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    <title language="eng">Optimization of Heat Accumulation during Femtosecond Laser Drilling Borehole Matrices by Using a Simplex Algorithm</title>
    <abstract language="eng">We report on an optimization study of percussion drilling thin metal sheets employing a high repetition rate, high power femtosecond laser with respect to the resulting heat accumulation. A specified simplex algorithm was employed to optimize the spatial drilling sequence, whereas a simplified thermal simulation using COMSOL was validated by comparing its results to the temperature measurements using an infrared camera. Optimization for drilling borehole matrices was aspired with respect to the generated temperature across the processed specimen, while the drilling strategy was altered in its spatial drilling sequence and by using multi-spot approaches generated by a spatial light modulator. As a result, we found that an optimization strategy based on limited consecutive holes in a Moore neighborhood led to reduced temperatures and the shortest process times.</abstract>
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    <enrichment key="HAB_Review">ja</enrichment>
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    <author>Kay Bischoff</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserstrahlsintern</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>2249</id>
    <completedYear>2023</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>2693</pageFirst>
    <pageLast>2693</pageLast>
    <pageNumber/>
    <edition/>
    <issue>19</issue>
    <volume>13</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2023-10-02</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Preparation of Dispersed Copper(II) Oxide Nanosuspensions as Precursor for Femtosecond Reductive Laser Sintering by High-Energy Ball Milling</title>
    <abstract language="eng">This contribution demonstrates and discusses the preparation of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS). Since the presence of agglomerates interferes with the various RLS sub-processes, fine dispersion is required, and oversized particles must be identified by a measurement methodology. Aside from the established method of scanning electron microscopy for imaging individual dried particles, this work applies the holistic and statistically more significant laser diffraction in combination with dynamic image analysis in wet dispersion. In addition to direct ultrasonic homogenization, high-energy ball milling is introduced for RLS, to produce stable nanosuspensions with a high fine fraction, and, above all, the absence of oversize particles. Whereas ultrasonic dispersion stagnates at particle sizes between 500 nm and 20 μm, even after 8 h, milled suspension contains a high proportion of finest particles with diameters below 100 nm, no agglomerates larger than 1 μm and a trimodal particle size distribution with the median at 50 nm already, after 100 min of milling. The precursor layers produced by doctor blade coating are examined for their quality by laser scanning microscopy. The surface roughness of such a dry film can be reduced from 1.26 μm to 88 nm by milling. Finally, the novel precursor is used for femtosecond RLS, to produce homogeneous, high-quality copper layers with a sheet resistance of 0.28 Ω/sq and a copper mass concentration of 94.2%.</abstract>
    <parentTitle language="eng">Nanomaterials</parentTitle>
    <identifier type="doi">https://doi.org/10.3390/nano13192693</identifier>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="HAB_Review">ja</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">false</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Kay Bischoff</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserstrahlsintern</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>2247</id>
    <completedYear>2022</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>2962</pageFirst>
    <pageLast>2962</pageLast>
    <pageNumber/>
    <edition/>
    <issue>14</issue>
    <volume>14</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2022-07-21</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">UV-Femtosecond-Laser Structuring of Cyclic Olefin Copolymer</title>
    <abstract language="eng">We report on the laser ablation of cyclic olefin copolymer using an amplified ultrashort pulsed laser in the ultraviolet spectral range. In addition to a high ablation depth per laser-structured layer up to 74 μm at a fluence of 22 J cm−2, an excellent mean roughness 𝑅𝑎&#13;
 of laser-patterned surfaces down to 0.5 μm is demonstrated. Furthermore, with increasing fluence, increasing ablation efficiencies up to 2.5 mm3 W−1 min−1 are determined. Regarding the quality of the ablation, we observed steep ablation flanks and low debris formation, though for fluences above 10.5 J cm−2 the formation of troughs was observed, being attributed to multiple reflections on the ablation flanks. For comparison, laser ablation was performed under identical conditions with an infrared laser wavelength. The results highlight that UV ablation exhibits significant advantages in terms of ablation efficiency, surface roughness and quality. Moreover, our results show that a larger UV focus spot accelerates the ablation process with comparable quality, paving the way for high-power UV ultrashort pulsed lasers towards an efficient and qualitative tool for the laser machining of cyclic olefin copolymer. The production of complex microfluidics further underlines the suitability of this type of laser.</abstract>
