Dr. Henrik Ehlers Profile

Dr. Henrik Ehlers

Head of R&D at LASEROPTIK GmbH

SPIE Involvement:

Author

Publications (29)

Proceedings Article | 24 November 2023 Poster

Temperature and damage behavior of hybrid coated mirrors under continuous wave laser irradiation

Kevin Kiedrowski, Morten Steinecke, Henrik Ehlers, Michael Kennedy, Marco Jupé, Andreas Wienke, Detlev Ristau

Proceedings Volume PC12726, PC1272619 (2023) https://doi.org/10.1117/12.2685163

KEYWORDS: Mirrors, Oxides, Laser irradiation, Continuous wave operation, Laser scanners, Tantalum, Niobium, Multilayers, Metals, Manufacturing

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Proceedings Article | 3 December 2022 Poster + Presentation

Correlation of the damage behavior of high power continuous wave laser hybrid mirrors with total losses

Kevin Kiedrowski, Marco Jupé, Michael Kennedy, Henrik Ehlers, Andreas Wienke, Detlev Ristau

Proceedings Volume PC12300, PC123000D (2022) https://doi.org/10.1117/12.2642757

KEYWORDS: Mirrors, Continuous wave operation, High power lasers, Light scattering, Spectroscopes, Scattering, Reflectivity, Polarization, Manufacturing, Laser scanners

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Proceedings Article | 2 December 2022 Presentation + Paper

Comparison of high power sputtered dielectric mirrors for PW laser

T. Willemsen, T. Groß, M. Gauch, H. Ehlers, D. Kramer, P. Velpula, Wolfgang Ebert

Proceedings Volume 12300, 123000H (2022) https://doi.org/10.1117/12.2642134

KEYWORDS: Mirrors, Laser induced damage, Manufacturing, Optical coatings, Optics manufacturing, Dielectrics, Sputter deposition, Dielectric mirrors, Femtosecond lasers

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Proceedings Article | 25 May 2022 Presentation + Paper

High power laser-induced damage investigations of mirrors with several substrate materials in combination with heat transfer simulations

K. Kiedrowski, M. Jupé, M. Kennedy, H. Ehlers, A. Wienke, D. Ristau

Proceedings Volume 12142, 121420F (2022) https://doi.org/10.1117/12.2621132

KEYWORDS: Mirrors, Silica, Silicon carbide, Laser induced damage, Sapphire, Laser damage threshold

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Nowadays, continuous wave (cw) lasers have conquered a broad spectrum of applications in industrial laser processing and can be considered as the dominant tools in many manufacturing floors. This is reflected by the enormous average annual growth rates of 25-30 % and the continuous research efforts dedicated to this laser type leading to ever increasing output power and beam quality. This development imposes ever increasing demands on the quality of the optical laser components, that have to withstand the usually harsh industrial environment and high power levels. In fact, the corresponding of the laser components is a key factor for the efficiency and economic success of an employed laser material process. This in turn requires a thorough assessment of the quality parameters ruling the stability of such components. Among many other quality parameters, the Laser Induced Damage Threshold (LIDT) is one of the leading parameters that has to be investigated in detail. The corresponding measurement facilities and protocols as well as the evaluation of the data have to be performed with high reproducibility and comparability among different testing laboratories. As a consequence, such qualifications can only be achieved on the basis of well-defined international standards defining the complete procedure for the determination of LIDT values. We investigated the laser induced damage threshold of different types of optics using a cw laser with a wavelength of 1030 nm and power up to 6 kW, applying beam diameters of approximately 200-300 µm on the surface. The samples were irradiated for at least 30s or until damage occurred. First, it was necessary to review the existing DIN EN ISO 21254 regarding cw-irradiation of mirrors with a 25 mm diameter. An important aspect is the number of possible irradiation spots on each optic with respect to the damage size as well as the emitted debris. Both effects limit the statistical accuracy, the ISO procedure needs to be adapted to the measurement conditions. Additionally, we investigated the influence of substrate materials and coating processes on the LIDT of high reflective coatings and their damage behavior, especially regarding their thermal conductivity. The results were then compared with simulations concerning the maximum temperature within the optical component.

