Low cost, high performance lightweight Aluminum mirror provides an alternative to glass ceramic, ceramic, and exotic metal mirrors. NASA funded several lightweight Aluminum mirror technology development efforts for future space and balloon-borne infrared telescope programs. As part of these efforts, subscale Al-SiC metal matrix composite, Aluminum-6061 and Aluminum-5083 mirrors, and additive manufactured AlSi10Mg mirrors were evaluated at room temperature to 20 degrees Kelvin for its optical performance. This paper will discuss objectives, material properties, fabrication, cryogenic testing infrastructure and instrumentation, thermal test results, modelling effort compared to empirical data, and lessons learned.
This paper describes POCO's new capability to rapidly produce large silicon carbide mirror substrates by conversion joining segments of silicon carbide during the process of converting graphite to silicon carbide. Mirror segments and structures are machined from a special graphite and subsequently joined together during the conversion process with the end result being a high purity beta silicon carbide structure. Interface boundaries are removed by the crystal growth across boundaries as the graphite crystal structure is converted to the larger crystal size of silicon carbide. Results of conversion joining development, design guidelines and limitations of the conversion joining process will be presented.
Silicon carbide may well be the best known material for the manufacture of high performance optical components. This material offers many advantages over glasses and metals that have historically been used in high performance optical systems. A combination of extremely high specific stiffness (E/r), high thermal conductivity and outstanding dimensional stability make silicon carbide superior overall to beryllium and low-expansion glass ceramics. A major impediment to wide use of silicon carbide in optical systems has been the cost associated with preliminary shaping and final finishing of silicon carbide. Because silicon carbide is an extremely hard and strong material, precision machining can only be done with expensive diamond tooling on very stiff high quality machine tools. Near-net-shape slip casting of silicon carbide can greatly reduce the cost of silicon carbide mirror substrates but this process still requires significant diamond grinding of the cast components. The process described here begins by machining the component from all special type of graphite. This graphite can rapidly be machined with conventional multi-axis CNC machine tools to achieve any level of complexity and lightweighting required. The graphite is then directly converted completely to silicon carbide with very small and very predictable dimensional change. After conversion to silicon carbide the optical surface is coated with very fine grain CVD silicon carbide which is easily polished to extreme smoothness. Details of the fabrication process are described and photos and performance specifications of an eight-inch elliptical demonstration mirror are provided.
Silicon carbide may well be the best known material for the manufacture of high performance optical components. A combination of extremely high specific stiffness (r/E), high thermal conductivity and outstanding dimensional stability make silicon carbide superior overall to beryllium and low- expansion glass ceramics. A major impediment to wide use of silicon carbide in optical systems has been the costs of preliminary pressing, casting, shaping and final finishing of silicon carbide. Diamond grinding of silicon carbide is a slow and expensive process even on machines specially designed for the task. The process described here begins by machining the component from a special type of graphite. This graphite is easily machined with multi-axis CNC machine tools to any level of complexity and lightweighting required. The graphite is then converted completely to silicon carbide with very small and very predictable dimensional change. After conversion to silicon carbide the optical surface is coated with very fine grain silicon carbide which is easily polished to extreme smoothness using conventional optical polishing techniques. The fabrication process and a 6 inch diameter development mirror is described.
We report the achievement of a superpolished surface, suitable for x-ray reflection, on bare stainless steel. The rms roughness obtained on various samples varied from 2.2 to 4.2 angstroms, as measured by an optical profiler with a bandwidth 0.29 - 100 mm-1. The type 17-4 PH precipitation-hardening stainless steel used to make the mirrors is also capable of ultrastability and has good manufacturability. This combination of properties makes it an excellent candidate material for mirror substrates. We describe the successful utilization of this type of steel in making elliptical-cylinder mirrors for a soft-x-ray microprobe system at the Advanced Light Source, and discuss possible reasons for its unusual stability and polishability.
Conference Committee Involvement (11)
Optomechanical Engineering 2019
14 August 2019 | San Diego, California, United States
Optomechanical Engineering 2017
9 August 2017 | San Diego, California, United States
Optomechanical Engineering 2015
11 August 2015 | San Diego, California, United States
Optomechanical Engineering 2013
27 August 2013 | San Diego, California, United States
Optomechanics 2011: Innovations and Solutions
23 August 2011 | San Diego, California, United States
Advances in Optomechanics
4 August 2009 | San Diego, California, United States
New Developments in Optomechanics
28 August 2007 | San Diego, California, United States
Optomechanics 2005
3 August 2005 | San Diego, California, United States
Optical Manufacturing and Testing VI
31 July 2005 | San Diego, California, United States
Optomechanics 2003
7 August 2003 | San Diego, California, United States
Optical Manufacturing and Testing V
3 August 2003 | San Diego, California, United States
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