Christoph Gerhard

Christoph Gerhard
Hochschule für angewandte Wissenschaft und Kunst - Hildesheim/Holzminden/Göttingen | HAWK HHG · Fakultät Ingenieurwissenschaften und Gesundheit

Prof. Dr. rer. nat.

About

160
Publications
15,794
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524
Citations
Introduction
Hi, my research currently focusses on the investigation of manufacturing-induced effects and defects on glass surfaces using LIBS, XPS etc. Moreover, plasma-induced phenomena are investigated...mainly on glasses, but also on other surfaces. I am always interested in new cooperations in these fields.
Additional affiliations
September 2021 - present
Politecnico di Milano
Position
  • Adjunct Professor
Description
  • Teaching in the field of Engineering Physics
September 2021 - present
Politecnico di Milano
Position
  • Adjunct Professor
Description
  • Teaching in the field of Engineering Physics
September 2021 - present
Politecnico di Milano
Position
  • Adjunct Professor
Description
  • Teaching in the field of Engineering Physics
Education
September 2010 - August 2014
Technische Universität Clausthal
Field of study
  • Physical Technologies
September 2008 - March 2010
September 2002 - August 2006

Publications

Publications (160)
Article
A passive cooling strategy without any electricity input has shown a significant impact on overall energy consumption globally. However, designing tunable daytime radiative cooler to meet requirement of different weather conditions is still a big challenge, especially in hot, humid regions. Here, a novel type of tunable, thermally insulating and co...
Article
Full-text available
Physical methods to control pest arthropods are increasing in importance, but detailed knowledge of the effects of some of these methods on the target organisms is lacking. The aim of this study was to use light sheet fluorescence microscopy (LSFM) in anatomical studies of blood-sucking arthropods in vivo to assess the suitability of this method to...
Article
Full-text available
Electrospun scaffolds can imitate the hierarchical structures present in the extracellular matrix, representing one of the main concerns of modern tissue engineering. They are characterized in order to evaluate their capability to support cells or to provide guidelines for reproducibility. The issues with widely used methods for morphological chara...
Article
Full-text available
Electrospun scaffolds have a 3D fibrous structure that attempts to imitate the extracellular matrix in order to be able to host cells. It has been reported in the literature that controlling fiber surface topography produces varying results regarding cell–scaffold interactions. This review analyzes the relevant literature concerning in vitro studie...
Article
Full-text available
Even though plasma is the most common state of aggregation in the known universe, its complex chemistry and physics, as well as its specifics and particular characteristics, are not yet fully understood [...]
Poster
This optimized material (resPUR-OT) has an excellent transparency, high thermal stability up to 344°C and provides the possibility of a simple and cost-effective dispensing technique to ensure a stable encapsulation of LEDs with the possibility of lens formation [2, 3]. The optical properties and the parameters of the band structure of PU can be ch...
Article
Impurities on glass surfaces, such as metallic trace contaminations induced by manufacturing processes, can cause severely disturbing effects as for example, a reduction in laser resistance or optical performance. Both the amount and nature of such impurities was thus investigated in the present work. For this purpose, fused silica surfaces were pr...
Article
Full-text available
Direct metal deposition (DMD) can be used for the cladding of surfaces as well as repairing and additive manufacturing of parts and features. Process monitoring and control methods ensure a consistent quality during manufacturing. Monitoring by optical emission spectroscopy of the process radiation can provide information on process conditions and...
Article
Full-text available
This paper reports on plasma-enhanced bonding of optics surfaces coated with highly sensitive functional layers using surface preparation by a dielectric barrier discharge (DBD) plasma. The samples to be bonded were treated with a DBD in diffuse mode at atmospheric pressure for 30 s which is applied directly to the sample surface, then joined with...
Article
Full-text available
In 1850, Austen Henry Layard discovered an approximately 3000-year-old, simple optical lens in Nimrud, Northern Iraq—the Nimrud lens, aka the Layard lens [...]
Article
In this contribution, we report on the influence of nitrogen-hydrogen plasma treatment on the chemical composition of fused silica surfaces with and without additional argon fluoride laser irradiation. Therefore, the compositions of pristine and plasma treated fused silica samples were investigated by secondary ion mass spectrometry before and afte...