Proceedings Article | 12 October 2021 Presentation

Hybrid mirrors enabling storage-ring free-electron laser lasing below 170 nm

Leif Kochanneck, Henrik Ehlers, Stepan Mikhailov, Maurice Pentico, Ying K. Wu, Victor Popov, Patrick Wallace, Jun Yan, Lars Jensen

Proceedings Volume 11910, 119100W (2021) https://doi.org/10.1117/12.2600571

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Proceedings Article | 6 December 2016 Paper

Improved LIDT values for dielectric dispersive compensating mirrors applying ternary composites

T. Willemsen, S. Schlichting, M. Gyamfi, M. Jupé, H. Ehlers, U. Morgner, D. Ristau

Proceedings Volume 10014, 100141Z (2016) https://doi.org/10.1117/12.2244835

KEYWORDS: Composites, Mirrors, Dielectrics, Dielectric mirrors, Curium, Tantalum, Laser damage threshold, Reverse engineering, Laser induced damage, Detection and tracking algorithms

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Proceedings Article | 23 September 2015 Paper

Simulation in thin film technology

Marcus Turowski, Marco Jupé, Henrik Ehlers, Thomas Melzig, Andreas Pflug, Detlev Ristau

Proceedings Volume 9627, 962707 (2015) https://doi.org/10.1117/12.2191693

KEYWORDS: Monte Carlo methods, Coating, Thin films, Thin film growth, Computer simulations, Fused deposition modeling, Optical properties, Sputter deposition, Particles, Titanium dioxide

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Proceedings Article | 23 September 2015 Paper

Direct in situ GDD measurement in optical coating process

S. Schlichting, T. Willemsen, H. Ehlers, U. Morgner, D. Ristau

Proceedings Volume 9627, 96271S (2015) https://doi.org/10.1117/12.2191215

KEYWORDS: In situ metrology, Mirrors, Coating, Optical coatings, Spectroscopy, Light sources, Interferometry, Optical testing, Michelson interferometers, Algorithm development

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Proceedings Article | 23 September 2015 Paper

Properties of transparent organic-inorganic composite coatings prepared by ion beam sputtering of PTFE and Al2O3

Melanie Gauch, Henrik Ehlers, Detlev Ristau

Proceedings Volume 9627, 96270F (2015) https://doi.org/10.1117/12.2191067

KEYWORDS: Refractive index, Composites, Optical coatings, Ion beams, Sputter deposition, Oxygen, Fluorine, Absorption, FT-IR spectroscopy, Scattering

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Proceedings Article | 23 September 2015 Paper

Precise fabrication of ultra violet dielectric dispersion compensating mirrors

T. Willemsen, S. Schlichting, T. Kellermann, M. Jupé, H. Ehlers, U. Morgner, D. Ristau

Proceedings Volume 9627, 96271U (2015) https://doi.org/10.1117/12.2191051

KEYWORDS: Ultraviolet radiation, Mirrors, Near infrared, In situ metrology, Reflectivity, Dielectric dispersion, Dielectric mirrors, Spectroscopy, Solids, Silica

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Proceedings Article | 4 December 2012 Paper

Applying hafnia mixtures to enhance the laser-induced damage threshold of coatings for third-harmonic generation optics

Mathias Mende, Lars Jensen, Henrik Ehlers, Stefan Bruns, Michael Vergöhl, Peer Burdack, Detlev Ristau

Proceedings Volume 8530, 85300W (2012) https://doi.org/10.1117/12.971225

KEYWORDS: Thin films, Thin film coatings, Refractive index, Optical coatings, Annealing, Silica, Nonlinear crystals, Antireflective coatings, Laser induced damage, Laser damage threshold

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Proceedings Article | 29 November 2012 Paper

