The Copernicus Land Surface Temperature Monitoring (LSTM) mission is part of the Copernicus Sentinel Expansion Missions.It will carry a high spatial-temporal resolution thermal infrared sensor to provide observations of the landsurface temperature.The mission responds to priority requirements of the agricultural user community for improving sustainable monitoring requirements to better manage water resources and learn about yield, vegetation and crop growth.The spectral coverage in the multiple bands spans from 490nm to 1610nm for the VNIR/SWIR part of the instrument.Materion Optics Balzers was selected as responsible supplier for the VNIR/SWIR filter assemblies.This contribution addresses the design, manufacturing and characterization of the demanding dielectric optical coatings for the sophisticated band pass filters and dichroic by PARMS technology for the LSTM project by Materion Optics Balzers.

We present highly miniaturized optical and electronic components for a two-channel fluorimeter with pin photodiodes with a very small detection limit (with an excitation of 100 mu W and 590 nm, we detect one nW at 650 nm). One potential application lies in continuous monitoring of blood glucose levels. In a first step, novel dichroic beam splitter cubes made of fused silica with an edge length of 3 mm were developed. The diagonally dividing surface of the cubes was provided with a new dichroic layer system using the PARMS (Plasma Assisted Reactive Magnetron Sputtering) coating technology, which made it possible to achieve an angle of incidence of 45 degrees (the current state of the art is more like 30 degrees). The wavelength ranges are between 560 and 800 nm. In a second step, a special LED lighting unit with dimensions of 4 mm by 6 mm by 5 mm was developed. The angular distribution in the excitation beam that hits a dichroic beam splitter cube is limited to 3 degrees. In addition, very thin optically direction-selective filters have been developed to reduce stray light on the photodiodes. Here, glass substrates with a 100 mu m thick Si-layer were used. This silicon layer was structured using inductively coupled plasma etching (ICP). Breakthroughs measuring 40 mu m by 40 mu m were created with inner walls made of black silicon. The transmission of these filters is 0.4 at angle of incidence at zero degrees and is less than 0.01 at angles of incidence greater than 13 degrees.

Multispectral earth observation is done using selected discrete filter channels. The optical filtering is typically accomplished using optical thin film filters. These filters can be placed in filter wheels or as an array directly in front of the detector. For compact system designs filter arrays are preferred. The manufacturing of filter arrays can be done by two different approaches called monolithic array and butcher block. Typical optical requirements for such filters are for example a filter transmission of above 90% and an out-of-band blocking in OD6 range.

Within the Copernicus program, the Sentinel-5/UVNS instrument is dedicated to the monitoring of air quality, trace gases and aerosols. The instrument consists of two co-aligned telescopes and five spectrometers in the spectral channels named UV1, UV2VIS, NIR, SWIR1, and SWIR3. The spectral band of UV1 spectrometer is defined from 270 nm to 310 nm. To distribute incoming light and eliminate false light into the channels and within the UV1 channel dedicated coatings for UV spectral range are needed. OBJ was selected for development and application of these coatings.

The Multi-viewing, Multi-channel, Multi-polarisation Imager (3MI) is one of the instruments of the “Satellite A” payload of MetOp-SG, developed to provide information on atmospheric aerosols. 3MI is a space based, wide-field-ofview spectroradiometer that is designed to acquire sequential images of the same ground target which are combined with multiple spectral views in both un-polarized and polarized channels. The spectral coverage in the multiple bands from 410 nm to 910 nm and from 910 nm to 2130 nm shall be done using a Filter Wheel Assembly which included the Filter Wheel Disk (FWD). OBJ was selected for development and production of these optical elements. This contribution addresses the manufacturing and characterization of the demanding dielectric optical coatings for the sophisticated BPFs developed by Optics Balzers.

Coated optical components with low surface form deviations require particular knowledge on thin-film stress. Contributing factors to stress in PARMS coatings are evaluated and results of laser mirrors, deposited on thin substrates, are presented.