    <parentTitle language="eng">Polymers</parentTitle>
    <identifier type="doi">https://doi.org/10.3390/polym14142962</identifier>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="HAB_Review">ja</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Kay Bischoff</author>
    <author>Dominik Mücke</author>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>2082</id>
    <completedYear>2022</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>6233</pageFirst>
    <pageLast>6233</pageLast>
    <pageNumber/>
    <edition/>
    <issue>18</issue>
    <volume>15</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2022-09-08</completedDate>
    <publishedDate>2022-09-08</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces</title>
    <abstract language="eng">Sapphire is a robust and wear-resistant material. However, efficient and high-quality micromachining is still a challenge. This contribution demonstrates and discusses two novels, previously unreported approaches for femtosecond laser-based micromachining of rotational-symmetric sapphire workpieces, whereas both methods are in principal hybrids of laser scanning and laser turning or laser lathe. The first process, a combination of a sequential linear hatch pattern in parallel to the workpiece’s main axis with a defined incremental workpiece rotation, enables the fabrication of sapphire fibers with diameters of 50 µm over a length of 4.5 mm. Furthermore, sapphire specimens with a diameter of 25 µm over a length of 2 mm can be fabricated whereas an arithmetical mean height, i.e., Sa parameter, of 281 nm is achieved. The second process combines a constant workpiece feed and orthogonal scanning with incremental workpiece rotation. With this approach, workpiece length limitations of the first process are overcome and sapphire fibers with an average diameter of 90 µm over a length of 20 cm are manufactured. Again, the sapphire specimen exhibits a comparable surface roughness with an average Sa value of 249 nm over 20 cm. Based on the obtained results, the proposed manufacturing method paves an innovative and flexible, all laser-based way towards the fabrication or microstructuring of sapphire optical devices, and thus, a promising alternative to chemical processes.</abstract>
    <parentTitle language="eng">Materials</parentTitle>
    <identifier type="url">https://www.mdpi.com/1996-1944/15/18/6233</identifier>
    <identifier type="doi">10.3390/ ma15186233</identifier>
    <enrichment key="copyright">1</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">false</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Stefan Kefer</author>
    <author>Julian Zettl</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>sapphire</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>femtosecond laser</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>micromachining</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>laser turning</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>ablation threshold</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Saphir</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <file>https://opus4.kobv.de/opus4-h-ab/files/2082/Kefer2022_OPUS.pdf</file>
  </doc>
  <doc>
    <id>2043</id>
    <completedYear>2022</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>234</pageFirst>
    <pageLast>234</pageLast>
    <pageNumber/>
    <edition/>
    <issue>4</issue>
    <volume>9</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2022-04-01</completedDate>
    <publishedDate>2022-04-01</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Sapphire Photonic Crystal Waveguides with Integrated Bragg Grating Structure</title>
    <abstract language="eng">Abstract: This contribution demonstrates photonic crystal waveguides generated within bulk planar sapphire substrates. A femtosecond laser is used to modify the refractive index in a hexagonal pattern around the pristine waveguide core. Near-field measurements reveal single-mode behavior at a wavelength of 1550 nm and the possibility to adapt the mode-field diameter. Based on farfield examinations, the effective refractive index contrast between the pristine waveguide core and depressed cladding is estimated to 3x10-4. Additionally, Bragg gratings are generated within the waveguide core. Due to the inherent birefringence of Al2O3, the gratings exhibit two distinct wavelengths of main reflection. Each reflection peak exhibits a narrow spectral full width at a half maximum of 130 pm and can be selectively addressed by exciting the birefringent waveguide with appropriately polarized light. Furthermore, a waveguide attenuation of 1 dB cm-1 is determined.</abstract>
    <parentTitle language="eng">Photonics</parentTitle>
    <identifier type="url">https://www.mdpi.com/2304-6732/9/4/234</identifier>
    <identifier type="doi">https://doi.org/10.3390/photonics9040234</identifier>
    <enrichment key="copyright">1</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Stefan Kefer</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>integrated photonics</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>sapphire</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Bragg grating</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>femtosecond laser</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>photonic crystal waveguide</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Wellenleiter</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Bragg-Reflektor</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