Article
In this publication we report on the suitability of imaging ellipsometry for the semi-quantitative investigation of a contactless removal of human fingerprints from surfaces by an atmospheric pressure plasma treatment. Special attention is paid to the impact of the applied plasma on the complex mixture of biological substances of a fingerprint. For...
Article
Full-text available
The chemical composition of ground and polished fused silica glass surfaces plays a decisive role in different applications of optics. In particular, a high level of carbon impurities is often undesirable for further processing and especially for gluing or cementing where adhesion failure may be attributed to carbonic surface-adherent contaminants....
Article
Full-text available
In the course of classical optics manufacturing glass components are in permanent direct contact with aqueous operating materials. Such contact leads to a certain absorption of water and hydrogenous compounds that may induce severe glass defects. In this contribution, absorption of hydrogen and other contaminants during grinding of glass was observ...
Article
Echelle spectrometers enable the observation of large spectral windows with high resolving power in single recordings. However, these devices are strongly sensitive to temperature variations and even small changes may tamper both the wavelength and the intensity calibration. Here we propose a method for rapid checking and rectifying the calibration...
Article
Full-text available
It is told that Theodore Maiman called the first operating laser source he and his co-worker Charles Asawa realized 60 years ago [...]
Book
This book gives a comprehensive overview on the principles of optical imaging. It focuses on problem-based learning via multiple exercises and case examples and adresses optics and photonics students.
Article
Full-text available
One-dimensional nanomaterials including cellulose nanocrystals (CNCs) and gold nanorods (GNRs) are widely used in optical materials due to their respective inherent features: birefringence with accompanying light retardation and surface plasmon resonance (SPR). Herein, we successfully combine these properties of both nanorods to generate synergisti...
Article
Full-text available
We report quantitative analysis of manufacturing-induced trace contaminants of optical glass surfaces by laser-induced breakdown spectroscopy (LIBS). Therefore, spectra recorded with an echelle spectrometer coupled to a gated detector were analysed using a calibration-free LIBS approach based on the calculation of the spectral radiance of a plasma...
Chapter
Dieses Kapitel behandelt die Grundlagen zu optischen Medien. Dabei wird besonders auf optische Gläser eingegangen. Neben den Bestandteilen und der Herstellung optischer Gläser wird deren Charakterisierung näher erläutert. Darüber hinaus werden optische Sondermaterialien wie Kristalle, Glaskeramiken, Gradientenindexmaterialien, Kunststoffe und optis...
Chapter
In diesem Kapitel werden die grundlegenden Eigenschaften des Lichts behandelt. Dies umfasst die Lichtentstehung durch spontane Emission sowie die essentiellen Charakteristika von Licht wie die Photonenenergie, die natürliche Linienbreite sowie Polarisation und Kohärenz. Darüber hinaus wird auf den Welle-Teilchen-Dualismus, die elektromagnetische We...
Chapter
In diesem Kapitel wird eine Übersicht über Laserquellen sowie die Entstehung und die Eigenschaften von Laserlicht gegeben. Hierbei wird zunächst näher auf das Laserprinzip, die Besetzungsinversion und die stimulierte Lichtemission eingegangen. Es folgt die Darstellung des Aufbaus, der Bestandteile sowie der möglichen Betriebsarten und Typen von Las...
Chapter
In diesem Kapitel werden die wichtigsten optischen Komponenten vorgestellt und näher erläutert. Dies umfasst neben Planplatten, Umlenkprismen, Umkehrprismen und Dispersionsprismen auch Spiegel und unterschiedlichste Linsen. Zudem werden der Aufbau und die Funktionsweise optischer Schichten wie Reflexionsschichten, Antireflexschichten und Filterschi...
Chapter
Dieses Kapitel behandelt die Grundlagen der optischen Abbildung und die Entstehung von Abbildungsfehlern. Dazu wird zunächst auf unterschiedliche Abbildungsmodelle und deren jeweilige Gültigkeit eingegangen. Des Weiteren erfolgt die Definition der Auflösungsgrenze abbildender optischer Systeme sowie der darin auftretenden konjugierten Größen. Neben...
