Over the past few years the advent of atomic layer deposition (ALD) technology has opened new capabilities to the field of coatings deposition for use in optical elements. At the same time, there have been major advances in both optical designs and detector technologies that can provide orders of magnitude improvement in throughput in the far ultraviolet (FUV) and near ultraviolet (NUV) passbands. Recent review work has shown that a veritable revolution is about to happen in astronomical diagnostic work for targets ranging from protostellar and protoplanetary systems, to the intergalactic medium that feeds gas supplies for galactic star formation, and supernovae and hot gas from star forming regions that determine galaxy formation feedback. These diagnostics are rooted in access to a forest of emission and absorption lines in the ultraviolet (UV), and all that prevents this advance is the lack of throughput in such systems, even in space-based conditions. We outline an approach to use a range of materials to implement stable optical layers suitable for protective overcoats with high UV reflectivity and unprecedented uniformity, and use that capability to leverage innovative ultraviolet/optical filter construction to enable astronomical science. These materials will be deposited in a multilayer format over a metal base to produce a stable construct. Specifically, we will employ the use of PEALD (plasma-enhanced atomic layer deposition) methods for the deposition and construction of reflective layers that can be used to construct unprecedented filter designs for use in the ultraviolet.
Optical coatings are key elements of any optical system. They can reduce surface reflection loss, isolate spectral bands, re-direct the light path and split light beams by wavelength. For decades, astronomers have made use of these special characteristics embodied in Anti-Reflection (AR) coatings, Band Pass (BP) filters, mirrors and Dichroic Beamsplitters (DBS). In the last several years, a need has arisen for much larger high performance filters and coatings. This is being driven by the ever increasing size of new and planned telescopes with their correspondingly larger focal planes.
Typical Broadband filters require modest wavelength uniformity and can be produced in legacy (existing) coating chambers, even in fairly large formats. However, some new instruments require narrow BP (NBP) filters of 60 cm or greater diameter in order to perform efficiently. Some planned systems will even require filters in the 75 cm diameter range. The implications for coating such large, very expensive optics are that the equipment must not only accommodate a large optic, but the process must achieve excellent uniformity over broad areas. It must also exhibit excellent performance, reproducibility and reliability in depositions consisting of well over one hundred layers and many hours duration. And finally, the spectral performance must be verifiable, not through an indirect method, but directly of the science optic itself. To address these challenges, Materion designed, built, tested and put into production a purposebuilt laboratory. This paper will describe in detail the elements of the lab creation and initial achievements.
Multi-spectral Earth imaging sensors commonly use edge-bonded filter arrays (also known as “butcher blocks”) for
spectral selection. These arrays are built from small filter “sticks” that are diced from coated wafers and then bonded
together and placed in very close proximity to the detector array. Some filter designs are susceptible to excessive high
angle scatter if the filters are constructed under less than ideal deposition conditions. This scatter can lead to optical
crosstalk, which degrades system performance. Insufficient specifications and sub-optimum manufacturing practices
lead to a phenomenon called angle resolved scatter (ARS), where light that should have been rejected by the filter is
scattered into a very high-angle leak path, leading to optical crosstalk. The Landsat Data Continuity Mission’s
(LDCM’s) operational land imager (OLI) instrument uses proximal filter arrays for spectral selection, so it is important
to quantify the amount of transmitted, scattered light in wavelength ranges outside the pass band. This paper describes
the scatter measurement techniques and Bi-Directional Transmission Distribution Function (BTDF) results for 3 OLI
This paper presents a summary of the performance of the Landsat Operational Land Imager (OLI) spectral filters. An
overview of OLI is presented along with background on filter performance and manufacture. Performance results versus
requirements are presented for all key performance metrics.
Advanced optical bandpass filters for the Hubble Space Telescope (HST) advanced camera for surveys (ACS) have been developed on a filer-by-filter basis through detailed studies which take into account the instrument's science goals, available optical filter fabrication technology, and developments in ACS's charge-coupled-device detector technology. These filters include a subset of filters for the Sloan Digital Sky Survey which are optimized for astronomical photometry using today's charge-coupled- devices. In order for ACS to be truly advanced, these filters must push the state-of-the-at in performance in a number of key areas at the same time. Important requirements for these filters include outstanding transmitted wavefront, high transmittance, uniform transmittance across each filter, spectrally structure-free bandpasses, exceptionally high out of band rejection, a high degree of parfocality, and immunity to environmental degradation. These constitute a very stringent set of requirements indeed, especially for filters which are up to 90 mm in diameter. The highly successful paradigm in which final specifications for flight filters were derived through interaction amongst the ACS Science Team, the instrument designer, the lead optical engineer, and the filter designer and vendor is described. Examples of iterative design trade studies carried out in the context of science needs and budgetary and schedule constraints are presented. An overview of the final design specifications for the ACS bandpass and ramp filters is also presented.
Satellites, and consequently satellite instruments, are undergoing size, power, volume and cost reductions, due primarily to national budget and commercial economic considerations. As instruments have become smaller, so have the filters used by them. Presently, several systems employ miniature multicolor focal plane filters, and more are planned. This paper documents the status of the development and refinements of these specialized devices in order to inform the instrument designer as to some of the newly available filter options, and hopefully to encourage new ideas for their use.