    <file>https://opus4.kobv.de/opus4-h-ab/files/2043/Kefer2022_Sapphire_Photonic_Crystal_Waveguides.pdf</file>
  </doc>
  <doc>
    <id>1933</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1562</pageFirst>
    <pageLast>1568</pageLast>
    <pageNumber/>
    <edition/>
    <issue>68</issue>
    <volume>2021</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-07-07</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Laser turning with ultrashort laser pulses</title>
    <abstract language="eng">We report on a comprehensive micromachining study of rotationally symmetric parts using femtosecond laser. A&#13;
laser turning process with tangential impingement of the laser radiation complemented by a trepanning optics is&#13;
implemented as to accomplish a true laser lathe micromachining approach. With the objective of optimized&#13;
ablation rate and reduced surface roughness, the influence of pulse energy, feed rate, trepanning diameter and&#13;
angular beam incidence, respectively, is investigated for processing stellite rods. We find the smallest feasible&#13;
feature sizes of 8.5 μm in diameter and smoothest surfaces with an arithmetic average of the roughness profile as&#13;
low as 0.18 μm. The surface roughness, however, appears to be limited by the occurrence of laser induced periodic&#13;
surface structures provoked by the femtosecond laser radiation. Furthermore, the variation of the fluence&#13;
in accordance to the incidence on a curved surface is discussed and the heat input into the material is examined&#13;
through a longitudinal cross section.</abstract>
    <parentTitle language="eng">Journal of Manufacturing Processes</parentTitle>
    <identifier type="doi">10.1016/j.jmapro.2021.06.025</identifier>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Julian Zettl</author>
    <author>Maximilian Klar</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrashort laser pulses</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Turning</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ablation rate</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Tangential processing</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Trepanning optic</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Ultrakurzer Lichtimpuls</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserbearbeitung</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Mikrobearbeitung</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1925</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>23477</pageFirst>
    <pageLast>23486</pageLast>
    <pageNumber/>
    <edition/>
    <issue>15</issue>
    <volume>29</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-07-19</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Ultrashort pulsed laser backside ablation of fused silica</title>
    <parentTitle language="deu">Optics Express</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Quarzglas</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Mikrobearbeitung</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>1924</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1018</pageFirst>
    <pageLast>1018</pageLast>
    <pageNumber/>
    <edition/>
    <issue>11</issue>
    <volume>2021</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-01-23</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Compact Beam Homogenizer Module with Laser-Fabricated Lens-Arrays</title>
    <parentTitle language="eng">applied sciences</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Babette Götzendorfer</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Linse</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Array</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1923</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>282</pageFirst>
    <pageLast>285</pageLast>
    <pageNumber/>
    <edition/>
    <issue>2</issue>
    <volume>46</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-01-15</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Enhanced ablation efficiency using GHz bursts in micromachining fused silica</title>
    <parentTitle language="eng">Optics Letters</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Fräsen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Mikrobearbeitung</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Quarzglas</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1891</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>2002203</pageFirst>
    <pageLast>2002203</pageLast>
    <pageNumber/>
    <edition/>
    <issue>13</issue>
    <volume>9</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-04-07</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles</title>