Chapter
In diesem Kapitel werden essentielle Grundbegriffe der Optik vorgestellt und näher erläutert. Hierbei wird im Besonderen auf den Brechungsindex, die optische Weglänge und die Grundlagen der Brechung an optischen Grenzflächen eingegangen. Darüber hinaus werden der nichtlineare Brechungsindex und die Doppelbrechung behandelt. Des Weiteren erfolgt ein...
Chapter
Dieses Kapitel bietet eine Übersicht über die wichtigsten optischen Systeme und Geräte. Hierbei wird eingangs auf den Aufbau des Auges eingegangen. Nachfolgend werden die Funktionsweisen von Lupen, Objektiven und Okularen, Endoskopen, Teleskopen und Mikroskopen behandelt. Darüber hinaus werden der Aufbau und die Funktionsprinzipien gängiger Interfe...
Article
Full-text available
In this contribution, we present a plasma-based approach for modifying the focal length of plano-convex lenses realised by the deposition of droplets made of optical cement. For this purpose, PMMA and soda-lime glass substrates were treated with a direct dielectric barrier discharge plasma at low pressure. To obtain plasma-induced changes in surfac...
Article
Full-text available
In this work we present a novel optical polymer system based on polyurethane elastomer components, which combines excellent UV transparency with high thermal stability, good hardness, high surface tension and long pot life. The material looks very promising for encapsulation and microlensing applications for chip-on-board (CoB) light-emitting diode...
Conference Paper
Finishing of optical components is one of the main challenging tasks in optics manufacturing. This includes precision polishing, smoothing, and surface modification, e.g. for subsequent contact bonding. Recent developments have shown that the use of dielectric barrier discharge plasmas at atmospheric pressure allows for the conception and realizati...
Poster
The optimized material (resPUR-OT) has an excellent transparency, high thermal stability up to 344°C and provides the possibility of a simple and cost-effective dispensing technique to ensure a stable encapsulation of LEDs with the possibility of lens formation [7, 8]. • The optical properties and the parameters of the band structure of PU can be c...
Article
Full-text available
In this publication, it is shown how to synthesize silver nanoparticles from silver cations out of aqueous solutions by the use of an atmospheric pressure plasma source. The use of an atmospheric pressure plasma leads to a very fast reduction of silver ions in extensive solvent volumes. In order to investigate the nanoparticle synthesis process, ul...
Conference Paper
In this contribution, the modification of optical and electrical properties of glasses by plasma treatment is introduced. The presented method is based on pulsed dielectric barrier discharge plasmas which are operated with hydrogenous working gases where atomic and excited hydrogen species are generated within the plasma by electron impact-induced...
Article
Full-text available
In this paper, the indirect monitoring of plasma-induced defect formation within fused silica via plasma emission spectroscopy is presented. It is shown that low-pressure plasma treatment with hydrogen as process gas leads to a decrease in UV transmission of fused silica. This decrease can be directly attributed to oxygen vacancy-related defects an...
Book
Dieses Lehrbuch bietet einen kompakten und einfachen Einstieg in die Optik und unterstützt Studierende der Physik, Technik und anderer angewandter Fächer beim Lernen und Verstehen der Grundlagen und Anwendungen. Der Autor liefert einen anschaulichen Überblick über die essenziellen Teilgebiete der Optik und behandelt die grundlegenden Mechanismen un...
Article
Full-text available
Cemented optical components and groups are essential devices for the realisation of modern systems and apparatuses used in a broad range of different applications such as telecommunications, imaging and even surgery. However, various parameters may affect the stability of cemented connections. In this context, the impact of dielectric barrier disch...
Conference Paper
Full-text available
In diesem Beitrag berichten wir über den Einfluss einer direkten dielektrischen Atmosphärendruckplasmaentladung auf die Femtosekundenlaserbearbeitung einer Aluminiumlegierung. Es wird gezeigt, dass das unterstützende Plasma die für diese Art der Laserbearbeitung typischen Oberflächenstrukturen beeinflusst und zudem das abgetragene Volumen signifika...
Article
Full-text available
In the last decades, laser machining of fused silica has gained in importance where the main challenge is to overcome the high transmission of this medium in order to achieve surface absorption. One approach is plasma treatment using hydrogenous process gases. In doing so, a near-surface glass layer is chemically modified by a removal of oxygen and...
