Light Source Optimization and Characterization for Multimodal Nonlinear Optical Microscopy

Abstract

The Ti:sapphire laser is a very useful laser which provides advantages such tunability and ultrashort pulses <10 fs. The low noise, good mechanical and thermal properties provide coherent pulses very convenient for nonlinear process. This laser has seen increasing interest in various fields from physics to biological sciences and must be optimized for practical performances.

This thesis presents methods for Ti:sapphire characterization and optimization based on the spatial shape of the beam involving the divergence and the beam quality factor. The temporal shape of the pulse defined by the pulse duration and the temporal shape of the pulse. This characterization will be done optimized for multi-photon microscopy and the optimum parameters for practical performances will be defined.

The Ti:sapphire laser divergence is first experimentally defined as a collimated beam with a beam quality factor ≤ 1.15. The pulse shape is determined with an interferometric autocorrelation as hyperbolic secant squared shape which achieved 44 fs pulse duration for 760 nm, 45 fs for 800 nm and 70 fs for 870 nm. The Ti:sapphire laser is then demonstrated in a multi-photon microscopy setup where the dispersion from the microscope has to be compensated by a chirped mirror pair. An application for a future stimulated Raman spectroscopy setup involving supercontinuum generation with photonic crystal fibers in combination with the tunable femtosecond Ti:sapphire laser is described. In total, 6 different fibers are tested and the supercontinuum characterized.