    <abstract language="eng">This contribution demonstrates and discusses electrically tunable polymer planar Bragg gratings based on bulk cyclic olefin copolymers. A lithographic single-writing-step method and femtosecond laser reductive sintering of copper(II) oxide nanoparticles are subsequently employed in order to generate buried photonic structures and copper conducting paths on top of the polymer substrate. This way, the necessary number of process steps for fabricating a planar polymer-based electro-optical device is greatly reduced. The response of a fully electrified grating structure follows temperature changes, induced by the copper conducting path, with sensitivities up to −31 pm K−1. Dilatometric measurements show that the specimen's behavior is correlated to the situationally reduced thermal expansion of the bulk polymer substrate. In consequence, the tuning response of the photonic platform follows a second order polynomial, whereas a direct current of 30 mA, which correlates to a power consumption of 18.3 mW, leads to a local temperature increase and a residual Bragg wavelength shift of 19.6 K and −547 pm, respectively. Moreover, the outstanding flexibility of the proposed fabrication concept is underlined by demonstrating alternative conducting path geometries, whereas one of the additional designs is adapted to control the spectral width of the Bragg grating's reflection peak.</abstract>
    <parentTitle language="eng">Advanced Optical Materials</parentTitle>
    <identifier type="url">https://onlinelibrary.wiley.com/doi/10.1002/adom.202002203</identifier>
    <identifier type="doi">https://doi.org/10.1002/adom.202002203</identifier>
    <enrichment key="copyright">1</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Stefan Kefer</author>
    <author>Kay Bischoff</author>
    <author>Gian-Luca Roth</author>
    <author>Julian Haubner</author>
    <author>Bernhard Schmauss</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Bragg gratings</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>CuO nanoparticles</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>cyclic olefin copolymers</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>electro-optic tuning</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>integrated photonics</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Bragg-Reflektor</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
    <file>https://opus4.kobv.de/opus4-h-ab/files/1891/ADOM_OPUS.pdf</file>
  </doc>
  <doc>
    <id>1765</id>
    <completedYear>2021</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>6</pageLast>
    <pageNumber/>
    <edition/>
    <issue>1</issue>
    <volume>16</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2021-02-03</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Integration of Microfluidic and Photonic Components within Transparent Cyclic Olefin Copolymers by Using fs Laser</title>
    <abstract language="eng">In this study, we report on the integration of microfluidic channels and optical components by focusing femtosecond laser radiation inside transparent cyclic olefin copolymer (COC) bulk material. An internal localized material modification is triggered based on nonlinear absorption of the laser radiation's high intensities inside the focal volume. The size and shape of the three-dimensional internal modification are controlled by using an adaptive beam shaping setup. The irradiated areas show a positive refractive index shift and can be used as Type I internal optical waveguides. Furthermore, precise control of the spatial pulse-to-pulse distance in combination with a suitable beam profile enables the integration of functional photonic elements, e.g., Bragg gratings, into the waveguide. Thus, it also enables the generation of integrated photonic sensors. In addition, internal fs laser-induced modifications are characterized by a lower thermal stability as compared to the pristine polymer material. By performing a post-annealing process step, internal hollow microstructures are created by gaseous degradation of the exposed areas. Circular microchannels can be generated in a deliberately chosen layout by employing motorized 3D stages. In comparison to etching-based fabrication methods the proposed technology facilitates unlimited channel lengths, as it omits restrictions arising from an etching selectivity and duration. Altogether, this contribution paves the way towards the fabrication of internal three-dimensional optofluidic devices, equipped with a photonic sensor. In contrast, microfluidic and photonic structures are both created by femtosecond laser direct writing inside of transparent polymers.</abstract>
    <parentTitle language="eng">Journal of Laser Micro/Nanoengineering</parentTitle>
    <identifier type="doi">10.2961/jlmn.2021.01.2009</identifier>
    <enrichment key="copyright">1</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Stefan Kefer</author>
    <author>Steffen Hessler</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1688</id>
    <completedYear>2020</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>8</pageLast>
    <pageNumber/>
    <edition/>
    <issue>10362</issue>
    <volume>137</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2020-08-27</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Fs-laser based hybrid micromachining for polymer micro-opto electrical systems</title>
    <abstract language="eng">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.</abstract>
    <parentTitle language="eng">Optics and Lasers in Engineering</parentTitle>
    <identifier type="doi">10.1016/j.optlaseng.2020.106362</identifier>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Julian Haubner</author>
    <author>Stefan Kefer</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Bragg-Reflektor</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1687</id>
