Due to their special beam profile, Bessel beams offer advantageous properties for micro-drilling and internal volume processing, especially for transparent materials. In addition, the laser power of industrial ultrashort pulsed lasers has increased significantly in recent years, offering the possibility of highly efficient processes using multispot profiles. We report on optical simulations and an experimental optical setup for generating multiBessel beams by combining a refractive axicon and a spatial light modulator. This setup offers a new possibility of multiBessel beam generation by functional division of the Bessel beam generation by the axicon and the possibility of separation flexible beam splitting by a spatial light modulator. The beam profiles generated with this setup are analyzed and compared in this study using optical simulations and experiments. In addition to the analysis of the Bessel beams in the machining plane, they are also analyzed in the propagation direction by means of intensity distributions measured by a camera in small-step z positions. Furthermore, the experimental applicability of the module-based beam shaping system is demonstrated by integrating into an existing laser system.
Optical elements are usually fabricated via conventional well-established processes - milling, grinding and polishing. However, these techniques cannot fully satisfy the growing demand for miniaturized optics with tailored properties. An alternative technology is a laser-based fabrication, including the ultrashort laser ablation and the subsequent CO2 laser polishing steps. Although this technique allows complex surface structuring, the fabricated optics require validation. In this contribution, we present the characterization of the laser-fabricated axicon from fused silica and comparison with the conventional element. We demonstrate that laser-fabricated axicon can generate the high-quality optical Bessel beam with a long non-diffractive length, which could be applied for 1 mm-thick glass intra-volume dicing. Furthermore, we demonstrate that the astigmatic aberrations, introduced via axicon tilt operation, allow generation of the asymmetrical intensity pattern, which could enhance the cleavability of modified glass sheets. The scribing process was optimized by the variation of processing parameters to minimize the force, required to separate modified glass sheets, using the fourpoint bending setup. Furthermore, the quality of the generated beam and volumetric scribing performance was compared to the conventional commercial oblate-tip axicon.
We report on a photonic process chain to manufacture optical elements by non-contact all laser based micro-processing. Firstly, pre-defined optics geometries are generated by high-precision 1030 nm femtosecond layer-by-layer ablation. In order to meet high surface quality requirements, inevitable stipulated for optical use, the surface of thus generated elements has to be smoothened by subsequent 10.6 μm CO2 laser polishing. To demonstrate this surface finishing process, a complex optic geometry i.e. an axicon array consisting of 37 individual axicons is fabricated within 23 minutes while the polishing shows a reduction of the surface roughness from 0.36 μm to 48 nm. The functionality of the fabricated optic is tested using the 1030 nm wavelength ultrashort pulsed laser. Several sub-Bessel beams exhibiting the typical zeroth-order Bessel beam intensity distribution are observed, in turn confirming the applied manufacturing process to be well applicable for the fabrication of complex optic geometries. Cross sections of the quasi-Bessel beam at the axicon in the middle of the array in both, x- and y-direction, show an almost identical intensity profile, indicating the high contour accuracy of the axicon. Detailed investigations of the axicon in the middle of the array show a tip rounding of 1.37 mm while the sub-beam behind this axicon is measured to have a diameter of 9.5 μm (FWHM) and a Bessel range in propagation direction of 8.0 mm (FWHM).
We report on an all-laser based fabrication process for optical elements made of glass. Two laser systems, namely a 1030 nm ultrashort pulsed and a CO2 laser are applied. Firstly, a femtosecond laser is used to precisely ablate the glass substrate layer-wise, forming the designed geometry. This ablation process is investigated in detail, focusing on the influence of the pulse distance as well as the laser fluence on the ablation depth, ablation efficiency and the surface roughness. It is found that the ablation depth decrease with increasing pulse distance while the ablation efficiency shows a maximum in the middle of the pulse distance regime for all investigated fluences. Contrary to these results, no significant influence on the surface roughness is observed. The well developed ultrashort pulsed laser ablation process is demonstrated for the fabrication of optical preforms such as cone-shaped (axicon), spherical and cylindrical lenses. In order to meet high surface quality requirements, inevitable stipulated for optical use, the surface roughness of the generated elements has to be reduced by CO2 laser polishing. To demonstrate the subsequent surface finishing process, a complex optic geometry i.e. an axicon array consisting of 37 individual axicons is fabricated within 23 minutes while the polishing shows a reduction of the surface roughness from 0.36 μm to 48 nm. For a detailed investigation of the fabricated optic, the axicon array is mounted into the ultrashort pulsed laser machine. Several sub-Bessel beams exhibiting the typical zeroth-order Bessel beam intensity distribution are observed, in turn confirming the applied manufacturing process to be well applicable for the fabrication of complex optic geometries. Cross-sections of the quasi-Bessel beam at the axicon in the middle of the array in both, x- and y-direction, show an almost identical intensity profile, indicating the high contour accuracy of the axicon. The diameter of the sub-beam is measured to be 9.5 μm (FWHM) and the Bessel range in propagation direction amounts to 8.0 mm (FWHM).
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