@article{KeferPapeBischoffetal.2024, author = {Kefer, Stefan and Pape, Natalie and Bischoff, Kay and Schmauss, Bernhard and Hellmann, Ralf}, title = {Lattice-Like Waveguides With Integrated Bragg Gratings in Planar Cyclic Olefin Copolymers}, series = {Journal of Lightwave Technology}, volume = {42}, journal = {Journal of Lightwave Technology}, number = {18}, publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, issn = {0733-8724}, doi = {10.1109/JLT.2023.3328323}, pages = {6302 -- 6311}, year = {2024}, abstract = {This contribution demonstrates femtosecond laser direct writing of lattice-like waveguides in planar cyclic olefin copolymer substrates. Based on numerical simulation and experimental near-field analysis, stable single-mode waveguiding around wavelengths of 1550 nm is demonstrated. The waveguiding mechanism is based on a hexagonal array of laser-induced, positive refractive index modification lines. Thus, the lateral extension of the guided mode can be adapted by varying the fabrication parameters and, in consequence, the resulting cross-sectional arrangement of the refractive index perturbations. With an optical attenuationof 2.2 dB·cm-1 around 1550 nm, the fabricated waveguides are well-suited for on-chip integrated photonic devices. Moreover, the waveguides can also be equipped with Bragg gratings to enable the application of the photonic platform as a sensing device. Dependingon their length, the Bragg grating structures exhibit reflectivities ofup to 99\% and spectral widths down to 0.3 nm. The flexibility of the fabrication process and the sensing capabilities of the lattice-like waveguides with integrated Bragg gratings are underlined by an exemplary application study demonstrating a relative pressure sensor. For that, a photonic platform is micromilled to generate a 300 µm thick diaphragm and a reference pressure chamber. The strain introduced to the diaphragm by external pressure changes can then be quantified by the integrated photonic structures.This way, absolute pressure sensitivities of up to 38 pm·kPa-1 can be achieved in a relative pressure range from -60 to 100 kPa. The newly-developed lattice-like waveguides with integrated Bragggratings are therefore well-suited for the realization of novel and adaptable photonic devices and sensors.}, subject = {Wellenleiter}, language = {en} } @article{HaefnerBischoffHelmetal.2023, author = {H{\"a}fner, Tom and Bischoff, Kay and Helm, Jonas and Kunz, Tim and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {Picosecond laser microvia drilling of ABF material using MHz burst mode}, series = {Materials Research Express}, volume = {10}, journal = {Materials Research Express}, number = {9}, pages = {096301 -- 096311}, year = {2023}, abstract = {We report on a comprehensive study of laser percussion microvia drilling of Ajinomoto build-up film (ABF) material using an ultrashort pulsed laser in MHz burst mode. After laser processing, microvia drilling quality is being evaluated by the fabricated diameter and taper using laser scanning microscopy and metallography. The influences of the incubation effect, heat accumulation and shielding effects as a result of pulse to pulse interactions are being discussed on the ablation threshold, penetration depth and laser microvia drilling quality. We find that an increasing heat accumulation in MHz burst mode processing is responsible for the void formation and delamination of the insulating ABF layer. Therefore, the parameter clearance is introduced to evaluate these effects on the microvia sidewalls. For a comparable clearance, applying 2 intra-burst pulses achieves an average reduced taper of down to 19.5\% compared to single pulse mode. At the same time, a reduced laser drilling time of 16.7\% per microvia highlights the enormous potential of the MHz burst mode for laser drilling of ABF material in printed circuit board fabrication.}, subject = {Ultrakurzzeitlaser}, language = {en} } @inproceedings{BischoffKeferEsenetal.2024, author = {Bischoff, Kay and Kefer, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {Towards entirely ultrashort pulsed laser based process chain to manufacture polymer lab-on-chip systems with electrical, photonic, and microfluidic functionalities}, series = {The 5th Smart Laser Processing Conference (SLPC)}, booktitle = {The 5th Smart Laser Processing Conference (SLPC)}, year = {2024}, subject = {Ultrakurzzeitlaser}, language = {de} } @article{BischoffEsenHellmann2024, author = {Bischoff, Kay and Esen, Cemal and Hellmann, Ralf}, title = {Femtosecond reductive Laser Sintering under multiple focus conditions for rapid production of conductive copper layers}, series = {Procedia CIRP}, volume = {124}, journal = {Procedia CIRP}, number = {124}, publisher = {Elsevier BV}, issn = {2212-8271}, doi = {10.1016/j.procir.2024.08.189}, pages = {629 -- 633}, year = {2024}, abstract = {Reductive laser sintering is an advantageous alternative to conventional precious metal- or mask-based processes for the electrification of polymers and has been demonstrated in a variety of sensor applications. Ultrashort pulsed lasers promise precise control of the energy applied during sintering and ablation. Besides fine tracks, microelectronic circuits include wide contact pads, which leads to time-consuming processing with small laser spot sizes. The use of larger focal diameters, which results in wider lines and thus a higher metallization rate, is accompanied by a loss of structure resolution. We show the influence of focusing on the femtosecond reductive laser sintering of copper(II) oxide on cyclic olefin copolymers. While small focus diameters down to 23 µm provide high accuracy, increasing the laser power and the focus diameter up to 400 µm significantly accelerates the process, first by enlarging the line width and second by increasing the scanning speed due to the exposure time. Two-dimensional copper electrodes for 23 µm and 200 µm focal diameters were generated by hatching individual lines and compared with respect to their morphology. The enlarged spot can be used for high-speed generation of electrodes with a surface conductivity of 117 mΩ/sq. Hybrid processes with production under combined focusing conditions are presented for the first time.}, subject = {Laserstrahlsintern}, language = {en} }