N251-057 TITLE: Dispersive Optics for Vacuum Ultraviolet Applications

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Space Technology

OBJECTIVE: Develop innovative methods to fabricate and replicate high quality dispersive optical components specifically geared for applications at ultraviolet (UV) and vacuum ultraviolet (VUV) wavelengths, for use within sensors in space on microsats and smallsats.

DESCRIPTION: The Navy is interested in the development of methods to fabricate and replicate cost-effective concave gratings and other dispersive optical elements needed to meet the demands of compact, proliferated optical systems designed for operation in space. Such elements are expected to be critical components of the next generation of small satellites to study the upper atmosphere, ionosphere, aurora, Sun, and solar-terrestrial space environment. Availability of customizable, high-quality optics of different optical figures, shapes, and dispersive properties will allow for future mission growth. The Navy is seeking to foster the development of affordable optical components and systems that could have broad application to space sensors and systems. Current UV and VUV grating technology involves substrates with machined or holographically ruled grooves, usually customized for single-use applications, with trade-offs on efficiency, scattered light, and often at high cost. For VUV applications, the product is typically coated to provide improved efficiencies, but with materials that are reactive to atomic and molecular oxygen, hydrocarbons, and other contaminants in the spaceflight environment. Advances in standard technology and innovative concepts and methods are sought to provide small-scale optics (target dimensions on the order of 5-10 cm) that have the potential to improve the cost, speed-of-manufacture and replication, customization, and applicability across the UV and VUV spectrum, while meeting or exceeding the optical performance, ruggedness, mass, and material properties necessary to meet the evolving demands of these new classes of space-based remote sensing instruments.

Dispersive elements applicable to both the UV and VUV (30-300 nm) are reflective due to the lack of refractive and transmissive materials at the shorter wavelengths. Total grating on-blaze efficiencies are typically on the order of 30% (near-normal incidence angle), but solutions including improvements in the combined blaze efficiency and coating reflectivity to achieve a higher overall efficiency will be taken into account. Low scattered light is a primary concern for space-environment applications where bright out-of-field and out-of-spectrum scattered light can obscure dimmer atmospheric emissions being observed. Spectral resolutions ranging from 0.1 to 2.0 nanometers, and/or groove spacing capabilities from 500-4000 l/mm, are desirable targets, with tolerances on the order of 20 l/mm. Precisely formed shapes ranging from flat to concave with radii of curvature as small as 10 cm are desired, including both spherical and toroidal surfaces. Additional consideration will be given to concepts that address grating-standard qualities including groove homogeneity, surface roughness, figure precision, or other corresponding performance factors.

Additional factors related to spaceflight compatibility are hardiness to contaminants, a coefficient of thermal expansion (CTE) compatible with typical spacecraft materials, low outgassing, survival at temperatures of -50° – +60°C, and the ability to survive a NASA GEVS3 vibration specification and thermal test environment, all typical of the requirements imposed for flight on small spacecraft. Technologies proposed should not contain hazardous or high outgassing materials and should be capable of being integrated into typical optical systems. It is desired that they be moderately electrically and thermally conductive to avoid developing static charge and thermal gradients in space. They should be durable and able to withstand normal optical component handling procedures. They should be delivered in an optically clean state and be robust enough to withstand precision cleaning and vacuum baking as part of normal spacecraft processing.

PHASE I: Demonstrate and document the feasibility of a dispersive optics concept and/or methodology for meeting Navy needs for compact satellite optical systems in the UV/VUV. Demonstrate the new methodologies for proof-of-concept and technical feasibility. Provide a demonstration by test or analysis that clearly identifies the possible gains of the concept made by advancing innovative methodologies, improving performance, and/or reducing cost and timeline for customized fabrication and replication from concept to delivery. Address performance capabilities, advantages, and limitations at all wavelengths in the spectrum from 30-300 nm as related to the optical performance metrics as presented in the Description in the Phase I report. Optical test reports and samples may also be provided for evaluation.

PHASE II: Develop a minimum of two prototype units of 10 mm size class, with different design parameters, for evaluation. The prototype designs should provide areas no less than 4 cm by 4 cm (objective) but not to exceed 10 mm in any dimension. Work with the Navy to define the complete set of details of the prototype based on the technology and methodology being developed. The prototype will be evaluated to determine its capability in meeting the performance goals defined in the Phase II Statement of Work (SoW) and the Navy need. Perform detailed environmental, shock, and vibration analysis to ensure materials are rugged and appropriate for Navy application. An optical performance report will be included to document the relevant physical and performance aspects of the samples provided. Deliver the prototypes to the Navy for evaluation.

PHASE III DUAL USE APPLICATIONS: Apply the knowledge gained in Phase II to build two lines of flight-demonstration units, suitably configured for a smallsat application, including flight spares, and characterize its performance in the UV/VUV as defined by Navy requirements. Working with the Navy and applicable Industry partners, demonstrate application to a Navy Space Test program (STP) flight test. Support the Navy for test and validation to certify and qualify the system for Navy use. Explore the potential to market and transition this capability to other military and commercial systems (NASA, University, Optics Industry). Commercial industries that may be able to use the developed technology include telecommunications and laser optics industries, and developers of systems designed for inspecting materials and medicines. Advances in EUV lithography for manufacturing integrated circuits may also provide a burgeoning opportunity for applying the developed technology. Market research and analysis shall identify the most promising technology areas and the awardee shall develop manufacturing plans to facilitate a smooth transition to the Navy.

REFERENCES:

1. Christensen, A.B.; Walterscheid, R. L.; Ross, M. N. et al. "Global Ultraviolet Imager (GUVI) for the NASA Thermosphere-Ionsphere-Mesosphere Energetics and Dynamics (TIMED) mission." Proc. SPIE 2266, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research, 1994. https://doi.org/10.1117/12.187583

2. Cotton, D. M.’ Stephan, A.; Cook, T.; Vickers, J.; Taylor, V. and Chakrabarti, S. "TESS: the tomographic EUV spectrographs." Applied Optics, 39(22), 2000, pp. 3991-3999. https://doi.org/10.1364/AO.39.003991

3. Dymond, K. F.;. Nicholas, A. C.; Budzien, S. A.; Coker, C.; Stephan, A. W. and Chua, D. H. "The Special Sensor Ultraviolet Limb Imager instruments." J. Geophys. Res. Space Physics, 122, 2017, pp. 2674-2685. https://doi.org/10.1002/2016JA022763

4. Sirk, M. M.; Korpela, E. J.; Ishikawa, Y. et al. "Design and Performance of the ICON EUV Spectrograph." Space Sci Rev., 212, 2017, pp. 631-643. https://doi.org/10.1007/s11214-017-0384-2

KEYWORDS: Spectroscopy; gratings; ultraviolet; vacuum ultraviolet; optics fabrication; remote sensing; optical imaging; spaceflight

TPOC 1: Bruce Fritz
Email: [email protected]

TPOC 2: Daniel Eleuterio
Email: [email protected]

TPOC 3: Andrew Stephan
Email: [email protected]

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