TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Current results on laser-based production of complex optics in glass T2 - 10. Wetzlarer Herbsttagung "Moderne Optikfertigung", 29. - 30. September 2020, Wetzlar KW - Laserbearbeitung KW - Fertigungstechnik Y1 - 2020 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UKP-Prozess mit anschließendem CO2-Laserpolieren zur Fertigung komplexer Optiken T2 - 10. Workshop Laserbearbeitung von Glaswerkstoffen KW - Linse KW - Array KW - Laserbearbeitung KW - Ultrakurzzeitlaser KW - Kohlendioxidlaser Y1 - 2020 ER - TY - JOUR A1 - Götzendorfer, Babette A1 - Mohr, Thomas A1 - Hellmann, Ralf T1 - Hybrid Approaches for Selective Laser Sintering by Building on Dissimilar Materials JF - Materials KW - Laserstrahlsintern Y1 - 2020 U6 - https://doi.org/doi.org/10.3390/ma13225285 VL - 2020 IS - 13 (22) SP - 5285 EP - 5296 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Rapid fabrication of precise glass axicon arrays by an all laser-based manufacturing technology JF - Journal of Laser Applications KW - Femtosekundenlaser Y1 - 2020 VL - 32 IS - 1 SP - 012001 EP - 012001 ER - TY - CHAP A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Internal micro structuring of transparent optical polymers by fs laser T2 - Laser-based Micro-and Nanoprocessing XIV 2020 N2 - Lab-on-chip systems are based on components to transport, mix, separate and analyse small volumes of different fluids. The consecutive integration of more complex functions into a single and compact chip demands on multilayer systems. As the classical production using a stacking and joining of single processed layers is elaborate and limited in terms of multilayer structures, an uprising trend to fabricate those devices is the internal, three dimensional processing of transparent substrates by using ultrashort laser pulses. In this study, we report on the generation of internal hollow architectures created by focused 514nm femtosecond laser pulses inside optical polymer bulk materials of different polymers. The three-dimensional channel layout is implemented by moving the sample using three-dimensional motorized stages, allowing arbitrary complex shaped internal channel architectures. Size and cross sectional shape of a single internal generated microchannel are determined by the intensity distribution of the focal voxel. In particular, we show a comprehensive parameter study to improve this laser process with respect to a higher processing speed and stability. KW - Femtosekundenlaser Y1 - 2020 U6 - https://doi.org/10.1117/12.2543487 VL - 11268 SP - 112681L PB - International Society for Optics and Photonics ER - TY - JOUR A1 - Roth, Gian-Luca A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Microchannels inside bulk PMMA generated by femtosecond laser using adaptive beam shaping JF - Optics Express N2 - In this contribution, we report on the generation of internal microchannels with basically unlimited channel length inside of PMMA bulk material by femtosecond laser. A precisely controllable and stable circular channel cross section is obtained by using a spatial light modulator to compensate the writing depth depending spherical aberration. Furthermore, the generation of a rotatable elliptical input beam by adaptive optics ensures a fitting of the beam shaping to the writing direction. In this study, we report on both, the effect of the ellipticity of the input beam and the effect of a correction of the spherical aberration on the circularity of the resulting internal microchannels. Moreover, we demonstrate the application of this writing technique by creating microfluidic testing structures inside of a transparent standard polymer. KW - Femtosekundenlaser KW - Polymethylmethacrylate Y1 - 2020 VL - 28 IS - 4 SP - 5801 EP - 5811 ER - TY - JOUR A1 - Rung, Stefan A1 - Bokan, Kevin A1 - Schwarz, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Influence of laser wavelength on the modification of friction between 100Cr6 steel and polytetrafluoroethylene by femtosecond laser-induced periodic surface structures JF - Journal of Laser Applications KW - Femtosekundenlaser Y1 - 2020 U6 - https://doi.org/10.2351/7.0000036 VL - 32 IS - 3 SP - 032017-1 EP - 032017-6 ER - TY - JOUR A1 - Roth, Gian-Luca A1 - Hessler, Steffen A1 - Kefer, Stefan A1 - Girschikofsky, Maiko A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers JF - Optics Express N2 - We report on a femtosecond laser based fabrication technique that enables simultaneous single-step generation of optical