Beside homogeneous filter coatings a coating can also be applied with a linear gradient. Linear gradient or linear variable filters show a gradient of a band edge or central wavelength depending on the filter type in spectral direction and they are homogeneous in spatial direction. In this paper, we present a linear variable narrow band pass filter with full width half maximum of about 8 nm and a transmittance of more than 98% in the wavelength range of 670 nm to 780 nm. The target for the gradient is 3.3. nm/mm. Due to the need of transmittance filter and AR coating are manufactured by means of Plasma Enhanced Magnetron Sputtering (PARMS). Additionally, the linear variable filter for FLEX mission requires a black mask to separate between HR1 and HR2 channel. This mask is also applied by OBJ by means of the PARMS process and a Ti based layer stack. Here, a reflectance of < 1.5% in the range of 400 nm to 800 nm can be demonstrated. The definition of black mask was done by means of photolithography.

Beam splitters separating visible (VIS) and near-infrared (NIR) light are an important component of many optical systems such as spectrometers or telescopes. Here, one part of the spectrum is transmitted while the other is reflected. Typical goal requirements are broadband high transmittance and high reflectance without local minima combined with a steep transition zone. These requirements drive the complexity of the coating design. Beside the coating design also the deposition technology has an impact on the feasibility of the coating. In this contribution, we address manufacturing challenges for manufacturing of an ideal beam splitter and compare Ion Assisted Deposition (IAD) and Plasma Enhanced Magnetron Sputtering (PARMS) technology by presenting examples of VIS-NIR beam splitters manufactured at Optics Balzers Jena GmbH (OBJ). These examples reach from beam splitters manufactured by IAD with a total coating thickness of about 3.5 μm to the beam splitter of Sentinel 2 multi-spectral instrument with more than 100 layers a and a coating thickness of about 13 μm. An example which overcomes the limitations of the IAD process is the dichroic plate of ESAs Euclid telescope manufactured by OBJ by means of PARMS process. This dichroic plate shows a reflectance of over 99% in the VIS spectral range and a transmittance of more than 98% in the NIR spectral range. Both mentioned manufacturing technologies are discussed in terms of process stability, coating homogeneity, and straylight limitations.

The extraordinary specification for the dichroic beamsplitter inside the Euclid telescope requires very complex coatings. Design issues considering the several boundary conditions are discussed and results from the current development are presented.

Scattering in thin-film filters is mainly driven by the substrate roughness and the deposition technology but also by the coating design as well as by the filter orientation. A high-energy, low-loss coating technology (plasma-assisted reactive magnetron sputtering, PARMS) was used to deposit an advanced thin-film filter design on substrates with low micro roughness. This approach resulted in a significantly reduced level of scattered light as well as an excellent spectral performance of the produced filters. Compared to coatings deposited by ion-assisted evaporation (IAD), the level of out-of-band scattering could be reduced by more than 2 orders of magnitude to about 0.001%.

The Sentinel 2 mission shall ensure the continuity and enhancement of Landsat and SPOT data and sustain operational land services in the frame of the Global Monitoring for Environment and Security (GMES) initiative. Sentinel-2 is designed to image the Earth’s landmasses from its orbit for at least 7.25 years. The Multi-Spectral Instrument (MSI), delivered by Astrium Toulouse, will provide high resolution imagery in 13 spectral channels extending from the Visible Near Infrared (VNIR, 400-1100 nm) to the Short Wave Infra-Red (SWIR, 1100-2500 nm) range, down to a resolution of 10 meters with an image width of 290 kilometers. A dichroic splitter device is located in back-focal path of the telescope. It allows splitting the incoming optical beam between VNIR and SWIR focal planes. It shall ensure an extremely high rejection, better than 1:1000, between both ranges while introducing negligible aberrations in reflected (VNIR) and transmitted (SWIR) paths. The splitter assembly consists of a wedged dichroic filter plate and a wedged compensator plate mounted in a common frame. Both plates are made of fused silica (Infrasil) and polished to lambda/40. The major challenges reside in the design complexity of the dichroic coating and in the deposition process control to ensure the required high uniformity of performances through the large aperture. The paper presents the final spectral and optical performances of this challenging sub-system. It also discusses the main difficulties that have been overpassed during the development and qualification phase.