Article
Full-text available
In this contribution, the surface uniformity of classically-manufactured fused silica windows was investigated via laser-induced breakdown spectroscopy. It is shown that for all investigated samples a comparatively high aluminium content was found at the edge of the surface with respect to its centre. This contamination can be attributed to residue...
Article
Full-text available
In this contribution, a plasma-based approach for finishing optics surfaces is introduced. Experiments were performed on classically manufactured zinc crown glass and sapphire. It is shown that the use of direct dielectric barrier discharge plasma at atmospheric pressure allows the removal of surface-adherent carbonaceous contaminations that were i...
Patent
Die Erfindung betrifft eine Vorrichtung (1) zur Bearbeitung einer Oberfläche (21) eines Werkstückes (2) mit einer Plasmaerzeugungs-einrichtung (4) und einer Laserstrahlerzeugungs-einrichtung (3), welche dazu eingerichtet sind, zumindest eine Teilfläche (25) der Oberfläche (21) des Werkstückes (2) mit Laserstrahlung (35) und Plasma (45) zu beaufschl...
Article
Full-text available
The laser-induced damage threshold of optics is an issue of essential importance in high-power laser applications. However, the complex and partially interacting mechanisms as well as the underlying reasons for laser damage of glass surfaces are not yet fully understood. The aim of the present work is to contribute to a better understanding of such...
Article
en Optical components used in normal ambient conditions are usually contaminated by hydrocarbons from the ambient air in the course of time. This contamination gives rise to a decrease in the particular optical performance, i.e. the reflectance of mirrors or the transmittance of lenses and windows. In order to address this issue, the impact of agei...
Article
Full-text available
In this contribution, we report on the impact of direct dielectric barrier discharge argon plasma at atmospheric pressure on femtosecond laser engraving of aluminium. It is shown that the assisting plasma strongly affects the surface geometry and formation of spikes of both laser-engraved single lines and patterns of adjacent lines with an appropri...
Book
Optical components are essential key elements in modern engineering and everyday life. The education of skilled personnel and specialists in the fields of theoretical and practical optics manufacturing is of essential importance for next-generation technologies. Against this background, this book provides the basis for the education and advanced tr...
Article
Full-text available
Laboratory plasmas inherently exhibit temperature and density gradients leading to complex investigations. We show that plasmas generated by laser ablation can constitute a robust exception to this. Supported by emission features not observed with other sources, we achieve plasmas of various compositions which are both uniform and in local thermody...
Article
We report on investigations of the spatial variations of contamination, roughness, and index of refraction of classically manufactured polished fused silica surfaces. Therefore, laser-induced breakdown spectroscopy was used to probe surface and subsurface impurities via the detection of aluminum. Measurements at different positions on the surface o...
Poster
The surface uniformity of optical properties of classically-manufactured glass surfaces may have a considerable impact on the final functionality of an optical component. Against this background, the grade and distribution of surface contamination by working materials used during classical manufacturing such as lubricants, lapping suspensions and p...
Article
In this work, we investigated the generation of particles during pure laser and plasma-assisted laser ablation of titanium. Experiments were performed using a NIR picosecond laser at a wavelength of 1030 nm and a pulse duration of 8 ps. For plasma-assisted ablation, an atmospheric pressure dielectric barrier discharge plasma was applied where the p...
Article
In this research, topographic, optical and chemical properties of zinc oxide layers deposited by a cold plasma-spray process were measured. Here, zinc micro particles were fed to the afterglow of a plasma spark discharge whereas the substrates were placed in a quite cold zone of the effluent plasma jet. In this vein, almost closed layers were reali...
Article
In this Letter we present a novel approach for increasing the nanosecond laser-induced damage threshold (LIDT) of sapphire windows. It is shown that after direct dielectric barrier discharge plasma treatment at atmospheric pressure for 90 s the LIDT is increased by a factor of 1.5 with respect to untreated samples. Several possible underlying mecha...
Article
en In this contribution, basic technically usable interactions of atmospheric pressure plasmas (APP), laser irradiation and solids as well as a technique which combines such plasmas and laser irradiation are introduced. Two examples for plasma‐enhanced laser processing of coatings on glass surfaces are presented in more detail. First, APP‐assisted...
Poster
The influence of the spatial distributions of temperature and densities on the accuracy of LIBS measurements based on modeling is presented. In particular, we illustrate the benefit of LIBS analyses in argon. Compared to the plasma produced by laser ablation in ambient air, the plume generated in argon appears almost uniform. This simplifies the pl...
