Ultrafast laser nanostructuring for photonics and information technology

The field of ultrafast laser nanostructuring is growing rapidly with the need to search for more advanced fabrication solutions, medium possessing the advantages of both flexibility and tunable optical properties which can be effectively exploited for the integration of polarization sensitive modifications into optical elements and multidimensional optical data storage.Any material that support nanogratings are of interest for being explored for multidimensional data storage. Therefore, the self-assembled nanostructures by femtosecond laser irradiation are explored in several different materials, such as alkali-free alumina-borosilicate glass, GeO2 glass, and indium-tin-oxide (ITO) thin film. The growth of the induced retardance associated with the nanograting formation in alumina-borosilicate glass is three orders of magnitude slower than in silica glass. The pulse energy for maximum retardance in GeO2 glass is ~65% lower than in fused silica. Direct-write femtosecond laser nanostructuring of ITO thin film is also demonstrated where the deep-subwavelength ripples with periodicity of down to 120 nm are realized originating the form birefringence (|Δn| ≈ 0.2), which is 2 orders of magnitude higher than the commonly observed in uniaxial crystals or femtosecond laser nanostructured fused quartz.The comparison of a femtosecond laser induced modification in silica matrices with three different degrees of porosity is given. The maximum retardance value achieved in porous glass is twofold higher than in fused silica, and tenfold greater than in aerogel. The polarization sensitive structuring in porous glass by two pulses of ultrafast laser irradiation is demonstrated, as well as no observable stress is generated at any conditions.Applying the acquired knowledge along with full control of laser system, the polarization sensitive elements are combined into multidimensional data storage providing the main processing conditions required for sufficient practical implementation of the technique. Finally, the proposed improvements in terms of high capacity and high density elevate the technology and potentially push the currently known boundaries to the higher level

Generation of extreme ultraviolet vector beams from infrared laser pulses

Vector beams are light beams with spatially variant polarization. During the last decade vector beams have become an indispensable tool in many areas of science and technology such as optical trapping, quantum memories, and quantum optics. In particular, radially and azimuthally polarized light beams are the paradigm of vector beams. Radial vector beams are especially interesting due to the non-vanishing longitudinal electric field component present in tightly focusing systems, which allows to sharply focus light below the diffraction limit. On the other hand, azimuthal vector beams can induce longitudinal magnetic fields with potential applications in spectroscopy and microscopy. However, the spectral limitations of the generation techniques of vector beams based on linear optics prevent their efficient generation in the extreme-ultraviolet (EUV) and x-ray regimes, which would further extend their applications down to the nanometric scale. High-order harmonic generation (HHG) is known as a unique non-perturbative frequency up-conversion process for the generation of coherent EUV and soft x-ray radiation. A remarkable aspect of HHG is its fully coherent nature, mapping the characteristics of the driving field to the high frequency spectral region and thus allowing to harness the angular momentum properties of the harmonic radiation through modifications of the driving field.In this work EUV vector beams are generated for the first time using HHG. To do so, an infrared fs radially polarized vector beam –generated with a s-waveplate – is focused into an argon gas target, whose atoms emit coherent EUV radiation through HHG. Our experimental and theoretical results demonstrate that HHG imprints the polarization state of the infrared beam, ranging from radial to azimuthal, into the higher frequency radiation. Our numerical simulations also demonstrate that the generated high-order harmonic beams can be synthesized into attosecond vector beams in the EUV/soft x-ray regime. Our proposal overcomes the state of the art limitations for the generation of vector beams far from the visible domain and could be applied in fields such as diffractive imaging, EUV lithography, or ultrafast control of magnetic properties

Towards the generation of broadband optical vortices: extending the spectral range of a q-plate by polarization-selective filtering

Optical vortex beams in the visible and near-infrared spectrum over a wide spectral region are generated by a single S-waveplate polarization converter using polarization-selective filtering. A spectral coverage of 600 nm is demonstrated, with maximum efficiency at a wavelength of 530 nm. The broadband coverage is obtained using polarization filtering, which is applicable for any component based on geometric phase retardation. The efficiency of the filtering varies from 50% to 95% depending on the wavelength. This technique has potential application in stimulated emission microscopy and lithography