Characterization of optical polarization converters made by femtosecond laser writing

Recently, new types of silica polarization converters fabricated by femtosecond lasers have been introduced. These devices use spatially arranged nanogratings found under certain femtosecond laser exposure conditions in fused silica to create arbitrary polarization states by shaping spatially and locally the retardance of an incoming beam. Using this principle, radial and azimuthal polarization converters were demonstrated. These devices make use of a large density of femtosecond laser spots, introducing localized defects, affecting the performance of the converter. To optimize the writing and the post-processing annealing step of these kind of devices, here we introduce a novel fluorescence lifetime imaging microscope (FLIM) working with deep UV (240-280 nm) wavelength excitations. Specifically, we demonstrate the potential of this technique and more generally, how it can be used for characterizing a variety of femtosecond laser induced modifications in fused silica. This UV-FLIM can be used with micro-fluidic and bio-samples to characterize temporal characteristics of fluorescence.