Freie Universität Berlin, Germany
Title: Shaped laser pulses after optical fibers for selective multiphoton excitation of biomolecules
Biography: Albrecht Lindinger
Recently, ultrashort laser pulses were increasingly used for multiphoton excited imaging in biological samples. Fluorescent molecules were employed to distinguish between tissue structures, and a high contrast is favourable for microscopic imaging. Thereto, laser pulse shaping provides a powerful tool by tailoring the pulses such that two species may selectively be excited. In particular, tailoring of laser pulses is applied to exploit intrapulse interference effects in multiphoton excited fluorescence. Furthermore, pulse shaping is successfully used to control photo-induced processes. Novel pulse shaping schemes for simultaneous phase, amplitude, and polarization control were designed in recent years, and a parametric subpulse encoding was developed. Thereby, physically intuitive parameters like chirps and polarization states can be controlled. This yields new perspectives of utilizing all properties of the light field in the pulse modulation. This contribution describes pulse shaping methods for improved multiphoton excited fluorescence contrast after transmitting a nanostructured kagome fiber. The distortions due to the optical fiber properties are precompensated to receive predefined shaped pulses at the distal end of the fiber. Special antisymmetric phase functions are employed for scans of the multiphoton excitation fluorescence. Application of phase-shaped pulses for imaging contrast enhancement is demonstrated for the autofluorescing vitamins A and B2. Moreover, particularly phase and polarization tailored pulses are employed to optimally excite one dye in one polarization direction and simultaneously the other dye in the other polarization direction. The presented method has a high potential for endoscopic applications due to the unique kagome fiber properties for imaging of endogenous fluorophores.