There is a given when it comes to telescope lenses for use on earth or in space. The bigger the better! A bigger diameter implies greater optical resolution and light gathering power.
But making bigger and bigger mirrors and windows comes with some considerations for those wishing to deploy them, and for the companies charged with their fabrication.
First, bigger mirror and window size means significantly inflated cost, and this cost increase does not scale linearly. As the mirror size increases, costs increase exponentially. Second, in many instances applications demand that despite an increase in optic size, they need to be lightweight, and this may require that large scale optics be fabricated and mounted on an ultra-lightweight honeycomb structure, and this further increases cost.
With the expense and complicated fabrication and testing process to build large mirrors, supplier selection is critical to ensure project success. From the start your pool of suppliers is limited, as there are very few vendors that are able to make 0.5m sized mirrors and larger. ZYGO™ has this capability.
What other criteria do you need to assess to for the fabrication of a mirror that is fit for purpose and which is produced cost-effectively and in as timely a fashion as possible?
Material choice is a key factor in the optimization of optics in general and large optics in particular. When consulting with an optical manufacturer it’s important to know if customers are being steered in a direction because a particular vendor happens to synthesize a certain material, instead of recommending the material which is optimal for the prescribed application. ZYGO works with all leading material synthesizers on their latest developments to ensure we are ready to select the best material to meet the needs of the customer’s application. ZYGO collaborates with its customers and gives them the best advice for their specific application and works with the industry’s standard materials such as Sapphire (a-plane & c-plane), Multi-Spectral ZnS, ZnSe, Silicon Carbide, Fused Silica, Silicon, Zerodur, ClearCeram ULE, Germanium, CaF2, MgF2, Spinel, ALON, Cordierite, BK-7 and more.
When companies need to scale up the size of their windows and mirrors while maintaining the most exacting of optical specifications, the competence of a chosen partner is essential. With a large window there can be significant pressure from the airframe and it is critical that your chosen vendor understands how to determine flexural strength and edge strength to avoid catastrophic failure during the mission. A larger window can support a larger aperture imaging system, or multiple imaging systems plus LIDAR combined with other electromagnetic systems. Handling, mounting, and measuring all becomes more challenging as the size of the optic increases. Accounting for deformation and gravity sag can also prove to be challenging for an inexperienced team.
Also, your chosen vendor needs to validate that the mirror produced conforms to design intent. Manufacturers select a vendor that has the experience and confidence to meet leading-edge optical tolerances repeatably. Equally important is to work with a vendor that has the metrology expertise that can validate the quality of their work with reliable data. ZYGO’s manufacturing capability includes proprietary deterministic finishing that routinely achieves sub-nanometer global surface figure error, exceeding what most manufacturers are even capable of measuring.
And then there are post-fabrication issues. Selecting a vendor that specializes in manufacturing large optics is challenging; but if you need those optics coated, many vendors do not have chambers that can handle large optics. ZYGO is a fully-integrated optics provider, offering thin film coatings capability with chambers as large as 72”. The company’s coating capability ranges from the DUV 248nm-MWIR 5um. Capabilities include antireflective (AR) and highly reflective (HR) metallic coatings, conductive, beam splitter coatings, and high laser damage capability. Coating techniques include Magnetron sputtering, ion assisted E-beam, and fluoride deposition.
And finally, the heritage of your chosen vendor is important. When failure is not an option, integrators select partners with an established pedigree in optical component manufacture and assembly. ZYGO has a 40+ year space heritage working with such high-profile programs as Voyager, Skylab, ISS Cupola Windows, the Space Shuttle Hatch Window, and the Hubble Telescope Corrector Lens. Other world class programs include work with LIGO optics, Lawrence Livermore NIF, French Atomic Energy Commission (CEA), Rutherford Appleton Laboratory (RAL), and University of Rochester LLE. ZYGO’s electro-optical design, manufacture, and production segment has more optical assemblies in Low Earth Orbit (LEO) than any other company globally.