An exhaustive study of laser damage in ion beam sputtered pure and mixture oxide thin films at 1030 nm with 500 fs pulse durations

Laurent Gallais, Benoit Mangote, Mireille Commandré, Mathias Mende, Lars Jensen, Henrik Ehlers, Marco Jupé, Detlev Ristau, Andrius Melninkaitis, Valdas Sirutkaitis, Simonas Kičas, Tomas Tolenis, Ramutis Drazdys

Proceedings Volume 8530, 85300K (2012) https://doi.org/10.1117/12.977553

KEYWORDS: Silica, Oxides, Laser induced damage, Refractive index, Thin films, Ion beams, Laser damage threshold, Optical coatings, Zirconium dioxide, Thin film coatings

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Proceedings Article | 5 October 2011 Paper

Study of the laser matter interaction in the femtosecond regime: application to the analysis of the laser damage of optical thin films

B. Mangote, L. Gallais, M. Zerrad, M. Commandré, L. Gao, F. Lemarchand, M. Lequime, A. Melninkaitis, J. Mirauskas, V. Sirutkaitis, S. Kicas, T. Tolenis, R. Drazdys, M. Mende, L. Jensen, H. Ehlers, D. Ristau

Proceedings Volume 8168, 816815 (2011) https://doi.org/10.1117/12.897372

KEYWORDS: Laser induced damage, Refractive index, Laser damage threshold, Silica, Thin films, Oxides, Optical coatings, Femtosecond phenomena, Laser optics, Sputter deposition

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Proceedings Article | 4 October 2011 Paper

Laser-induced damage of pure and mixture material high reflectors for 355nm and 1064nm wavelength

Mathias Mende, Lars Jensen, Henrik Ehlers, Werner Riggers, Holger Blaschke, Detlev Ristau

Proceedings Volume 8168, 816821 (2011) https://doi.org/10.1117/12.897049

KEYWORDS: Reflectors, Silica, Multilayers, Refractive index, Absorption, Laser induced damage, Transmission electron microscopy, Ion beams, Hybrid fiber optics, Optical coatings

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High reflecting multilayer coatings play a key role for many applications of pulsed Nd:YAG high power lasers in industry and science. In the present contribution, improvements in the optical properties and the radiation resistance of high reflectors for 355nm and 1064nm wavelength on the basis of mixture materials are discussed. Within a co-operation between the LASEROPTIK GmbH and the Laser Zentrum Hannover e.V., several deposition processes including Ion Beam Sputtering, Magnetron Sputtering, and Electron Beam Evaporation could be addressed for this study. The selected material combinations HfO₂+ZrO₂/SiO₂, HfO₂+Al₂O₃/SiO₂, HfO₂+SiO₂/SiO₂ and HfO₂/SiO₂ were deposited using a zone target assembly for the IBS technique or defined material mixtures for the evaporation process. Single layers of the applied mixtures were analyzed by UV/Vis/NIR spectroscopy to correlate the optical constants with the atomic compositions quantified by Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS). In addition to pure material reference mirrors and reflecting multilayer coatings with high index material mixtures, also interference coatings consisting of nanolaminates as well as multilayer systems with refractive index profiles were produced. The laser induced damage thresholds at 1064nm wavelength for nanosecond pulse durations were measured in a 1000on1 experiment complying with the standard ISO11254. For the 355nm high reflectors, the radiation resistance was determined in a 10000on1 procedure, furthermore, the radiation-induced absorption was measured by laser calorimetry according to ISO11551. Finally, the layer interfaces and the amorphous microstructure of selected multilayers were analyzed by Transmission Electron Microscopy (TEM) to obtain detailed information about possible partial crystallinity. The results are interpreted in the context of former investigations on the power handling capability of coating systems involving material mixtures.