    <completedYear>2020</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>18077</pageFirst>
    <pageLast>18084</pageLast>
    <pageNumber/>
    <edition/>
    <issue>12</issue>
    <volume>28</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2020-06-08</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Femtosecond laser inscription of waveguides and Bragg gratings in transparent cyclic olefin copolymers</title>
    <abstract language="eng">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.</abstract>
    <parentTitle language="eng">Optics Express</parentTitle>
    <identifier type="doi">10.1364/OE.388364</identifier>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Steffen Hessler</author>
    <author>Stefan Kefer</author>
    <author>Maiko Girschikofsky</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Wellenleiter</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Bragg-Reflektor</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1667</id>
    <completedYear>2020</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>032017-1</pageFirst>
    <pageLast>032017-6</pageLast>
    <pageNumber/>
    <edition/>
    <issue>3</issue>
    <volume>32</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2020-07-02</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Influence of laser wavelength on the modification of friction between 100Cr6 steel and polytetrafluoroethylene by femtosecond laser-induced periodic surface structures</title>
    <parentTitle language="eng">Journal of Laser Applications</parentTitle>
    <identifier type="doi">10.2351/7.0000036</identifier>
    <enrichment key="copyright">1</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>Stefan Rung</author>
    <author>Kevin Bokan</author>
    <author>Simon Schwarz</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1593</id>
    <completedYear>2017</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>67</pageFirst>
    <pageLast>71</pageLast>
    <pageNumber/>
    <edition/>
    <issue>2</issue>
    <volume>12</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2017-09-01</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Two-Dimensional Low Spatial Frequency Laser-Induced Periodic Surface Structuring of Sapphire</title>
    <parentTitle language="eng">Journal of Laser Micro/Nanoengineering</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1591</id>
    <completedYear>2018</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1624</pageFirst>
    <pageLast>1624</pageLast>
    <pageNumber/>
    <edition/>
    <issue>9</issue>
    <volume>8</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2018-09-12</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Surface Plasmon Polariton Triggered Generation of 1D-Low Spatial Frequency LIPSS on Fused Silica</title>
    <parentTitle language="eng">Applied Sciences</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Quarzglas</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1590</id>
    <completedYear>2020</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>012001</pageFirst>
    <pageLast>012001</pageLast>
    <pageNumber/>
    <edition/>
    <issue>1</issue>
    <volume>32</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2020-02-16</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Rapid fabrication of precise glass axicon arrays by an all laser-based manufacturing technology</title>
    <parentTitle language="eng">Journal of Laser Applications</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>1589</id>
    <completedYear>2018</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>90</pageFirst>
    <pageLast>94</pageLast>
    <pageNumber/>
    <edition/>
    <issue>2</issue>
    <volume>13</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2018-09-01</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Homogeneous low spatial frequency LIPSS on dielectric materials generated by beam-shaped femtosecond pulsed laser irradiation</title>
    <parentTitle language="eng">Journal of Laser Micro/Nanoengineering</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1577</id>
    <completedYear>2019</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>49</pageFirst>
    <pageLast>53</pageLast>
    <pageNumber/>
    <edition/>
    <issue>1</issue>
    <volume>14</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2019-04-01</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">A New Approach to Seal Polymer Microfluidic Devices Using Ultrashort Laser Pulses</title>
    <abstract language="eng">We report on the joining of two different transparent thermoplastic polymers using infrared femtosecond laser pulses. Solely being based on nonlinear absorption, the developed micro-welding process for cyclo-olefin copolymers and polycarbonate does not require any intermediate absorbing layers or any surface pre-processing of the welding partners. In addition, it circumvents any heat damages at the outer surfaces of the welding partners. Femtosecond laser welding of cyclo-olefin copolymers is improved by increasing the numerical aperture of the focusing setup resulting in a wider and more homogenous welding cross-section. Welding results are classified by shear strength and fracture modes are analyzed using scanning electron microscopy. Furthermore, we demonstrate, to the best of our knowledge, first results of ultrashort pulse laser welding of transparent polycarbonate, one of the most used transparent polymers. In view of an optimized and stable micro-welding process, we study the influence of laser power and focal position on welding results. The application of ultrashort pulse laser welding for Lab-on-chip fabrication technologies is demonstrated by sealing an ultrashort pulse laser ablated microfluidic device based on a transparent polymer substrate.</abstract>
