Many large telescopes now employ adaptive optics on either their primary or secondary elements to counter the effects of constantly changing atmospheric conditions. One or more artificial stars are created using ground-based lasers. By imaging the artificial stars, a telescope’s adaptive system can adjust the active optic thousands of times per second to vastly improve image quality.
The actuators for the adaptive system are typically piezo elements attached to the back of flexible optical elements. Measuring how the adaptive optics respond to changes in their controlling actuators is critical to excellent performance. In the past, to measure the modal response of an adaptive optic to changes in the actuators, sensors have been used to measure movement at individual points on an optic— a slow, low-resolution solution.
4D PhaseCam Twyman-Green laser interferometers measure nearly instantaneously, so they can image adaptive optics as they are actuated. Data from the PhaseCam is used to verify and calibrate the response of the actuators. A PhaseCam can show the 3D response of the entire optic, providing a complete image of control system performance.
4Sight analysis software, included with all 4D interferometers, offers a modal analysis option which allows engineers to view the mirror response in real-time and to adjust the adaptive optic system accordingly.
4D’s PhaseCam Twyman-Green interferometers are able to measure despite vibration, even when situated many meters from the test optic. The PhaseCam has been the standard for long path and environment testing for nearly two decades.
Added Technical Resources
Phasing Telescope Mirror Segments
Summary of a paper about using a fast, two-wavelength interferometer to check alignment of multiple mirror telescope measurements.
Products for Adaptive Optics
Excels at fast, repeatable measurement of surface shape and transmitted wavefront error of flat and wedged optics. It is the most versatile Fizeau available, for any production environment.
Measures both sides of transparent, parallel optics as thin as 200 microns, surfaces in multi-surface optical systems, remote cavity test setups, and solid cavities such as etalons (laser rods).
NanoCam and FlexCam systems measure surface roughness on coated and uncoated surfaces to ensure the quality of polishing processes.