waveguides and Bragg gratings inside bulk cyclic olefin copolymers. Due to the nonlinear absorption of focused and spatially modulated laser radiation with a wavelength of 514 nm and a pulse duration of 450 fs, a modification concluding a refractive index shift increase inside the substrate can be achieved. A sophisticated characterization of the generated waveguides by means of an elaborate cut-back method reveals a maximum attenuation of 3.2 dB/cm. Additionally, a Mach-Zehnder interferometer is used to examine the waveguide’s refractive index profile. The integrated Bragg grating structures exhibit reflectivities up to 95 % and a spectral full width at half maximum of 288 pm, at a Bragg wavelength of 1582 nm, whereas the grating period can be deliberately chosen by adapting the fabrication parameters. Thus, due to its increased flexibility and the resulting dispensability of cost-intensive phase masks, this method constitutes an especially promising fabrication process for polymer Bragg gratings inside of bulk materials. KW - Femtosekundenlaser KW - Wellenleiter KW - Bragg-Reflektor Y1 - 2020 U6 - https://doi.org/10.1364/OE.388364 VL - 28 IS - 12 SP - 18077 EP - 18084 ER - TY - JOUR A1 - Roth, Gian-Luca A1 - Haubner, Julian A1 - Kefer, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Fs-laser based hybrid micromachining for polymer micro-opto electrical systems JF - Optics and Lasers in Engineering N2 - We report on femtosecond laser direct writing of electrically conductive copper structures on transparent cyclic olefin copolymer based planar optical chips. The process is based on a laser-induced reduction of CuO nanoparticles dissolved in a water-soluble resin. Thus generated conductive copper structures are characterized with respect to their chemical composition and electrical resistivity. In addition, the application of ultrashort laser pulses enables a hybrid micromachining approach comprising ablation of polymer substrates and the fabrication of copper patterns in a single laser processing setup. A possible electro-optical application of this approach is demonstrated by employing the copper structures as an electro-thermal microheater in combination with a polymer planar optical Bragg grating sensor. This, in turn, highlights the potential of generating copious micro-opto-electro-mechanical polymer structures for numerous sensing applications ranging from Lab-on-Chip to environmental applications using the presented hybrid micromachining approach. KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2020 U6 - https://doi.org/10.1016/j.optlaseng.2020.106362 VL - 137 IS - 10362 SP - 1 EP - 8 ER - TY - JOUR A1 - Kefer, Stefan A1 - Sauer, Theresia A1 - Hessler, Steffen A1 - Kaloudis, Michael A1 - Hellmann, Ralf T1 - Microstructure-Based Fiber-to-Chip Coupling of Polymer Planar Bragg Gratings for Harsh Environment Applications JF - Sensors (Basel) N2 - This article proposes and demonstrates a robust microstructure-based fiber-to-chip coupling scheme for planar Bragg grating devices. A polymer planar Bragg grating substrate is manufactured and microstructured by means of a micromilling process, while the respective photonic structures are generated by employing a sophisticated single-writing UV-exposure method. A stripped standard single mode fiber is inserted into the microstructure, which is filled with a UV-curable adhesive, and aligned with the integrated waveguide. After curing, final sensor assembly and thermal treatment, the proposed coupling scheme is capable of withstanding pressures up to 10 bar, at room temperature, and pressures up to 7.5 bar at an elevated temperature of 120 °C. Additionally, the coupling scheme is exceedingly robust towards tensile forces, limited only by the tensile strength of the employed single mode fiber. Due to its outstanding robustness, the coupling scheme enables the application of planar Bragg grating devices in harsh environments. This fact is underlined by integrating a microstructure-coupled photonic device into the center of a commercial-grade carbon fiber-reinforced polymer specimen. After its integration, the polymer-based Bragg grating sensor still exhibits a reflection peak with a dynamic range of 24 dB, and can thus be employed for sensing purposes. KW - Bragg grating sensors KW - cyclic olefin copolymers KW - fiber-to-chip coupling KW - microstructures KW - micromilling Y1 - 2020 UR - https://www.mdpi.com/1424-8220/20/19/5452/htm U6 - https://doi.org/10.3390/s20195452 VL - 20 IS - 19 SP - 5452 EP - 5452 ER -