    <parentTitle language="eng">Journal of Laser Micro/Nanoengineering</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserschweißen</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Business Transformation and Innovation Management</collection>
  </doc>
  <doc>
    <id>1576</id>
    <completedYear>2020</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>5801</pageFirst>
    <pageLast>5811</pageLast>
    <pageNumber/>
    <edition/>
    <issue>4</issue>
    <volume>28</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2020-02-18</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Microchannels inside bulk PMMA generated by femtosecond laser using adaptive beam shaping</title>
    <abstract language="eng">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.</abstract>
    <parentTitle language="eng">Optics Express</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Polymethylmethacrylate</value>
    </subject>
    <collection role="institutes" number="">Angewandte Lasertechnik und Photonik (alp)</collection>
    <collection role="institutes" number="">ZeWiS</collection>
  </doc>
  <doc>
    <id>1574</id>
    <completedYear>2018</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>155</pageFirst>
    <pageLast>159</pageLast>
    <pageNumber/>
    <edition/>
    <issue>3</issue>
    <volume>13</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2018-01-12</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Vertical Microchannels for Microfluidic Multilayer Interconnections in PMMA</title>
    <abstract language="eng">We report on laser generation of microchannels by focused femtosecond laser pulses inside PMMA bulk material. This process enables direct fabrication of three dimensional microfluidic channel architectures with generally unlimited channel length. Based on nonlinear ultrashort pulse laser absorption of high intensities around the focal volume, a material modification including a refractive index shift is triggered. After laser exposure the channel is created by a gaseous degradation of exposed areas during an annealing process. The 3D channel layout can easily be realized by moving the specimen using 3D motorized stages, allowing freely chosen complex shaped channel architectures. In this report, the creation of inner lying vertical microchannels is examined. In addition to previously shown horizontal channel architectures vertical channels are necessary to fulfill the definition of an internal three-dimensional microfluidic structure and to create interconnections in multilevel lab on chip devices. The cross section and geometry of vertical channels are strongly influenced by laser parameters such as pulse duration, laser power and writing speed. The influence of these process parameters on the channels diameter is determined and parameters are optimized regarding a controllable, stable and reproducible process. The functionality of vertical microchannels as an interconnection between multilayer microfluidic devices is demonstrated using a Rhodamine B solution.</abstract>
    <parentTitle language="eng">Journal of Laser Micro/Nanoengineering</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Polymethylmethacrylate</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1573</id>
    <completedYear>2019</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>022603-1</pageFirst>
    <pageLast>022603-5</pageLast>
    <pageNumber/>
    <edition/>
    <issue>2</issue>
    <volume>31</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2019-05-10</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Circular microchannels inside bulk polymethylmethacrylate generated by femtosecond laser using slit beam shaping</title>
    <abstract language="eng">The authors report on the laser generation of three-dimensional microchannel architectures with fundamentally unlimited channel length by focused 514 nm femtosecond laser pulses inside polymethylmethacrylate bulk material. The three-dimensional channel layout is implemented by moving the specimen using three-dimensional motorized stages, allowing freely chosen complex shaped channel architectures. Based on nonlinear absorption of high intensities around the focal volume, a material modification, including a refractive-index shift is triggered. After laser exposure, the channel is created by a gaseous degradation of exposed areas during an annealing process. Cross section and aspect ratio of thus generated microchannels are strongly influenced by the numerical aperture of the applied objective. To obtain a circular cross-sectional shape, high focusing objectives are necessary. In this report, the authors improve the existing setup by using an elliptical input beam, transforming the intensity distribution of the focal area in the propagation direction to a circular shape even for low and medium numerical aperture focusing objectives and therefore avoiding a small working distance as a limiting factor for processing depth. The elliptical input beam is obtained by insertion of a slit mask in front of the focusing objective. The ellipticity of the incident beam defines the aspect ratio of the generated microchannels. Furthermore, the size of internal microchannels is adjustable by varying laser and annealing process parameters.</abstract>
