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Importance Extenuating circumstances can trigger unplanned changes to randomized trials and introduce methodological, ethical, feasibility, and analytical challenges that can potentially compromise the validity of findings. Numerous randomized trials have required changes in response to the COVID-19 pandemic, but guidance for reporting such modifications is incomplete. Objective As a joint extension for the CONSORT and SPIRIT reporting guidelines, CONSERVE (CONSORT and SPIRIT Extension for RCTs Revised in Extenuating Circumstances) aims to improve reporting of trial protocols and completed trials that undergo important modifications in response to extenuating circumstances. Evidence A panel of 37 international trial investigators, patient representatives, methodologists and statisticians, ethicists, funders, regulators, and journal editors convened to develop the guideline. The panel developed CONSERVE following an accelerated, iterative process between June 2020 and February 2021 involving (1) a rapid literature review of multiple databases (OVID Medline, OVID EMBASE, and EBSCO CINAHL) and gray literature sources from 2003 to March 2021; (2) consensus-based panelist meetings using a modified Delphi process and surveys; and (3) a global survey of trial stakeholders. Findings The rapid review yielded 41 673 citations, of which 38 titles were relevant, including emerging guidance from regulatory and funding agencies for managing the effects of the COVID-19 pandemic on trials. However, no generalizable guidance for all circumstances in which trials and trial protocols might face unanticipated modifications were identified. The CONSERVE panel used these findings to develop a consensus reporting guidelines following 4 rounds of meetings and surveys. Responses were received from 198 professionals from 34 countries, of whom 90% (n = 178) indicated that they understood the concept definitions and 85.4% (n = 169) indicated that they understood and could use the implementation tool. Feedback from survey respondents was used to finalize the guideline and confirm that the guideline’s core concepts were applicable and had utility for the trial community. CONSERVE incorporates an implementation tool and checklists tailored to trial reports and trial protocols for which extenuating circumstances have resulted in important modifications to the intended study procedures. The checklists include 4 sections capturing extenuating circumstances, important modifications, responsible parties, and interim data analyses. Conclusions and Relevance CONSERVE offers an extension to CONSORT and SPIRIT that could improve the transparency, quality, and completeness of reporting important modifications to trials in extenuating circumstances such as COVID-19.

Software is as integral as a research paper, monograph, or dataset in terms of facilitating the full understanding and dissemination of research. This article provides broadly applicable guidance on software citation for the communities and institutions publishing academic journals and conference proceedings. We expect those communities and institutions to produce versions of this document with software examples and citation styles that are appropriate for their intended audience. This article (and those community-specific versions) are aimed at authors citing software, including software developed by the authors or by others. We also include brief instructions on how software can be made citable, directing readers to more comprehensive guidance published elsewhere. The guidance presented in this article helps to support proper attribution and credit, reproducibility, collaboration and reuse, and encourages building on the work of others to further research.

Software is as integral as a research paper, monograph, or dataset in terms of facilitating the full understanding and dissemination of research. This article provides broadly applicable guidance on software citation for the communities and institutions publishing academic journals and conference proceedings. We expect those communities and institutions to produce versions of this document with software examples and citation styles that are appropriate for their intended audience. This article (and those community-specific versions) are aimed at authors citing software, including software developed by the authors or by others. We also include brief instructions on how software can be made citable, directing readers to more comprehensive guidance published elsewhere. The guidance presented in this article helps to support proper attribution and credit, reproducibility, collaboration and reuse, and encourages building on the work of others to further research.

The Enabling FAIR Data project has brought together a broad spectrum of Earth, space, and environmental science leaders to ensure that data are findable, accessible, interoperable, and reusable.

Supermemories are coming that will store an entire library or home-cinema collection on a single chip

Diffractive phase elements (DPE), consisting of a patterned UV-transparent layer on a UV-transparent substrate, were fabricated by three steps. A UV-absorbing SiO x -coating (x < 2) with a thickness matching to the required phase delay was deposited on a fused silica substrate. The coating was removed on a pixel array corresponding to a calculated two-dimensional quantized phase function (DPE-design). By a thermal annealing process the SiO x -coating was oxidised to UV-transparent SiO 2 , resulting in a UV-grade surface relief element.