Reduced optical density of dielectric broad blocking filters can be attributed to substrate surface properties. Applying the model of small-scale roughness by interface overlayers, the suitability of given substrate polishing quality can be assessed.

For more than four decades band-pass filters are important components of microscopes used for the fluorescence spectroscopy. During all the time this special field of application has been one of the main drivers for research and development in thin-film optics, particularly for the thin-film design software and the coating technology. With a shortwave pass filter, a multi-notch filter, and a classical band-pass filter as examples of such filters provided for the latest generation of fluorescence microscopes we present the state-of-the-art in coating design and technology. Manufacturing these filters is a great challenge because the required spectral characteristics need necessarily multilayers with up to 300 layers and overall thicknesses up to 30 μm. In addition, the designs require also 3 to 5 nm as thinnest layers and all the layers are completely of non-quarterwave type. The filters were manufactured in a rapid-prototyping regime by a Leybold Helios plant using plasma-assisted reactive magnetron sputtering of thin films of different metal oxides. Designed and real spectra are compared and differences are discussed. Measurement results of other optical and non-optical characteristics as film stress, total integrated scattering, and micro roughness are presented.

Besides the typical channels in the visible and near infrared spectrum, optical remote sensing of the earth from air and space utilizes also several channels in the short-wave infrared spectrum from 1000 nm to 3000 nm. Thin-film optical filters are applied to select these channels, but the application of classical multiple-cavity band-pass filters is impossible. Because of their additional blocking elements they are disallowed due to geometrical or other non-optical reasons. Within the sensitivity region of an MCT detector as typical detector device, the selection and blocking of radiation by the filter has to be provided by a single multilayer system. The spectral region of the SWIR as well as blocking width and depth require necessarily designs with overall thicknesses of more than 20 μm, with layer numbers up to 100. SiO 2 and TiO 2 were used as thin-film materials deposited with reactive e-beam evaporation under ion assistance in a Leybold SyrusPro box coater. A special challenge was the thickness measurement of the thin films by an optical broadband monitoring device in the visible range. The results of manufacturing and characterizing of such filters are presented by three examples for the center wavelengths of 1375 nm, 1610 nm, and 2190 nm.

Material mixtures offer new possibilities for synthesizing coating materials with tailored optical and mechanical properties. We present experimental results on mixtures of HfO2, ZrO2, and Al2O3, pursuing applications in UV coating technology, while the mixtures are prepared by magnetron sputtering, ion beam sputtering, plasma ion-assisted deposition (PIAD), and electron beam evaporation without assistance. The properties investigated include the refractive index, optical gap, thermal shift, and mechanical stress. The first high reflectors for UV applications have been deposited by PIAD.

Rugate designs for the realization of notch filters are well known in the literature. The required deposition of gradient index layers is difficult to manufacture. In our approach we apply the equivalent index theory to replace the gradient index profile of a notch filter design. We produce single and multiple notch filters with plasma ion-assisted deposition and broad-band optical monitoring. As examples, a 500nm notch filter for the GREGOR telescope and a 589nm notch filter for the GALACSI instrument of the VLT are discussed. Additionally, a 4-line multiple notch filter and a 218nm notch filter made for fluorescence spectroscopy applications are presented.

For single layers of SiO2, Nb2O5, and Ta2O5 that are deposited by plasma-assisted reactive magnetron sputtering (PARMS), we present measurement results for basic optical and mechanical properties, in particular, optical index, intrinsic film stress, thermal shift of spectral transmittance, and microroughness. We find high refractive indices combined with low intrinsic film roughness, moderate compressive stress, and almost a vanishing shift, indicate high potential for the production of high-performance optical coatings. The high thickness accuracy and process stability are exemplified by the measured spectral performance of multilayer stacks with about 200 single layers.

Material mixtures offer new possibilities of synthesizing coating materials with tailored optical and mechanical properties. We present experimental results on mixtures of HfO2, ZrO2, and Al2O3 pursuing applications in UV coating technology.

A precise identification of the dielectric materials dispersion data, involved forming the layer stack, is crucial for obtaining satisfactory results utilizing optical broadband monitoring for high precision control of thin-film optical filters.