Martynas Beresna

Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass

We demonstrate the generation of optical vortices with radial or azimuthal polarization using a space variant polarization converter, fabricated by femtosecond laser writing of self-assembled nanostructures in silica glass. Manipulation of the induced form birefringence is achieved by controlling writing parameters, in particular, the polarization azimuth of the writing beam. The fabricated converter allows switching from radial to azimuthal polarization by controlling the handedness of incident circular polarization.

Polarization sensitive elements fabricated by femtosecond laser nanostructuring of glass [Invited]

We review recent progress in application of femtosecond laser nanostructuring of fused silica. The tight control of nanostructures’ properties through writing parameters is demonstrated implementing elements with unique optical properties, which can be widely used in material processing, microscopy, optical trapping and manipulation.

Ultrafast Manipulation of Self-Assembled Form Birefringence in Glass

Ultrashort pulse lasers have allowed probing of molecular dynamics in real time on the femtosecond time scale, with exotic behavior ranging from alignment of molecules and clusters, structural deformation, phase transitions on solid, and electron localization in magnetic materials. A recent progress in high power ultrashort pulse lasers has opened new frontiers in physics and technology of light-matter interactions from X-ray generation, nuclear fusion, laser surgery, integrated and fiber optics, optical data storage, to 3D micro- and nano-structuring. An intriguing phenomenon that currently attracts a lot of interest is the self-assembly of periodic nanostructures in the direction perpendicular to the light polarization. Uniaxial birefringence observed after femtosecond laser irradiation of silica glass has been explained by induced nanogratings and referred as self-assembled form birefringence. Self organization process has been interpreted in terms of the interference of electron plasma waves resulting in electron concentration modulation, followed by freezing of the interference pattern by structural change in glass. However, the mechanism including dynamics of self-organized nanostructures formation is still not fully understood. Recently, a double-pulse pump-probe configuration was used to enhance ablation in fused silica and silicon. In similar experiments molecular ensembles with an oriented angular momentum were produced. Here, we describe the ultrafast writing dynamics of form birefringence produced by self-organized nanogratings in double pulse experiments. Rewritable five-dimensional (5D) optical data storage using self-assembled form birefringence was demonstrated.

Polarization diffraction grating produced by femtosecond laser nanostructuring in glass

We demonstrate polarization sensitive diffractive optical element fabrication by femtosecond direct writing in the bulk of silica glass. Modulation of the anisotropic properties is produced by controlling light-induced self-assembled nano-gratings.

Ultrafast laser direct writing and nanostructuring in transparent materials

An overview of recent achievements in the field of femtosecond laser writing in transparent materials is presented. Thanks to the unique properties of light–matter interaction on the ultrashort time scale, this direct writing technique has led to observation of unique phenomena, including nonreciprocal writing and anisotropic photosensitivity, in transparent materials and allowed engineering of novel photonic devices.

Dependence of the femtosecond laser refractive index change thresholds on the chemical composition of doped-silica glasses

The refractive index changes in doped silica are investigated. We observed that the permanent isotropic index change threshold (T1) is not significantly dependent on the doping. We show that strong birefringence (permanent linear birefringence) exists in doped silica but its threshold (T2) exhibits significant dependence on the used dopants. In our conditions, comparing with silica (0.31 μJ/pulse here), for 1.5 at% Ge-doped silica the T2 threshold is smaller (0.14 ± 0.05 μJ/pulse). For a silica doped with 0.3 at% of fluorine, T2 is close to 1.20 ± 0.05 μJ/pulse. An interpretation is given not only about threshold variation but also about RIC for energies beyond. It is based on the overcoming of relaxation time in the volume interaction.

Photosensitivity control of an isotropic medium through polarization of light pulses with tilted intensity front

We present the first experimental evidence of anisotropic photosensitivity of an isotropic homogeneous medium under uniform illumination. Our experiments reveal fundamentally new type of light induced anisotropy originated from the hidden asymmetry of pulsed light beam with a finite tilt of intensity front. We anticipate that the observed phenomenon, which enables employing mutual orientation of a light polarization plane and pulse front tilt to control interaction of matter with ultrashort light pulses, will open new opportunities in material processing.

Exciton mediated self-organization in glass driven by ultrashort light pulses

We propose an exciton-polariton-mediated self-organization effect in transparent SiO2 glass under intense femtosecond light irradiation. Interference and dipole-dipole interaction of polaritons causes formation of gratings of dielectric polarization. Due to an ultrafast exciton self-localization into a quasicrystal structure, the polariton gratings remain frozen in glass and a permanent three-dimensional image of exciton-polariton gas is created. We show that coherent effects in propagation of exciton-polaritons can serve as a tool for nanostructuring and fabrication of 5-dimensional optical memories in glass, opening new horizons for polaritronics.

Extraordinary anisotropy of ultrafast laser writing in glass

The unusual dependence of femtosecond laser writing on the light polarization and direction of raster scanning is demonstrated in silica and chalcogenide glasses. Two different mechanisms contributing to the observed anisotropy are identified: the chevron-shaped stress induced by the sample movement and the pulse front tilt of ultrashort light pulse. Control of anisotropies associated with the spatio-temporal asymmetry of an ultrashort pulse beam and scanning geometry is crucial in the ultrafast laser machining of transparent materials.

Stress distribution around femtosecond laser affected zones: effect of nanogratings orientation

Under certain exposure conditions, femtosecond lasers create nanogratings in the bulk of fused silica for which the orientation is governed by the laser polarization. Such nanostructure induces stress that affects optical and chemical properties of the material. Here, we present a method based on optical retardance measurement to quantify the stress around laser affected zones. Further, we demonstrate stress dependence on the nanogratings orientation and we show that the stress within single nanogratings lamellae can locally be as high as several gigapascals.