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF/sub 3/, AlF/sub 3/, and MgF/sub 2/. Spectral- and time-resolved measurements reveal the presence of cerium in LaF/sub 3/ and the influence of hydrocarbons in MgF/sub 2/ and LaF/sub 3/. Virtually no fluorescence response is observable in the case of AlF/sub 3/. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF/sub 3/. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra.

A review of the recent progress in intersubband transitions in GaN-based superlattice structures grown by plasma-assisted molecular beam epitaxy (MBE) is presented. Careful control of the growth parameters resulted in reduced threading dislocation density as well as optimized interfaces for the superlattices. Intersubband absorption has been observed from a variety of configurations involving GaN single or asymmetric double quantum wells with either thick Al x Ga 1-x N barriers or short-period GaN/Al x Ga 1-x N superlattice barriers. The peak wavelength of absorption can be varied between 1.4-4.2 μm by changing the quantum well thickness. Electron scattering times were measured by the pump-probe technique and were found to be 240-330 fs at 1.55 μm. In addition, intersubband transitions have also been observed for GaN/AlN superlattices grown with a non-polar (1120) orientation.

Time-resolved luminescence experiments have been set up in order to study the interaction of 193-nm laser radiation with dielectric thin films. At room temperature, Al/sub 2/O/sub 3/ coatings show photoluminescence upon ArF excimer laser irradiation, with significant intensity contributions besides the known substrate emission. Time- and energy-resolved measurements indicate the presence of oxygen-defect centers in Al/sub 2/O/sub 3/ coatings, which suggests a strong single- photon interaction at 193 nm by F/sup +/ and F center absorption. Measurements on highly reflective thin-film stacks, consisting of quarter-wave Al/sub 2/O/sub 3/ and SiO/sub 2/ layers, indicate similar UV excitations, mainly from color centers of Al/sub 2/O/sub 3/

Growing requirements for the optical and environmental stability, as well as the radiation resistance against high-power laser radiation, especially for optical interference coatings used in the ultraviolet spectral range, have to be met by new, optimised, thin-film deposition technologies. For applications in the UV spectral range, the number of useful oxide thin film materials is very limited due to the higher absorption at wavelengths near to the electronic bandgap of the materials. Applying ion-assisted processes offers the ability to grow dense and stable films, but in each case careful optimisation of the deposition process (evaporation rate, substrate temperature, bombarding gas, ion energy and ion current density) has to achieve a balance between densification of the layers and the absorption. High-quality coatings and multilayer interference systems with SiO/sub 2/ as the low- index material can be deposited by various physical vapour deposition technologies, including reactive e-beam evaporation, ion-assisted deposition and plasma ion-assisted deposition. In order to improve the degradation stability of dielectric mirrors for use in UV free-electron laser optical cavities, a comparative study of the properties of SiO/sub 2/, Al/sub 2/O/sub 3/ and HfO/sub 2/ single layers was performed, and was addressed to grow very dense films with minimum absorption in the spectral range from 200 to 300 nm. The films were deposited by low-loss reactive electron-beam evaporation, by ion-assisted deposition using a 'Mark II' ion source, and by plasma ion-assisted deposition using the advanced plasma source. Optical and structural properties of the samples were studied by spectral photometry, infrared spectroscopy, X-ray diffraction and reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energy values close to the bandgap was studied. For HfO/sub 2/ single layers, laser-induced damage thresholds at 248 nm were determined in the 1-on-1 and 1000-on-1 test modes as a function of the deposition technology and film thickness.

The demand to enhance the optical resolution, to structure and observe ever smaller details, has pushed the search for technological innovations and improvements. Induced mainly by the production of more powerful electronic circuits with the aid of projection lithography, optics developments in recent years can be characterized by the use of electromagnetic radiation with smaller wavelength. This paper covers some theoretical considerations, material aspects, design and different techniques of controlled fabrication of multilayer coated optics. Their potential applications for microlithography as well as alternative application fields like microscopy, spectroscopy, soft X-ray lasers and free electron lasers are also discussed.

Small oscillations of surface electrons that manipulate light on the nanoscale could be the route to applications as disparate as faster computer chips and cures for cancer. Joerg Heber reports.

Thin films of oxygen-bearing compounds could have myriad practical applications, finds Joerg Heber, if a few problems can be overcome.

