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Polarization plays a crucial role in light–matter interactions; hence its overall manipulation is an essential key to unlock the versatility of light manufacturing, especially in femtosecond laser direct writing. Existing polarization-shaping techniques, however, only focus on their manipulation in the transverse plane of light beams, i.e., two-dimensional control. In this paper, we propose a novel passive strategy that exploits a class of femtosecond laser written space varying birefringent elements to shape the polarization state along the optical path. As a demonstration, we generate a three-dimensional structured Bessel beam whose linear polarization state slowly evolves along the focus (typ. 90° within 60λ). Such a "helically polarized" Bessel beam allows imprinting "twisted nanogratings" in SiO2 glass which result in an extrinsic optical chirality at a micrometric scale and own a high optical rotation. Our work provides new perspectives for three-dimensional polarization manipulation and insights into applications in structured light, light–matter interaction, and chiral device fabrication. [ABSTRACT FROM AUTHOR]

The fluorescence from living bacteria (Bacillus subtilis, Enteroccocus and Escherichia coli), induced by a ultrashort 270 nm pump pulse is depleted up to 50% by an optically delayed ultrafast 810 nm probe pulse in a pump-probe arrangement. The fast (subpicosecond) fluorescence decrease occurs for a pump-probe delay of Δt>2 ps. Depletion is also observed for tryptophan in water in contrast with organic cyclic molecules such as naphtalene or diesel fuel, despite similar absorption and fluorescence spectra. This remarkable difference allows us to propose a new remote sensing method able to efficiently discriminate organic from biological aerosols in highly populated urban areas. [ABSTRACT FROM AUTHOR]

We demonstrate that ultrashort and ultraintense light filaments survive their interaction with water droplets as large as 95 mm and that they are transmitted through water clouds having an optical thickness as high as 3.2 (transmission 5%). In contrast with linear optics, this remarkable transmission through optically dense media results from a dynamic energy balance between the quasisolitonic structure and the surrounding laser photon bath, which acts as an energy reservoir. Implications for free-space laser communications, remote sensing, and telemetry are discussed. [ABSTRACT FROM AUTHOR]