Surface relief gratings manufactured by lithographic means being a candidate for VLT MOONS instrument's main dispersers

Surface relief gratings are well-established elements for high power laser applications, e.g. ultra-short pulse compression. A binary submicron period profile, realized by e-beam lithography and reactive ion beam etching in a dielectric material, is utilized for nearly one-hundred percent diffraction efficiency. Because these gratings are manufactured without any replication techniques, a high wave front accuracy and a low stray light background can be achieved. Spectroscopic applications require additional properties, i.e. a larger spectral bandwidth and Off-Littrow operation. We present new approaches for surface relief gratings realized either via multi-level staircase profiles or exploiting sub-wavelength features. The RVS spectrometer grating in ESA's GAIA mission is a prominent example where these techniques are already in use. The current contribution focuses on the results achieved during a pre-development performed for the MOONS instrument intended to operate at VLT

Books in Arabic Script

The chapter approaches the book in Arabic script as the indispensable means for the transmission of knowledge across Eurasia and Africa, within cultures and across cultural boundaries, since the seventh century ad. The state of research can be divided into manuscript and print studies, but there is not yet a history of the book in Arabic script that captures its plurilinear development for over fourteen hundred years. The chapter explores the conceptual and practical challenges that impede the integration of the book in Arabic script into book history at large and includes an extensive reference list that reflects its diversity. The final published version was slightly updated, and includes seven illustrations of six Qurans from the holdings of Columbia University Libraries, four manuscripts and two printed versions. Moreover, the illustrations are images of historical artifacts which are in the public domain - despite Wiley's copyright claim

Transmission Gratings relying on Huygens Metasurfaces for short-wave to long-wave infrared applications

In many spectroscopic applications, diffraction gratings are the pivotal optical component which is used to decompose white light into its spectrum. However, design and manufacturing of diffraction gratings for the infrared spectral domain operating in transmission bares its own challenges, i.e. a very limited choice of transparent materials. Here we present our effort on exploiting Huygens-metasurface structures for design and manufacturing of diffraction gratings intended for operation in the short-wave (around 2µm) up to the long-wave infrared region (>10µm). Silicon nano-pillars are the material system of choice since they exhibit the best compromise between optical performance and manufacturing feasibility. We present specific designs as well as measurement results of a demonstrator sample

Optical methods for measuring the feature size of optical diffraction gratings with nano-meter accuracy and implementation of suitable feedback control loops

Surface relief diffraction gratings offer a high flexibility in their design and thus allow to synchronize their optical performance with the specific requirements of the underlying application. However, the accuracy and the specific control of the manufacturing processes are of vital importance. In this contribution, we present optical methods relying on white-light ellipsometry and how they can be exploited for the measurement of the critical dimensions of manufactured surface relief grating structures. We will furthermore present suitable processes (relying on atomic layer deposition) and how they are used in a feedback loop to control the grating’s feature sizes on the nanometer scale

Optische Anordnung zur spektralen Zerlegung von Licht

An optical arrangement for spectral decomposition of light is disclosed. In an embodiment the optical arrangement includes a reflection diffraction grating, a first medium with a refractive index nin arranged on a light incidence side of the reflection diffraction grating; and a second medium with a refractive index nG arranged on a side of the reflection diffraction grating that faces away from the light incidence side, with nin>nG, wherein the optical arrangement is configured in such a way that light impinges on the reflection diffraction grating from the first medium at an angle of incidence &agr;, wherein a condition sin(&agr;)>nG/nin is satisfied, wherein the reflection diffraction grating comprises a layer system with at least one unstructured layer and at least one structured layer, wherein the at least one structured layer has a periodic structure with a period p in lateral direction, and wherein the period p meets the following conditions: p&lgr;/[nin*sin(&agr;)+nin]