Proceedings Article | 4 October 2011 Paper

From independent thickness monitoring to adaptive manufacturing: advanced deposition control of complex optical coatings

Henrik Ehlers, Sebastian Schlichting, Carsten Schmitz, Detlev Ristau

Proceedings Volume 8168, 81681F (2011) https://doi.org/10.1117/12.898598

KEYWORDS: Optics manufacturing, Crystals, Manufacturing, Transmittance, Quartz, Crystal optics, Coating, Optical coatings, Process control, Titanium dioxide

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Proceedings Article | 4 October 2011 Paper

Online re-optimization as a powerful part of enhanced strategies in optical broadband monitoring

S. Schlichting, K. Heinrich, H. Ehlers, D. Ristau

Proceedings Volume 8168, 81681E (2011) https://doi.org/10.1117/12.898557

KEYWORDS: Coating, Transmittance, Computer simulations, Multilayers, Detection and tracking algorithms, Algorithm development, Virtual reality, Process control, Optics manufacturing, Titanium dioxide

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Proceedings Article | 4 October 2011 Paper

Optical and mechanical properties of oxide UV coatings, prepared by PVD techniques

Olaf Stenzel, Mark Schürmann, Steffen Wilbrandt, Norbert Kaiser, Andreas Tünnermann, Mathias Mende, Henrik Ehlers, Detlev Ristau, Stefan Bruns, Michael Vergöhl, Werner Riggers, Martin Bischoff, Mario Held

Proceedings Volume 8168, 81681W (2011) https://doi.org/10.1117/12.896775

KEYWORDS: Coating, Ultraviolet radiation, Oxides, Refractive index, Silicon, Thin films, Glasses, Temperature metrology, Silica, Semiconducting wafers

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Proceedings Article | 22 April 2009 Paper

Long term tests of resonator optics in ArF excimer lasers

Nils Beermann, Holger Blaschke, Henrik Ehlers, Detlev Ristau, Dirk Wulff-Molder, Sigrid Jukresch, Ansgar Matern, Martin Bischoff, Dieter Gäbler, Norbert Kaiser

Proceedings Volume 7131, 713117 (2009) https://doi.org/10.1117/12.816706

KEYWORDS: Resonators, Reflectors, Contamination, Excimer lasers, Laser optics, Optical coatings, Crystals, Interfaces, Laser resonators, Mirrors

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Proceedings Article | 30 December 2008 Paper

Investigation in the degradation of CaF2 outcouplers in excimer lasers operating at 193nm

H. Blaschke, N. Beermann, H. Ehlers, D. Ristau, M. Bischoff, D. Gäbler, N. Kaiser, A. Matern, D. Wulff-Molder

Proceedings Volume 7132, 71321A (2008) https://doi.org/10.1117/12.804428

KEYWORDS: Excimer lasers, Coating, Reflectors, Transmittance, Crystals, Ions, Interfaces, Electron microscopy, Reflectivity, Carbonates

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Proceedings Article | 25 September 2008 Paper

Reliable production of steep edge interference filters

Marc Lappschies, Peter Pfeifer, Uwe Schallenberg, Henrik Ehlers, Detlev Ristau

Proceedings Volume 7101, 71010P (2008) https://doi.org/10.1117/12.797459

KEYWORDS: Transmittance, Coating, Linear filtering, Interference filters, Optical filters, Spectroscopy, Refractive index, Sensors, Ions, Deposition processes

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Proceedings Article | 25 September 2008 Paper

A method for the determination of substrate temperature during thin film coating deposition

St. Günster, H. Ehlers, D. Ristau

Proceedings Volume 7101, 71010F (2008) https://doi.org/10.1117/12.797764

KEYWORDS: Optical coatings, Temperature metrology, Glasses, Transmittance, Vacuum ultraviolet, Absorption, Deposition processes, Silicon, Quartz, Thin film coatings

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Proceedings Article | 25 September 2008 Paper

State of the art in deterministic production of optical thin films

D. Ristau, H. Ehlers, S. Schlichting, M. Lappschies

Proceedings Volume 7101, 71010C (2008) https://doi.org/10.1117/12.797264

KEYWORDS: Optical coatings, Deposition processes, Optical filters, Crystals, Control systems, Refractive index, Switching, Sputter deposition, Quartz, Detection and tracking algorithms