Microelectronics made from silicon will soon be as small as they can physically be. The era of nanoelectronics dawns – where carbon could be king

Although the Internet has fundamentally changed the way we communicate, science publishing is remarkably hesitant in making full use of the potential offered by new technology.

We report on electron transport in growth direction and relaxation mechanisms in δ-doped GaAs-superlattices. In order to investigate pure electron transport, n-type δ–n–i–p–i structures sandwiched between two n+-cladding layers have been investigated, with doping induced barrier heights ΔV smaller than the band gap energy Eg of the host material. An exponential increase of the current is expected with increasing bias due to tunneling through a decreasing barrier. At elevated temperatures, thermally activation over the barriers becomes possible. A simple WKB-model describes the experimental data reasonably well. Moreover, a current step appears in the I–V characteristics at a critical field which is clearly below the breakthrough value. Opto-electrical measurements confirm the existence of holes in the structure at fields larger than the critical field. A model is presented which explains the photocurrent and electroluminescence measurements consistently. The key mechanism is based on a few ballistically traveling electrons that can gain enough energy for interband avalanche multiplication.

We report on a comparative study of room temperature intersubband electron scattering lifetimes in GaN/AlGaN single and coupled double multiple quantum well (QW) samples with peak absorption wavelengths ranging from 1.4 to 1.7 μm. Using time-resolved pump-probe spectroscopy electron scattering times as short as ∼160 fs have been measured for a coupled QW sample and ≲300 fs for single QW samples. While no significant dependence on the excitation power has been observed, a decrease of the scattering times with increasing probe wavelength has been measured and may be attributed to monolayer fluctuations in the samples.

Negative luminescence operation is reported for p–n diode devices with type-II InAs/InAsSb strained-layer-superlattice active regions which have a spectral peak at 4.2 μm and a negative luminescence efficiency of up to 20%.

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

300 K light-emitting diodes which emit at 5 and 8 μm with quasi-cw output powers of up to 50 and 24 μW, respectively, are reported. The devices have a single molecular beam epitaxy grown InAs/In(As, Sb) quantum well in the active region with a strong type-IIa band alignment giving mid-IR emission at energies up to 64% lower than the alloy band gap. The emission energies are shown to be in good agreement with a k⋅p bandstructure model where Qc, the ratio of the strained conduction-band offset to the band-gap difference between the two strained superlattice components, is found to be ∼2.0.

We report lasing of optically pumped Ga(AsNP)/GaP multiple quantum-well structures grown pseudomorphically on GaP substrate. A distinct threshold behaviour is observed at both cryogenic and room temperature; modal gain of up to 20 cm-1 is determined.

Realizing monolithic optoelectronic integrated circuits (OIECs) on silicon substrate would open up an exciting and completely new field of applications, i.e. optical interconnects at the chip level. In the past a lot of effort has been devoted to the growth of standard direct band gap III-V compound semiconductors on Si substrate, i.e. GaAs/Si or InP/Si. Due to the large lattice mismatch of these materials to the Si substrate large densities of threading dislocations are formed in the layers, preventing any long-term stable lasing operation of corresponding device structures. In this study the authors present a novel direct band gap material ( Ga(NAsP) ), which can be grown lattice-matched to GaP. Due to the similar lattice constant of GaP and Si, this novel material system might lead to the real monolithic integration of III/V-based optoelectronics and Si-based microelectronics in the near future

Since excimer laser applications extend to deep and vacuum UV wavelengths at 248 nm, 193 nm and 157 nm, renewed research interest has recently arisen on fluoride thin films due to their unrivaled position as wide-band-gap material for the vacuum UV (VUV). Among these materials, only a very limited number can act as the high refractive index component in multiplayer interference stacks. Besides LaF 3 , gadolinium tri-fluoride is a potential candidate especially for wavelengths at about and below 200nm. We report on the evaluation of the structural properties, the optical properties with emphasis to the DUV - spectral range, and the mechanical properties of GdF 3 single layer by means of XRD, GIXR, AFM measurements, spectral photometry and by ex - situ mechanical stress analysis using the laser beam deflection method to measure the substrate deformation. The samples were deposited onto fused silica and silicon substrates by a low-loss evaporation technology in a BAK 640 coating plant applying various deposition conditions.

