where they were first separated from the excitation light by a dichroic mirror, and then further filtered for each of the two channels with a 496 nm long-pass optical filter for the FAD and a 447/60 nm band-pass optical filter for the NADH signals before finally being collected by a PMT.…”

Label-Free Metabolic Imaging In Vivo by Two-Photon Fluorescence Lifetime Endomicroscopy

“…Detailed descriptions about these measures and the resultant SNR enhancement have been reported elsewhere. 44,47 Time-Resolved Data Acquisition. For each fluorescence photon detected, the photomultiplier tube (PMT; H7422P-40, Hamamatsu Photonics) generates a photocurrent pulse, which is converted using a high-speed transimpedance preamplifier (HFAC-26 dB, Becker & Hickl GmbH) to a voltage pulse and finally registered as an emission event using a commercial TCSPC module (SPC 150, Becker & Hickl GmbH) that is synchronized with the periodic excitation pulse train.…”

“…Major SNR-enhancing measures developed for our 2p-FLeM system include (1) achromatizing the miniature objectives with remarkably reduced back focal shift (i.e., the DCF-facing side) to facilitate epifluorescence collection, (2) customizing the DCF with a pure-silica single-mode core to suppress the in-fiber nonlinear background luminescence and an enlarged (∼185 μm in diameter), high-acceptance NA (∼0.3) inner clad to increase the system collection etendue, and (3) adopting a dual-fiber setup that handles both linear and nonlinear dispersions experienced by femtosecond laser pulses propagating in a single-mode core, minimizes the pulse-width broadening at the distal end, and significantly promotes the excitation efficiency. Detailed descriptions about these measures and the resultant SNR enhancement have been reported elsewhere. , …”

Two-Photon Endoscopy: State of the Art and Perspectives

“…With such wide bandwidth, the dispersion of the media becomes much more complex, and SOD compensation is not enough. While stretcher consisting of diffraction gratings was shown to be applicable in the systems where endoscope fiber is relatively short [ 30 ], it is shown that conventional grating-pair compressor cannot be designed with zero TOD [ 31 ]. For this reason, a more sophisticated stretcher was introduced, combined with diffraction gratings and prisms used in a very close assembly, creating grism elements [ 32 , 33 ] (Fig.…”