    <parentTitle language="eng">Journal of Laser Applications</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>1585</id>
    <completedYear>2018</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>23287</pageFirst>
    <pageLast>23294</pageLast>
    <pageNumber/>
    <edition/>
    <issue>18</issue>
    <volume>26</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2018-09-03</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Fabrication of a high-quality axicon by femtosecond laser ablation and CO2 laser polishing for quasi-Bessel beam generation</title>
    <parentTitle language="eng">Optics Express</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Simon Schwarz</author>
    <author>Stefan Rung</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
  </doc>
  <doc>
    <id>1570</id>
    <completedYear>2019</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>9</pageLast>
    <pageNumber/>
    <edition/>
    <issue>6</issue>
    <volume>5</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2019-02-25</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Towards a versatile point-of-care system combining femtosecond laser generated microfluidic channels and direct laser written microneedle arrays</title>
    <abstract language="eng">Microneedle-based microfluidic systems have a great potential to become well-accepted medical devices for simple, accurate, and painless drug delivery and lab-on-a-chip diagnostics. In this work, we report on a novel hybrid approach combining femtosecond direct laser written microneedles with femtosecond laser generated microfluidic channels providing an important step towards versatile medical point-of-care systems. Hollow microneedle arrays are fabricated by a laser system designed for two-photon polymerization applications. Compression tests of two different types of truncated cone-shaped microneedle arrays prepared from OrmoComp® give information about the microneedle mechanical strength, and the results are compared to skin insertion forces. Three-dimensional microchannels are directly created inside PMMA bulk material by an ultrashort pulse laser system with vertical channels having adjustable cross-sectional areas, which allow attaching of microneedles to the microfluidic system. A comprehensive parameter study varying pulse duration and repetition rate is performed on two-photon polymerization to identify an optimal laser power range for fabricating microneedles using the same pulse duration and repetition rate as for microchannels. This addresses the advantage of a single laser system process that overcomes complex fabrication methods. A proof of concept flow test with a rhodamine B dye solution in distilled water demonstrates that the combination of microneedles and microchannels qualifies for microfluidic injection and extraction applications.</abstract>
    <parentTitle language="eng">Microsystems &amp; Nanoengineering</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Anika Trautmann</author>
    <author>Gian-Luca Roth</author>
    <author>Benedikt Nujiqi</author>
    <author>Thomas Walter</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1571</id>
    <completedYear>2018</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>032016-1</pageFirst>
    <pageLast>032016-6</pageLast>
    <pageNumber/>
    <edition/>
    <issue>3</issue>
    <volume>30</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2018-08-08</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Control of femtosecond laser generated microfluidic channels inside poly (methyl methacrylate)</title>
    <abstract language="eng">In this study, the authors report on femtosecond laser direct generation of microchannels inside poly(methyl methacrylate) with variable dimensions ranging from a channel height of 20 to 350 μm and an aspect ratio down to 1.2. Focused ultrashort laser pulses are used to trigger a material modification in the focal area which can be selectively opened by a subsequent annealing process. A 3D microchannel architecture can easily be realized by moving the specimen using motorized stages, allowing freely chosen complex shaped channel layouts. While the laser wavelength is identified as one of the main parameters determining process effectiveness, another core of this study is the variation of channel dimensions by the numerical aperture of the applied objective to focus the laser. The authors find that both size and shape of the modified region and the resulting microchannel can be controlled by altering the numerical aperture.</abstract>
    <parentTitle language="eng">Journal of Laser Applications</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Polymethylmethacrylate</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1569</id>
    <completedYear>2017</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>178</pageFirst>
    <pageLast>181</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>93</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2017-01-06</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Ultrashort pulse laser micro-welding of cyclo-olefin copolymers</title>
