The demand for large (often > 1 meter diameter) optics has increased significantly, driven by growth in terrestrial and satellite-based astronomy, and defense and security applications. Laser interferometry is used throughout the manufacturing of large optics to ensure conformance to demanding design specifications. Measuring large optics is hampered by the presence of vibration, which is difficult to isolate in large test setups. Secondly, to measure the entire optical surface, the interferometer may need to be positioned far from the test piece—in some cases tens of meters away. Turbulence over such a large cavity can significantly distort the phase data, and airflow control systems of this scale are either expensive or impractical. Thirdly, modern telescope designs regularly rely upon non-traditional elements such as conformable mirrors, multi-segment mirrors or aspheric optics. Characterizint these elements creates yet more metrology challenges. 4D dynamic laser interferometers are used by the world's premier large optics manufacturers and telescope integrators to ensure excellent performance after installation. Their ability to measure despite vibration and to thrive in environments with significant turbulence makes 4D laser interferometers perfectly adapted to long stand-off measurements without vibration isolation. For space-based optics, 4D interferometers enable testing at cryogenic temperatures and/or low pressures, despite the extremely noisy environment around test vessels. Dynamic interferometry is often the only available option to complete these mission-critical measurements accurately and cost-effectively. Addressing the measurement of non-traditional optics, 4D systems make it possible to align mirror segments to sub-wavelength tolerances, to understand the modal response of adaptive optics, and to test aspheric optics using high-power lasers and computer-generated holograms (CGH). Virtually every major telescope and satellite-based optics program in recent years has relied upon 4D laser interferometers to ensure successful installation or deployment. For measuring large optics components and systems, 4D dynamic laser interferometers are in a class by themselves. |
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