Chapter
Atmospheric pressure plasmas are powerful tools for the activation of various material surfaces and thus allow significant increase in adhesion of glues or lacquers. Such increase is mainly due to a plasma-induced formation of polar groups at the surface. However, the activation of complexly-shaped free-form surfaces, which is quite easily to be re...
Conference Paper
In this contribution, basic technically usable interactions of atmospheric pressure plasmas (APP), laser irradiation and solids as well as a technique which combines such plasmas and laser irradiation are introduced. Two examples for plasma-enhanced laser processing of coatings on glass surfaces are presented in more detail. First, APP-assisted ann...
Chapter
In the last few years, the combination of laser irradiation with atmospheric pressure plasmas, also referred to as laser–plasma hybrid technology, turned out to be a powerful technique for different materials processing tasks. This chapter gives an overview on this novel approach. Two methods, simultaneous and sequential laser-plasma processing, ar...
Chapter
Dieses Kapitel behandelt die Grundlagen zu optischen Medien. Dabei wird besonders auf optische Gläser eingegangen. Neben den Bestandteilen und der Herstellung optischer Gläser wird deren Charakterisierung näher erläutert. Darüber hinaus werden optische Sondermaterialien wie Kristalle, Glaskeramiken, Gradientenindexmaterialien, Kunststoffe und optis...
Chapter
Dieses Kapitel behandelt die Grundlagen der optischen Abbildung und die Entstehung von Abbildungsfehlern. Dazu wird zunächst auf unterschiedliche Abbildungsmodelle und deren jeweilige Gültigkeit eingegangen. Des Weiteren erfolgt die Definition der Auflösungsgrenze abbildender optischer Systeme sowie der darin auftretenden konjugierten Größen. Neben...
Chapter
In diesem Kapitel werden die wichtigsten optischen Komponenten vorgestellt und näher erläutert. Dies umfasst neben Planplatten, Umlenkprismen, Umkehrprismen und Dispersionsprismen auch Spiegel und unterschiedlichste Linsen. Zudem werden der Aufbau und die Funktionsweise optischer Schichten wie Reflexionsschichten, Antireflexschichten und Filterschi...
Chapter
In diesem Kapitel werden essentielle Grundbegriffe der Optik vorgestellt und näher erläutert. Hierbei wird im Besonderen auf den Brechungsindex, die optische Weglänge und die Grundlagen der Brechung an optischen Grenzflächen eingegangen. Darüber hinaus werden der nichtlineare Brechungsindex und die Doppelbrechung behandelt. Des Weiteren erfolgt ein...
Chapter
In diesem Kapitel werden die grundlegenden Eigenschaften des Lichts behandelt. Dies umfasst die Lichtentstehung durch spontane Emission sowie die essentiellen Charakteristika von Licht wie die Photonenenergie, die natürliche Linienbreite sowie Polarisation und Kohärenz. Darüber hinaus wird auf den Welle-Teilchen-Dualismus, die elektromagnetische We...
Chapter
In diesem Kapitel wird eine Übersicht über Laserquellen sowie die Entstehung und die Eigenschaften von Laserlicht gegeben. Hierbei wird zunächst näher auf das Laserprinzip, die Besetzungsinversion und die stimulierte Lichtemission eingegangen. Es folgt die Darstellung des Aufbaus, der Bestandteile sowie der möglichen Betriebsarten und Typen von Las...
Chapter
Dieses Kapitel bietet eine Übersicht über die wichtigsten optischen Systeme und Geräte. Hierbei wird eingangs auf den Aufbau des Auges eingegangen. Nachfolgend werden die Funktionsweisen von Lupen, Objektiven und Okularen, Endoskopen, Teleskopen und Mikroskopen behandelt. Darüber hinaus werden der Aufbau und die Funktionsprinzipien gängiger Interfe...
Article
Full-text available
We report on the characteristics of aluminium trihydrate filled poly(methyl methacrylate) composite (PMMA/ATH) coatings realised by plasma deposition at atmospheric pressure. For this purpose, PMMA/ATH powder was fed to a plasma jet where the process and carrier gas was compressed air. The deposited coatings were investigated by X-ray photoelectron...