The present candidates for low loss dielectric optical coatings at VUV excimer laser wavelengths are fluorides. Within this group, only one material - namely lanthanum fluoride - is used almost exclusively as high index film material. In search of additional high index film materials for use in VUV we investigated a broader spectrum of lanthanide tri-fluorides since little is known about their properties and the advantages or disadvantages with regards of their use in DUV- and VUV - optical stacks. Fluorides of lanthanum, neodymium, samarium, gadolinium, ytterbium and also yttrium were evaporated thermally. Precision VUV-measurement were initiated to give an overview of the ranges of UV-transparency up to the absorption edges and to determine the optical indices of these coating materials. Supplementary, also stress measurements, atomic force microscopy and XRD measurements were performed to scrutinize the properties of the films.

A set of ${(\mathrm{Ga}}_{0.77}{\mathrm{In}}_{0.23})\mathrm{As}∕\mathrm{Ga}({\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x})$ heterostructures is studied by time-resolved photoluminescence. Four samples with nitrogen concentrations from $x=0.48%$ up to $x=2.2%$ are investigated at different temperatures and with different excitation densities. The experiments suggest that the heterostructure band offset is type I for $x=0.48%$ and type II for $x=2.2%$. The situation is more complex for $x=0.72%$ and $x=1.25%$, since these samples are close to the transition from type I to type II. The experimental findings are analyzed using a detailed microscopic theory. Numerical calculations describe the measured data well. In particular, the interpretation of the experimental results concerning the band alignment is confirmed by the theoretical analysis.

The paper proposes to review briefly steps of classical experimental progress towards resistant VUV-XUV coatings. It intends to address some of the new challenges of the VUV-XUV radiation resistant coatings, including material investigations, manufacturing, characterizations and active optical components.

We present a study of the optical properties of different GaN/AlGaN multiple quantum well heterostructure samples. In particular, a comparative study of room temperature intersubband electron scattering lifetimes in a variety of single and coupled quantum well samples is presented for different excitation powers and wavelengths. All samples were grown by molecular beam epitaxy on sapphire substrate. Typical quantum well widths of ~10 to 15 a were used together with AlN bulk and superlattice barriers with an AlN-mole fraction of ~0.65 and ~0.9, respectively. In absorption measurements, the single quantum well samples show intersubband absorption peaks ranging from ~1.4 to ~1.7 μm wavelength. Two absorption peaks at ~1.75 and ~2.45 μm were measured for an asymmetric coupled double quantum well structure. The intersubband electron scattering lifetimes were determined with time resolved pump-probe measurements using pump and probe beams with a pulse width of ~130 fs and wavelengths of ~1.55 and ~1.7 μm, respectively. For the single quantum well samples, intersubband scattering lifetimes of ~260 to ~300 fs have been measured. For the upper excited state of the coupled double quantum well, a lifetime of ~230 fs has been found.

Since excimer laser applications extend to deep and vacuum UV wavelengths at 193 nm and 157 nm, renewed research interest has recently arisen on fluoride thin films due to their unrivaled position as wide-band-gap material for the vacuum UV (VUV). In order to evaluate the development of mechanical stress in all dielectric fluoride mirrors which causes difficulties to grow the layer stacks on fused silica substrates with a sufficient large number of quarter-wave pairs of a low (L) and of a high index (H) fluoride material, a systematic study was performed on evaporated quarter-wave stacks of LaF3/MgF2 and LaF3/AlF3 with a growing number of LH-pairs. The samples deposited onto fused silica and silicon substrates by a low-loss evaporation technology in a BAK 640 coating plant were investigated by means of complex ex - situ mechanical stress analysis including temperature dependence of stress, optical measurements, infrared measurements, evaluation of structural and morphological parameters by AFM and XRD. When deposited at high substrate temperature of about 300°C, the LaF3/MgF2 tends show high tensile stress due to the thermal stress component arise from the large thermal expansion coefficient difference between the substrate and the film materials resulting in micro crack formation already starting after deposition of about 10 layer pairs. LaF3/AlF3 appear to have a larger crack resistance due to lower stress which can be correlated to the higher water content in these kind of stacks. By adjusting the deposition temperature, mirror stacks with high reflectance at 193nm can be grown.

Mechanical stress, microstructure and thermal-elastic properties of thin evaporated MgF2 films were studied in dependence on substrate temperature. Data on biaxial modulus and coefficient of thermal expansion of 50nm thick films are presented.