Charge Relaxation within Silicon/Graphite Anodes – A Multi-Method Study

As silicon/graphite (SiG) composites are more commonly used as the anode active material in commercial Li-ion batteries, investigation of the (de-)lithiation behavior of the blended anodes becomes increasingly important. In this study, the charge redistribution between graphite and silicon was investigated in graphite-NMC 622 and SiG (23 wt.-% Si) – NMC 622 bilayer pouch cells using in situ and operando X-ray diffraction (XRD). In addition to XRD, ex situ and in situ optical microscopy (IOM), as well as microstructural resolved simulations using digital twins of the cells, were used. Different SOC values (0%, 25%, 50%, 75%, and 100%) and two different C-rates (0.1C and 0.5C) were compared in cells during operation and in the relaxed state. Insights into the relaxation process at 75% SOC were gained by tracking of the charge redistribution in IOM cells. Ex situ optical microscopy measurements reinforced the findings of the IOM measurements. Both XRD and optical microscopy showed the disappearance of charge in the graphite component of the SiG anode during the relaxation period (≥24h) at SOC ≤75%, indicating a redistribution of Li from graphite into Si in the anode. The simulations allowed tracking of the concentration of Li in both active material components, verifying the observations on the charge relaxation processes observed in the XRD and microscopy experiments. The gained insights can support a better understanding of aging of blended SiG anodes during operation

Wide band UV/Vis/NIR blazed-binary reflective gratings: two lithographic techniques investigation

We report on subwavelength reflective gratings for hyperspectral applications operating in the 340 nm-1040 nm spectral range. The blazed grating period is 30 μm and is composed of 2D subwavelength binary structures with sizes in-between 120 nm and 350 nm. We demonstrate the manufacturing of gratings on 3” wafers by two lithography technologies (e-beam or nanoimprint) followed by dry etching process. These subwavelength gratings enable broadband efficiency which is in average 15%-20% above the efficiency requirement for next generation of spectro-imagers for Earth observation missions and a wavefront error that is much smaller than the 100 nm requirement for space application

Simulation of Li Plating in Si/Graphite Composite Electrodes

Li-ion batteries play a key role especially for electric vehicles and portable electronics. However, additional improvements are needed, for example, to achieve the fast charging criteria given by the automotive industry. The performance characteristics of the batteries such as high energy or power density can be tuned by the electrode microstructure, composition, or choice of materials. One such promising material for the negative electrode is Silicon: Si exhibits a high theoretical capacity and is very abundant. On the other hand, Si shows a large volume expansion and low Li mobility. Thus, to take advantage of the high theoretical capacity and to limit the deformation during cycling, Si is mixed with Graphite to produce more practical Si/Graphite composite electrodes. In order to increase the cycle life of Si containing electrodes, it is critical to trace the degradation processes responsible for their performance loss. One major aging mechanism causing fast degradation and fundamental safety risks is Li plating. This deposition of a metallic Li phase on the surface of Si/Graphite anodes is barely studied in the literature yet crucial to improve the performance and safety of state-of-the-art Li-ion batteries. In our contribution we present simulation results of Si/Graphite composite electrodes including models for Li plating on Graphite and Si particles in 3D microstructure-resolved simulations. While focusing on the differing lithiation behaviors of Graphite and Si, the findings are validated with experimental results from our project partners. More specifically, we compare our simulations to multiple complementary techniques such as neutron depth profiling (NDP), post-mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling, and X-ray diffraction analysis (XRD). We examine commercial and self-manufactured full- and half-cells containing varying amounts of Si or SiC blend. Since inhomogeneities in the amount of Li plating were observed, studies on simplified half-cells are conducted to clarify the impact of relevant material parameters. Furthermore, we developed a homogenized p2D model of composite electrodes which also includes the volume changes during lithiation and delithiation of representative Si particles and the effect on transport processes. Not only provides the complementarity of sophisticated experimental and simulative studies a better understanding of how Li plating takes place in Si containing electrodes, but also enables an improved possibility to optimize the design of Si/Graphite composite electrodes

Wide band UV/Vis/NIR blazed-binary reflective gratings for spectro-imagers: two lithographic technologies investigation

We report on subwavelength reflective gratings for hyperspectral applications operating in a very large spectral band (340–1040 nm). Our study concerns a blazed-binary grating having a period of 30 μm and composed of 2D subwavelength structures with size from 120 nm to 350 nm. We demonstrate the manufacturing of the gratings on 3″ wafers by two lithography technologies (e-beam and nanoimprint) followed by classical dry etching process. Optical measurements show that the subwavelength grating approach enables a broadband efficiency, polarization behaviour and wavefront quality improvement with respect to the requirements for the next generation of spectro-imagers for Earth observation missions. An outlook towards spherical substrate based on nanoimprint lithography is also reported with the results of mixed features replication (holes and pillars in the range of 160–330 nm) on a 540 mm concave substrate which demonstrate uniformity and accuracy capabilities over 3″ surface