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Proceedings Article | 25 September 2008 Paper

Optimization and characterization of transparent photocatalytic TiO2 thin films prepared by ion-assisted deposition

Redouan Boughaled, Sebastian Schlichting, Henrik Ehlers, Detlev Ristau, Inga Bannat, Michael Wark

Proceedings Volume 7101, 71010K (2008) https://doi.org/10.1117/12.797719

KEYWORDS: Ions, Thin films, Optical coatings, Ultraviolet radiation, Thin film coatings, Crystals, Oxygen, Image processing, Deposition processes, Titanium dioxide

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Proceedings Article | 15 January 2007 Paper

Damage threshold investigations of high-power laser optics under atmospheric and vacuum conditions

L. Jensen, M. Jupé, H. Mädebach, H. Ehlers, K. Starke, D. Ristau, W. Riede, P. Allenspacher, H. Schroeder

Proceedings Volume 6403, 64030U (2007) https://doi.org/10.1117/12.696443

KEYWORDS: Coating, Laser damage threshold, Antireflective coatings, Atmospheric optics, Tantalum, Dielectrics, Transmittance, Laser optics, Aerospace engineering, Ions

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Proceedings Article | 5 October 2005 Paper

Ion source characterization based on an array of retarding field analyzers

N. Beermann, H. Ehlers, D. Ristau

Proceedings Volume 5963, 59630H (2005) https://doi.org/10.1117/12.625215

KEYWORDS: Ions, Resolution enhancement technologies, Plasma, Coating, 3D metrology, Data centers, Optical coatings, Deposition processes, Energy efficiency, Silica

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Proceedings Article | 25 February 2004 Paper

Broadband optical monitoring for the deposition of complex coatings

Marc Lappschies, Tobias Gross, Henrik Ehlers, Detlev Ristau

Proceedings Volume 5250, (2004) https://doi.org/10.1117/12.514800

KEYWORDS: Transmittance, Optical coatings, Thin films, Refractive index, Data modeling, Thin film coatings, Deposition processes, Computer simulations, Detection and tracking algorithms, Computing systems

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Proceedings Article | 25 February 2004 Paper

Ion-assisted deposition processes for precision and laser optics

Henrik Ehlers, Tobias Gross, Marc Lappschies, Detlev Ristau

Proceedings Volume 5250, (2004) https://doi.org/10.1117/12.514811

KEYWORDS: Transmittance, Optical coatings, Ions, Deposition processes, Thin film coatings, Absorption, In situ metrology, Process control, Tantalum, Quartz

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Proceedings Article | 25 February 2004 Paper

Ion-assisted deposition processes: industrial network IntIon

Henrik Ehlers, Karl-Josef Becker, Rudolf Beckmann, Nils Beermann, Ulf Brauneck, Peter Fuhrberg, Dieter Gaebler, Stefan Jakobs, Norbert Kaiser, Michael Kennedy, Friedrich Koenig, Sven Laux, Juergen Christian Mueller, Bernd Rau, Werner Riggers, Detlev Ristau, Dieter Schaefer, Olaf Stenzel

Proceedings Volume 5250, (2004) https://doi.org/10.1117/12.514817

KEYWORDS: Ions, Plasma, Niobium, Refractive index, Deposition processes, Resolution enhancement technologies, Coating, Prototyping, Oxygen, Absorption

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Proceedings Article | 7 September 1999 Paper

Broadband antireflection coatings deposited with ion-assisted evaporation

Sven Laux, Norbert Kaiser, Hansjoerg Niederwald, Michael Mertin, Henrik Ehlers, Detlev Ristau

Proceedings Volume 3738, (1999) https://doi.org/10.1117/12.360066

KEYWORDS: Magnesium fluoride, Coating, Antireflective coatings, Ions, Resistance, Reflectivity, Oxides, Plasma, Absorption, Refractive index

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Showing 5 of 29 publications

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