    <abstract language="eng">We report on the joining of transparent thermoplastic polymers using infrared femtosecond laser pulses. Due to nonlinear absorption, the developed micro-welding process for cyclo-olefin copolymers does not require any intermediate absorbing layers or any surface pre-processing of the welding partners. In view of an optimized and stable micro-welding process, the influence of the welding speed and focal position on both, the quality and shear force strength are investigated. We highlight that welding seam widths of down to 65 µm are feasible for welding speeds of up to 75 mm/s. However, a variation of the welding speed affects the required focal position for a successful joining process. The shear force strength of the welding seam is determined to 37 MPa, which corresponds to 64% of the shear strength of the bulk material and is not affected by the welding speed.</abstract>
    <parentTitle language="eng">Optics and Lasers in Engineering</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Stefan Rung</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserschweißen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1567</id>
    <completedYear>2016</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>86</pageFirst>
    <pageLast>90</pageLast>
    <pageNumber/>
    <edition/>
    <issue>2</issue>
    <volume>122</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2016-01-03</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Welding of transparent polymers using femtosecond laser</title>
    <abstract language="eng">Based on nonlinear absorption, we report on laser welding of cycloolefin copolymers without any additional absorption layer employing infrared femtosecond laser. To the best of our knowledge, this is the first report of ultrashort laser welding of this material class, revealing a remarkable high processing speed of 20 mm/s in a single pass mode. Using a 1028 nm laser having a pulse duration of 220 fs at a repetition rate of 571 kHz leads to a welding seam width between 38 and 137 μm, depending on the applied laser average power. The welded joint is characterized by a maximum shear strength of 40 MPa. The experimental results are compared to those reported for femtosecond laser welding of PMMA and to those published for using a Thulium fiber laser.</abstract>
    <parentTitle language="eng">Applied Physics A</parentTitle>
    <enrichment key="copyright">1</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Stefan Rung</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Laserschweißen</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
  <doc>
    <id>1566</id>
    <completedYear>2017</completedYear>
    <publishedYear/>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>18442</pageFirst>
    <pageLast>18450</pageLast>
    <pageNumber/>
    <edition/>
    <issue>15</issue>
    <volume>25</volume>
    <type>article</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>2017-07-24</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Femtosecond laser direct generation of 3D-microfluidic channels inside bulk PMMA</title>
    <abstract language="eng">We report on laser direct generation of 3D-microchannels for microfluidic applications inside PMMA bulk material by focused femtosecond pulses. Inner lying channels with cross sectional areas from 100 µm2 to 4400 µm2 are directly created in the volume of a PMMA substrate. Using the presented process, the channel length is fundamentally unlimited. Here we demonstrate a channel length of 6 meters inside a substrate with dimensions of 20 × 20 × 1.1 mm. The formation of the micro channels is based on nonlinear absorption around the focal volume that triggers a material modification. The modified volume can be selectively opened to form the channel by a subsequent annealing process. The cross section of the channel is strongly influenced by the energy distribution and illumination around the focal volume determined by the optical setup and process design. The 3D channel layout can easily be realized by moving the specimen using 3D motorized stage, allowing freely chosen complex shaped channel architectures. Within a comprehensive parameter study, varying laser power, number of multi-passes, writing speed and writing depths, we identify an optimized process in terms of attainable channel height, width and aspect ratio, as well as process stability and reproducibility. The proof of concept for an application in three dimensional microfluidic systems is provided by florescence microscopy using a dye rhodamine B solution in isopropanol.</abstract>
    <parentTitle language="eng">Optics Express</parentTitle>
    <enrichment key="copyright">0</enrichment>
    <licence>Keine Lizenz - es gilt das deutsche Urheberrecht</licence>
    <author>Gian-Luca Roth</author>
    <author>Cemal Esen</author>
    <author>Ralf Hellmann</author>
    <subject>
      <language>deu</language>
      <type>swd</type>
      <value>Femtosekundenlaser</value>
    </subject>
    <collection role="forschungsschwerpunkte" number="">Intelligent Sensors and Signals</collection>
    <collection role="forschungsschwerpunkte" number="">Innovative Material Processing</collection>
    <collection role="forschungsschwerpunkte" number="">Material Testing &amp; Sensor Technology</collection>
  </doc>
</export-example>
