A well-known and already having many material processing applications zero-order Bessel beam makes a great base for improvements to have even broader applicability. In our work, we analyze vector Bessel beams (VBB), which can be generated with high efficiency and quality via the use of Geometric Phase Optical Elements. The beam transverse polarization distribution enables to change intensity distribution easily, i.e. a polarizer in front of the beam will generate invariant over the propagation multi-peak ring- the shaped structure which could be very beneficial to modify material at multiple sights with a single laser shot. We analyze higher-order VBB generated modifications in thin glass and analyze the applicability for etching of large diameter holes.
Long focal lines with transverse spot sizes as small as a few wavelengths are called optical needles. A zeroth order Bessel beam being a good example is widely used in such applications as laser micromachining. In practice Bessel beam generated with an axicon has a peak in axial intensity distribution and is not only due to aberrations caused by planar dielectric material interface. Here, we investigate optical needles with controlled axial intensity distribution via intensity modulation of the incoming beam. We have chosen to generate constant axial intensity Bessel beam and propose spatial transmission mask to do so. Experimental verification is presented using diffractive optics elements based on Pancharatnam-Berry phase. We demonstrate a flattening of the axial intensity profile of the Bessel beam without the alteration to the optical needle diameter.
Non-diffracting Bessel beams and its modified versions are widely used in industry for transparent material micro processing purposes - cutting, drilling etc., due to generation of high aspect ratio micro voids. More and more applications of such beams involve manipulation of their transverse intensity profile to create unique tools for novel micro processing applications, for example, asymmetric and multi-peak transverse profiles create directional strain and crack in modified area for glass cutting, while other intensity patters may be used to create complex structures in multiphoton polymerization applications. In this work we demonstrate experimental generation of higher order vector Bessel beams which are notable for their ring-shaped transverse intensity profile together with multi-peak transverse polarization components, where ring diameter and number of peaks in separate polarization components depends on beams order. These unique beams were realized using axicon together with higher order s-plates - spatially variant waveplates based on femtosecond laser written nano gratings in fused silica glass substrates. Induced nanogratings withstands high intensity laser radiation without changing its spatial structure which allows us to use nanograting based elements for ultra-short high-power pulsed laser beam shaping. Generated higher order vector Bessel beams and their separate polarization components were used to inscribe modifications in transparent materials and to investigate beam`s applicability for ultra-fast laser micro processing purposes.
Beam profile engineering, where a desired optical intensity distribution is generated by phase shifting and/or amplitude changing elements, is a promising approach in various laser-related applications. For example, vector geometrical phase elements enable various flat special optical elements such as top-hat converters. We present a study on engineering efficient top-hat converters inscribed in the glass by femtosecond laser pulses. We start with an amplitude encoded top hat converter and demonstrate how its efficiency can be further increased by introduction of phase masks and by the polarization of the incident beam. Experimental verification of the concept is also presented.
Nondiffracting beams are known for their long line of focus, which has various applications in laser materials processing. Zeroth order Bessel beam is usually generated with an axicon and has a distinct circular spatial spectra. The nature of higher order Bessel beams, elliptical and parabolic nondiffracting beams is also conical and their spatial spectra have their own azimuthal modulation. We study numerically and verify experimentally generation of vortical Bessel beams, their superpositions along with elliptical and parabolical beams using an axicon. Laser induced modifications in glasses for various durations and beam powers using generated pulsed beams are analyzed.
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