telescope Secondary mirrors

Measuring space-based secondary mirror

 Optics bound for space need to be tested at the temperatures and pressures that they will experience in use. These measurements are made within large environmental chambers where cryogenic conditions can be simulated. Measurements of the mirror must be made with the interferometer either outside of the pressure chamber or with it isolated within its own chamber at atmospheric pressure. The chamber pumps create a high vibration environment which further disrupts measurements.

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.

 4D also offers high resolution PhaseCam and AccuFiz Fizeau Interferometers that can measure concave secondary mirrors with steep slopes or aspheric shape.

To verify control systems for adaptive optics, 4D’s PhaseCam systems can measure modal response to input signals and external vibration. Using feedback from the PhaseCam the response of an active optic’s actuators can be verified and calibrated. 

 NanoCam HD surface profilers are used to verify surface roughness on mirror surfaces. A NanoCam HD can measure directly on the mirror, or it can be mounted on a robotic positioner or gantry to measure anywhere on the mirror.  Because it can measure despite vibration, a  NanoCam HD can be mounted directly in a polishing station to guide the polishing process.

Added Technical Resources


Optical Metrology for Space and Terrestrial Telescope Optics

A paper that explores how Dynamic Interferometry measures in adverse conditions, providing in-situ feedback and that allows for faster, more confident production of large mirrors and space-based optics.


Measurement of Space Optics and Structures

An overview of the techniques and configurations used to build dynamic interferometers and measurement results for a variety of space-based optical components as well as the structures that hold them under simulated space-flight conditions. These techniques and configurations have applicability for many non-space applications as well.


Nano Surface Standards Gain Traction

Understanding the accuracy, resolution and stability of surface texture measurement results requires exacting nanoscale standards.

Products for Secondary Telescope 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.

AccuFiz D

Measures both sides of transparent, parallel optics as thin as 100 microns, surfaces in multi-surface optical systems, remote cavity test setups, and solid cavities such as etalons (laser rods).

Optical Profiling

NanoCam HD systems measure surface roughness on coated and uncoated surfaces to ensure the quality of polishing processes. 

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