We report on our investigations of spectrophotometric measurements in the vacuum UV. A commercially available VUV setup at Fraunhofer IOF is used to illustrate spectrally and angle-resolved reflection and transmission measurements together with an in-situ sample irradiation by a F2-excimer laser.

Radiation resistance of optical materials against synchrotron radiation is important, if optical components for the high energetic regime have to be produced. In the framework of the European project EUFELE, which deals with the development of optical coatings for the free electron laser at ELETTRA (Trieste), a set of CaF 2 substrates was irradiated with synchrotron radiation. The synchrotron radiation was varied by wavelength, dose, and high energetic background illumination. Before and after irradiation, the CaF 2 substrates were investigated spectrophotometrically in the VUV, VIS and IR range. The surface topology was characterized by Nomarski microscope methods. Structure investigations were carried out with X-ray diffraction measurements. CaF 2 shows different types of degradation like color center formation, surface modification, and increased VUV absorption bands. Defect formation will be presented in dependence of synchrotron irradiation conditions.

Luminescence measurements have been set up in order to study the interaction of UV-laser radiation with dielectric thin films. The pulsed laser excitation was carried out at 193-nm (6.4eV), the coating materials comprised wide-band-gap oxides and fluorides. Experiments show the significant optical response of single- and multilayer coatings on the low fluence excitation at sub-band-gap energy. Time- and spectrally-resolved measurements indicate characteristic emission bands of color centers in the deep-UV and vacuum-UV coating materials. An assignment of these optical transitions can be derived from the comparison with known bulk-material studies.

A major challenge to increasing bandwidth in optical telecommunications is to encode electronic signals onto a lightwave carrier by modulating the light up to very fast rates. Polymer electro-optic materials have the necessary properties to function in photonic devices beyond the 40-GHz bandwidth currently available. An appropriate choice of polymers is shown to effectively eliminate the factors contributing to an optical modulator's decay in the high-frequency response. The resulting device modulates light with a bandwidth of 150 to 200 GHz and produces detectable modulation signal at 1.6 THz. These rates are faster than anticipated bandwidth requirements for the foreseeable future.

Working with wavelengths shorter than the deep ultraviolet involves the development of dedicated optics for free-electron lasers with devoted coating techniques and characterizations. High-performance deep- ultraviolet optics are specially developed to create low-loss, high- reflectivity dielectric mirrors with long lifetimes in harsh synchrotron radiation environments. In February 2001, lasing at 189.7 nm, the shortest wavelength obtained so far with free-electron-laser oscillators, was obtained at the European Free-electron-laser project at ELETTRA Synchrotron Light Laboratory, Trieste, Italy. In July 2001, 330- mW extracted power at 250 nm was measured with optimized transmission mirrors. Research and development of coatings correlated to lasing performance are reported.

Going to shorter wavelengths beyond the deep ultraviolet involves the development of dedicated optics for FEL with devoted coating techniques and characterizations. Low loss, high reflectivity dielectric mirrors with a long lifetime in a strongly harsh synchrotron radiation environment are required. In February 2001, lasing at 189.7 nm was obtained with Al/sub 2/O/sub 3//SiO/sub 2/ Ion Beam Sputtering mirrors, the shortest wavelength obtained so far with FEL oscillators. In July 2001, 330 mW extracted power was measured with optimized transmission mirrors. Coating research and development correlated to lasing performance obtained so far is reported.

The 2014 Nobel Prize in Physics has been awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura "for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources."

The optical performance and radiation stability of HR193nm - SiO2/Al2O3 – coatings deposited by different technologies (RE, PIAD, IBS) were systematically evaluated and causes for the low LIDT at 193nm compared to 248nm were investigated.

