Christoph Gerhard

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

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...

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...

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...

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...

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 [...]

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...

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...

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...

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...

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 [...]

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...

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...

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....

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...

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...

It is told that Theodore Maiman called the first operating laser source he and his co-worker Charles Asawa realized 60 years ago [...]

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.

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...