An aspheric surface is one in which various zones exhibit different curvatures, which at times can be radical. We can manufacture aspheres with varying departure specifications that range from a few waves to several hundred waves. Typical accuracies are one-tenth (1/10) wave peak-to-valley, although Exelis has manufactured better than one-thirty-fifth (1/35) wave peak-to-valley.
Typical large optical systems utilize an on-axis primary mirror as the key optic. Manufacturing these large aspheric optics is one of the core competencies for Precision Optics.
Systems such as Ikonos use on-axis aspheres for the primary mirror.
Quick and Inexpensive Complex Surface Designs
The generation of off-axis aspheric optics for remote sensing and astronomical ground based telescope systems used to be difficult, expensive and time consuming. Times have changed. Exelis can custom-manufacture these high precision optics. Today, Exelis can shape these complex surface designs inexpensively and quickly with a custom computer numerical control (CNC) off axis grinding machine.
Typical applications include tertiary mirrors for three mirror alignment telescopes and Z-fold optics required in smaller telescopes.
Applications and Capabilities
Among other applications, Exelis has used its precision-grinding capabilities to generate mirrors for large ground-based astronomical telescope assemblies, small off-axis optics for commercial remote sensing systems, and off-axis parabolic beam expander mirrors for the laser communications industry. These aspheric optics enable imaging systems to gather more light at higher resolution in small, lightweight packages.
- Custom Fabrication - Custom fabrication equipment from initial to finish stages of optical manufacture.
- State-Of-The-Art Optics - Manufacturing of state-of-the-art optics, which include 94% lightweight components with extreme departures.
- Range of Sizes - Sizes ranging from 6" diameter to 100" diameter (0.15 meter - 2.5 meter) f#'s greater than f1 have been achieved.
- Achieving a Ground Surface – Exelis high-precision aspheric generating machine can grind surfaces with slopes up to 20 degrees in raw blanks that range in size from 10 to 100in. (0.25 to 2.5m.) A bound abrasive grinding wheel generates optical surfaces with only 2 to 5 microns departure from the desired figure. Ground optics are then ready for polishing and figuring.
- Special Control Software - To cut within microns of a finished shape, a large off-axis machine requires accurate positioning of the cutter. Surface profile information measured with an onboard laser probe is fed to special control software developed by Exelis. The software calculates and plots the optic's surface error contours, and provides three-dimensional cutting tool paths for figure correction. Combined with the grinder's laser positioning feedback, and precision guideways and feedrates, software control gives engineers precise control of the cutting tool at all times.
- Time Savings - The highly deterministic nature of the off-axis generating machine enables Exelis to converge high-quality aspheric optics components in the 2m-size class with a minimum number of processing and test cycles. These and other complex optics once took many months to grind and figure. Now, they can be generated in weeks, with a corresponding cost savings.
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