Recent interest in intersubband (IS) transitions in semiconductor heterostructures with large band offset has been fueled by attempts to extend the wavelength range of IS-based optical devices to the fiber-optics wavelength range around ~ 1.55 μm. GaN/AlGaN-based heterostructures are of particular interest due to their large effective electron mass and large longitudinal optical phonon energy. Both are essential to achieve ultrafast electron relaxation at large transition energies. IS absorption in GaN/AlGaN single and coupled double quantum wells (DQWs) has been measured. The samples were grown by molecular beam epitaxy on sapphire substrate and with a large (0.65 or 0.9) AlN-mole fraction in the barriers. Peak absorption wavelengths as short as 1.35 μm and 1.52 μm were measured for a symmetric DQW of 12 Å wide wells coupled by a 10 Å wide barrier, which also showed evidence of excited-state anti-crossing. As expected, asymmetric DQWs displayed no such anti-crossing, and the ground-state anti-crossing energies were found to be much smaller – as a result of the comparatively large effective electron mass – than the energy broadening of individual transitions. The asymmetric DQWs displayed peak absorption wavelengths between 1.5 and 2.9 μm. The electron relaxation time, attributed to longitudinal optical phonon scattering has been measured by pump-probe technique as 240 fs for a coupled DQW sample.

Despite the good education of its scientists, science and technology in Mexico faces multiple challenges, says Juan Ramon de la Fuente, a former Minister of Health and former Rector of the National Autonomous University of Mexico.

Slimline, efficient photovoltaics about to flop off the production line could revolutionise the business of generating electricity from sunlight

In order to improve the degradation stability of dielectric mirrors for the use in UV-Free Electron Laser optical cavities a comparative study of the properties of SiO2, Al2O3, and HfO2 single layers was performed which was addressed to grow very dense films with minimum absorption in the spectral range from 200 nm to 300 nm. The films have been deposited by low loss reactive electron beam evaporation, by ion assisted deposition using a Mark II ion source, and by plasma ion assisted deposition using the APS source. Optical and structural properties of the samples have been studied by spectral photometry, infrared spectroscopy, x-ray diffraction and - reflectometry, as well as by investigation of the surface morphology. The interaction of UV radiation with photon energies close to the band gap was studied. For HfO2 single layer, LIDT at 248 nm were determined in the 1-on-1 and the 1000-to-1 test mode in dependence on the deposition technology and the film thickness.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

InAs/InAsSb SQW LED's incorporating AlAs0.02Sb0.98 or In0.83Al0.17As electron confining barrier layers are reported. Devices emitting 108 (mu) W and 84 (mu) W at 300 K with QW emission at (lambda) equals 4.1 micrometer and (lambda) equals 4.7 micrometer exhibit quantum efficiencies that are improved by factors of 7 and 3.4 respectively over control samples without the barrier. The operating wavelength of negative luminescent (NL) devices with InAs/In(As,Sb) strained-layer-superlattice (SLS) active regions has been extended to (lambda) equals 6.8 micrometer. NL performance is limited by leakage currents that originate in the n+ contact layer.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New absorption measurements for aluminum oxide optical coatings at 193nm are presented. Apart from the strong linear absorption at this wavelength the data indicate a nonlinear absorption within the thin dielectric layer. By varying the laser thickness, the intrinsic contribution of the layer material to the overall absorption was separated from the contribution of the substrate and the interface. In addition, the conditioning behavior of the coatings was examined. A strong long term conditioning in the linear absorption was found for Al2O3 containing systems. Comparing the absorption and conditioning behavior of the single layers and a high-reflective system, we can show that the absorption properties of the HR-system are determined by its Al2O3 layers.

Optimization of deposition technologies improves the laser resistivity of fluoride multilayer coatings at wavelengths as short as 193 nm.

A mode-mismatched surface thermal lens technique with pulsed top-hat beam excitation and near field detection scheme is developed to measure in situ the thermoelastic response of UV dielectric coatings and bulk materials under excimer laser irradiation. The thermal lens technique is demonstrated to be not only convenient for an accurate determination of the laser-induced damage threshold (LIDT), but also sensitive to measure the thermoelastic response of dielectric coatings irradiated with fluences much below the LIDT, and hence, to carry out time resolved predamage investigation. The minimum detectable surface displacement of approximately 0.002nm is achieved with a simple experimental configuration. Nonlinear absorption of UV dielectric materials and coatings are demonstrated. The surface thermal lens technique is also a convenient technique to distinguish different damage mechanisms: thermal stress induced damage or melting induced damage, depending on the thermo-elastic properties of the substrate. Hence, this technique allows to indicate qualitatively the relative contribution of linear and nonlinear absorption as possible causes for laser damage. Moreover, the nonlinear effect in laser conditioning of a LaF3/MgF2 highly reflective dielectric coating has been observed experimentally.